The video provides a sobering reality check by shifting the focus from rocket engineering to the far more daunting task of re-engineering human biology. It masterfully illustrates that while we can build the ships, our own DNA remains the ultimate bottleneck for deep-space colonization.
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The Brutal Reality of Trying to Live on Mars
Added:You have 90 seconds to live on Mars. Not because of the cold, not because of the radiation, because the pressure is so low that the oxygen in your blood would literally start to bubble, your lungs collapse, and a better space suit doesn't fix it. [music] The obstacle was never really the technology. But what if we could change that? Here is a question. If you could change one thing about your own biology to survive on Mars, what would it be? Let me know in the comments. I will pin the most creative answer. Now, let's begin. 4 billion years of evolution crafted you as a masterpiece of adaptation to Earth.
Every system in your body is the product of countless generations of life, solving the specific problems of surviving here. Mars offers none of this. The Martian atmosphere is roughly 0.6% as dense as the one surrounding you right now. It is composed of about 95% carbon dioxide, a gas that is toxic to breathe in concentrated doses. The average surface temperature hovers around -60° C, though it can spike to a relatively balmy 20° near the equator during summer afternoons before plunging brutally at night. The gravitational pull on Mars is only about 38% of what you experience here. And without a global magnetic field, Mars lost its billions of years ago when its molten core cooled and solidified. And without a thick atmosphere to act as a buffer, the surface is constantly hammered by radiation. Solar ultraviolet light, solar energetic particles, and galactic cosmic rays all reach the surface with almost nothing standing in their way.
Every single one of those differences represents a direct sustained assault on a body that was never prepared to face them. But here is where the story gets genuinely breathtaking.
Life on Earth has not always looked the way it does today. Billions of years ago, the atmosphere of our own planet was radically different. There was almost no free oxygen. The dominant life forms were single-sellled microbes thriving in what we would consider a lethally hostile environment. No sunlight, no oxygen, crushing heat, choking volcanic gases. And then roughly 2.4 billion years ago, something extraordinary happened. An event scientists call the great oxidation event. Tiny organisms called cyanobacteria began releasing oxygen into the atmosphere as a byproduct of photosynthesis. And that changed the entire trajectory of life on Earth forever. Life did not surrender because the environment was hostile. It adapted.
It evolved. It found a way. So the question is never simply whether humans can survive on Mars in our current form.
We clearly cannot. The far more interesting question is what would need to change and could we actually engineer that change deliberately rather than waiting millions of years for natural selection to do it for us? The answer to that question lives at the crossroads of evolutionary biology, genetic engineering, neuroscience, psychology, [music] and some of the most remarkable scientific research happening on our planet right now. Humans have been staring at Mars for thousands of years.
The ancient Egyptians called it heresha, the red one. The Babylonians tracked its movements across the night sky with a precision that still impresses modern astronomers. The Romans named it after their god of war because of its blood [music] red color. For centuries, it sat there as a mystery, a wandering red star that moved in ways the fixed stars did not, captivating every civilization that looked up. Everything shifted in 169 when Galileo Galile pointed his rudimentary telescope toward Mars for the first time. He couldn't make out much surface detail, but he confirmed something fundamental. Mars was a sphere, a world, not merely a point of light. Over the following centuries, observers began assembling a picture of what Mars might actually be like.
Giovani Kaparelli mapped what he believed were canali channels on the Martian surface in 1877.
That Italian word was mistransated into English as canels implying they were artificially constructed and suddenly the entire world became captivated by the possibility of intelligent life on Mars. Perival Lel built a dedicated observatory in Flagstaff, Arizona, and spent years producing detailed maps of what he was convinced were an ancient civilization's irrigation [music] systems. Channels built to carry water from the polar ice caps to a dying, drying world. We now know those canals were an optical illusion, a trick of limited telescope resolution and eager human imagination. But the obsession they ignited that never died. The space age gave us our first honest look at the red planet. In 1965, NASA's Mariner 4 spacecraft completed a flyby of Mars and transmitted [music] 22 grainy black and white photographs back to Earth. The very first close-up images ever taken of another planet.
What they revealed was not the lush canalcovered world of romantic imagination.
They showed a barren, heavily [music] cratered surface that looked, to many people's disappointment, more like the moon than anything else. But science kept pressing forward. The Viking landers, arriving in 1976, became the first spacecraft to successfully operate on the Martian surface [music] for an extended period. They scooped up soil samples, ran biological experiments, and searched actively for signs of microbial life. The results were genuinely puzzling. Some experiments produced responses that looked on the surface like biological activity. Others produced no such signal. The debate over what Viking actually found continues among scientists to this very day. Then came a cascade of missions that transformed our understanding entirely. The Mars Pathfinder in 1997.
The twin Mars exploration rovers Spirit and Opportunity in 2004. Opportunity operating for an astonishing 14 years before a planetwide dust storm finally silenced it in 2018. The Curiosity rover, which landed in 2012 inside Gale Crater and is still operating as of today, sending back data about ancient lake environments and complex organic chemistry. And then Perseverance, which touched down in Jezero Crater in 2021 alongside the Ingenuity helicopter, the first powered aircraft ever to fly on another world. Each mission built on the last. We discovered that Mars once harbored liquid water, rivers, lakes, and possibly an ancient ocean covering a significant portion of its northern lowlands. We found complex organic molecules preserved in ancient sedimentary rock. [music] We detected methane in the atmosphere, a gas that on Earth is almost exclusively produced by living organisms, though geological processes can also generate it. And the source on Mars remains hotly debated. We mapped enormous deposits of water ice beneath the surface. And in 2018, data from the European Space Ay's Mars Express radar instrument suggested the possible existence of a subglacial lake of liquid water beneath the South Pole ice cap. A finding that subsequent research has since made more [music] complicated and uncertain, though not definitively ruled out. Mars is not a dead world. It is a layered, complex, ancient world full of unanswered questions, and it is waiting. But here is the thing that should stop you cold.
Every piece of data we've gathered, every rover track pressed into that rusty soil, every molecule analyzed, all of it points to one undeniable conclusion. Mars in its current state is not a place where a human being can simply step outside and exist. Not for 30 seconds, not without extraordinary protection. So the question of whether humans can live on Mars is not ultimately a question about Mars at all.
It is a question about us. Let's unpack that question one layer at a time.
Starting with something invisible, something that passes through walls and rock and flesh, something that could quietly dismantle your DNA one strand at a time. What is it? And is there actually a solution hidden inside the genomes of some of Earth's most extraordinary creatures? Let's talk about something you cannot see, cannot smell, cannot feel, and cannot hear.
something that is passing through your body right now at this very moment as you watch this video. It moves through the walls of your home, through the roof above your head, through your skin, your muscles, and the delicate [music] double helix of DNA coiled inside nearly every cell in your body. Most of the time, the damage is repaired so quickly and so efficiently that you never notice. Your body is extraordinary at fixing itself.
But now imagine removing every layer of protection between you and that invisible force. No magnetic field, no thick blanket of atmosphere, no ozone layer, just you standing on an open plane of red dust completely exposed.
That is what Mars does. Radiation on the Martian surface is not a distant theoretical concern. [music] It is an immediate, measurable, relentless reality. And it is one of the most serious biological threats that any human Mars mission will face. Not just during the journey there, but every single day on the surface. Here is some perspective that might genuinely unsettle you. NASA's Curiosity rover carries an instrument called the radiation assessment detector, RAD for short. It has been measuring radiation levels on the Martian surface [music] since 2012. What it found was sobering.
An astronaut spending 500 days on the Martian surface, roughly the minimum for a viable mission, would absorb a radiation dose of around 300 milliseverts just from galactic cosmic rays alone. Add the journey there and back, roughly 7 months each way through deep space where radiation exposure is even higher, and the total dose climbs to somewhere between 600 and 900 milliseverts. NASA's current career limit for astronauts is set between 600 and,200 milliseverts depending on age and gender. And those limits exist specifically because beyond them the risk of developing fatal cancer rises to levels that are considered unacceptable.
And that is during a quiet period of solar activity. A major solar particle event. A sudden eruption of high energy particles from the sun [music] can deliver a lethal dose in hours if you are caught without sufficient shielding.
Now, you might be thinking, can't we just build better shelters, bury the habitats under meters of Martian soil?
[music] And yes, those engineering solutions are absolutely being explored and they would help significantly. But they don't solve the problem of what happens when astronauts need to go outside or what happens during the journey itself or what happens to cells that are struck by galactic cosmic rays which are so penetrating that even the densest materials only partially slow them down. The engineering approach has limits and that's where biology becomes the most fascinating frontier. Because here is something remarkable.
Life on Earth has already solved the radiation problem. Not for Mars specifically, but some organisms have developed resistance to radiation doses that would kill a human being thousands of times over. And scientists are beginning to ask a genuinely radical question. [music] Can we borrow those biological solutions and apply them to us? Let's start with the most famous example. [music] You've almost certainly heard of the tardigrade, sometimes called the water bear. It's a microscopic animal barely half a millimeter long found in environments ranging from the deep ocean to the peaks of the Himalayas to patches of moss on city rooftops. Tardigrades are legendary in the scientific community for their almost supernatural resilience. They can survive in the vacuum of space. They can endure temperatures close to absolute zero and as high as 150° C. They can go without water for decades by entering a state called cryptobiosis, essentially pressing pores on all biological processes. And they can withstand radiation doses of up to 570,000 milliseverts. That is roughly 1,900 times the dose that would kill most humans. How? Scientists discovered a key part of the answer in 2016 when a team at the University of Tokyo identified a protein unique to tardigrades called DAP, short for damage suppressor. This protein physically wraps around DNA like a shield, preventing radiation induced breaks in the double helix. When researchers inserted the gene coding for DUP into human cells in a laboratory setting, those human cells showed approximately 40% less radiation induced DNA [music] damage than normal cells.
40% in human cells using a gene borrowed from a creature small enough to fit on the tip of a pin. That is not science fiction. That is a published peer-reviewed result. Then there is Dana Caucus radiourons, a bacterium that has earned the nickname Conan the bacterium in scientific circles and it absolutely deserves it. This organism can survive radiation doses of 1.5 million milliseverts. So far beyond anything a human could tolerate that the comparison almost loses meaning. It survives by having an extraordinarily efficient and redundant system for repairing DNA damage. When radiation shatters its genetic material into hundreds of fragments, Dinocus radiourine simply reassembles it with remarkable accuracy and remarkable speed. Researchers are actively studying its repair mechanisms in the hope of understanding which specific proteins and enzymes are responsible. with an eye toward one day incorporating similar pathways into human biology, either through genetic engineering or through pharmaceutical interventions that temporarily boost our own repair systems. And here is where it gets even more interesting. Within our own species, we see variation in radiation sensitivity. Some people carry genetic variants that make their DNA repair machinery more or less efficient.
There are individuals with mutations in genes like BRC1 and BRCA2 who are more susceptible to radiation induced cancer.
And conversely, there are genetic profiles that confer somewhat greater resistance. This tells us something profound. The human genome is not a fixed unchangeable blueprint. It is a collection of variations, possibilities, different configurations of the same fundamental code. And somewhere within that space of possibilities, there may be pathways we have not yet fully explored.
Now, this is the point where I want to be honest with you because this channel is built on that honesty. We are not at the stage where we can safely and ethically re-engineer human beings to be radiation resistant. The science of germline genetic modification making heritable changes to human DNA is one of the most ethically fraught territories in all of modern biology. The case of Hiangqui, the Chinese scientist who in 2018 announced he had created the world's first geneedited babies sent shock waves through the global scientific community and resulted in near universal condemnation.
We are not ready. The tools are improving rapidly, but the understanding of offtarget effects, unintended consequences, and long-term impacts is still far from complete. But the conversation is happening, and it will intensify as we get closer to actually sending people to Mars. Some researchers propose a middle path. not permanent genetic modification, but temporary biological interventions, drugs or biological agents that could temporarily upregulate DNA repair mechanisms during periods of high radiation exposure, compounds derived from the biochemistry of radiation resistant organisms, or even the use of crisper, the revolutionary gene editing tool that earned Jennifer Dudnner and Emmanuel Sharpantier a Nobel Prize in 2020 to make targeted reversible modifications that could be introduced for the duration of a mission. Others point to an entirely different approach. Rather than changing the human body, could we create a biological shield, a layer of engineered microorganisms living in or on the skin that absorb or neutralize radiation? Researchers at MIT have already been exploring the use of melanin producing fungi, including a species found thriving inside the heavily irradiated ruins of the Chernobyl nuclear reactor as potential radiation absorbing biological materials. A fungus called cladosporium sperosperm has been shown to use radiation as an energy source through a process called radioynthesis analogous to how plants use light in photosynthesis.
In 2020, a study even explored whether a thin layer of this fungus could provide measurable radiation shielding aboard the International Space Station. The results suggested it might [music] and it grew in space just fine. The universe, it turns out, has already spent billions of years engineering solutions to problems we are only now beginning to face. The challenge and the adventure is learning to read those solutions and apply them. But radiation is only the beginning. Even if we could solve the radiation problem entirely, the human body still faces a challenge so fundamental, so deeply embedded in our biology that many scientists consider it the single greatest physiological obstacle to long duration space flight. It's something you've never had to think about, something so constant and so invisible in your daily life that you take it completely for granted. By the way, if this kind of deep dive into the science of human survival in space is the kind of content you want to see more of, now is the perfect time to hit that subscribe button and leave a like. Every single one genuinely helps this channel grow and reach more curious minds like yours.
We're building something special here together, a community of people who aren't afraid to ask the big questions.
Now, we need to talk about gravity. Or more precisely, what happens to a human body when it doesn't have enough of it?
Because Mars has gravity, just not enough of it. At 38% of Earth's surface gravity, Mars sits in a strange in between zone that no human being has ever experienced for an extended period of time. We [music] have data from microgravity, the near weightlessness aboard the International Space Station.
We have data from the moon's gravity, which is about 17% of Earth's. But long duration exposure to exactly 38% gravity, we have no data. None. It is one of the great unknowns in human space medicine. What we do know from decades of research aboard the space station is that even short-term exposure to reduced gravity causes dramatic systemic changes throughout the body. and they begin faster than most people realize. Within the first few days of microgravity exposure, the body begins to redistribute fluids. [music] Without gravity constantly pulling blood and other fluids toward the lower body, they shift toward the head and chest.
Astronauts often describe feeling congested and puffyfaced in the early days of a mission. NASA calls this fluid shift, and it has real consequences for vision. The increased pressure of fluid around the brain can push against the back of the eye flattening and distorting the optic nerve and the eyeball itself. This condition called spaceflight associated neuroocular syndrome SANS has been documented in a significant proportion of long duration astronauts. Some have experienced permanent changes to their vision. Then there is the skeleton. Bones are living tissue constantly being broken down and rebuilt in a process called remodeling.
[music] On Earth, the mechanical stress of carrying your weight against gravity is one of the primary signals that tells your bones to remain dense and strong.
[music] Remove that signal and the remodeling balance shifts. In microgravity, astronauts lose bone mineral density at a rate of roughly 1 to 2% per month in weightbearing bones. [music] That's roughly equivalent to a decade's worth of osteoporosis related bone loss compressed into a single year. Muscle atrophy follows a similar pattern.
Without the constant work of moving against Earth's gravity, muscles begin to waste. Astronauts aboard the International Space Station exercise 2 hours every day precisely to slow this process. And they still return to Earth needing weeks [music] to months of rehabilitation before they can walk, run, and function normally again. The cardiovascular system changes, too. The heart, no longer needing to pump blood as hard against gravity, can actually decrease in mass and efficiency. The body in its [music] extraordinary efficiency adapts to the environment it finds itself in. The problem is that when that environment is not what the body was designed for, [music] adaptation can become dysfunction. Now 38% gravity on Mars is not zero gravity.
Mars is not the space station. The gravitational environment there would provide more stimulus to bones, muscles, and the cardiovascular system than true weightlessness [music] does. But is 38% enough to prevent the cascade of changes we see in microgravity? Honestly, and this is important to say clearly, we do not know and we won't know until someone actually spends significant time there.
What we do know is that we need to find out. And some researchers believe the answer might lie not just in exercise regimens or pharmaceutical interventions, but in something far more fundamental. The possibility of identifying and amplifying specific biological pathways that regulate bone and muscle maintenance, making the body more capable of preserving itself in lower gravity environments. Studies of animals that hibernate, bears for instance, have revealed fascinating mechanisms. During months of immobility and reduced metabolic activity, hibernating bears lose far less bone and muscle mass than you would predict based on what we see in bedridden humans.
Something in their biology actively protects those tissues. Research has identified specific hormones and signaling molecules involved in this process and some scientists believe that understanding and potentially replicating those mechanisms could be a key tool for longduration space flight.
The human body is not a static machine.
It is a dynamic, responsive, adaptive system. The question of Mars is not whether that system can change. It clearly can and does. The question is whether we can learn to direct that change consciously, deliberately, and safely. And that question doesn't stop at the body. Because after months in a sealed habitat, after the isolation, the confinement, the distance from every person you have ever loved, after staring at the same four walls, while a radiation laced dust storm howls outside for weeks on end, the mind begins to change, too. The psychological dimension of a Mars mission is something that scientists are only beginning to fully grapple with. And what they're finding raises questions that go far deeper than just will astronauts get depressed. The answers touch something fundamental about what it means to be human, about what our brains were actually built for, and about whether consciousness itself can make the leap to another world. What does a human mind do when it is truly, utterly, irreversibly far from home? And is there a version of us that could handle it? Not just survive it, but actually flourish in it. That is exactly where we're going. Don't go anywhere.
There is a moment that every astronaut on the International Space Station eventually experiences. It happens quietly, usually when they drift toward one of the cup windows. that beautiful multi-paneed observatory module that juts out from the station like a glass bubble pointed at the earth below. They look down and there it is. Home. The whole thing all at once. The blue of the oceans, the white swirl of clouds, the thin luminous line of the atmosphere, that impossibly delicate membrane between life and the void. And in that moment, something shifts inside them.
Scientists have a name for it. The overview effect. It was first described by author Frank White in 1987 after interviewing astronauts about their experiences in orbit. Over and over again, they described the same thing. A sudden overwhelming shift in perspective. A feeling of profound interconnectedness.
A realization visceral and immediate and almost impossible to put into words that the boundaries we draw between nations, between peoples, between ourselves and the natural world. All of them are invisible from up there. All of them are human inventions painted onto a living sphere floating in an ocean of darkness.
Edgar Mitchell, the sixth person to walk on the moon during Apollo 14 in 1971, described looking out at the universe during his return journey and experiencing what he called a sudden sense of universal connectedness, an instant global consciousness. He said it was the most profound experience of his life. He spent the rest of his years trying to understand it scientifically.
The overview effect is real. It has been documented consistently across astronauts of different nationalities, different backgrounds, different personalities.
Neuroscientists and psychologists believe it may involve a fundamental reorganization of the brain's default mode network, the system responsible for self-referential thought, our sense of identity, and our relationship to the world around us. When the visual and cognitive input of seeing the entire Earth as a single fragile object overloads the usual frameworks the brain uses to understand its place in the world, something new emerges. Now, here is the question that keeps space psychologists up at night. What happens on the way to Mars when Earth is no longer a stunning blue sphere filling your window, but just another point of light smaller than a thumbnail?
indistinguishable eventually from a moderately bright star. What happens to the human mind then? This is not a hypothetical concern. At its closest approach, Mars is about 54.6 million km from Earth. At its farthest, it is over 400 million km away. The speed of light, the absolute cosmic speed limit, means that a radio signal sent from Mars takes anywhere from 3 minutes to over 22 minutes to reach Earth, depending on where the two planets are in their orbits. A conversation with anyone back home becomes impossible. A message sent, a wait, a reply, disconnected, asynchronous, achingly slow. In a genuine emergency, you cannot call for help and receive a useful response in time to act on it. You are in every practical and psychological sense on your own. And the human brain was not designed for that. We are at the most fundamental neurological level a deeply social species. Our brains did not evolve in isolation. They evolved in groups, small, tight-knit communities where reading the emotions of others, maintaining social bonds, and navigating the complex web of interpersonal relationships where survival skills as important as finding food or avoiding predators. The regions of our brain devoted to social processing are enormous compared to most other animals.
We are wired for connection. We need it the way we need oxygen and food and sleep. Studies of people kept in prolonged isolation, whether voluntarily as in certain meditation retreats or involuntarily as in solitary confinement, consistently show that the human brain begins to change in measurable ways. Anxiety rises, cognitive function declines, emotional regulation becomes harder. In extreme cases, hallucinations begin. The brain starved of the social input it craves starts generating it internally and not always in healthy ways. Now multiply that by a crew of six people sealed inside a habitat roughly the size of a small apartment for months or years with no ability to truly escape each other or get genuine privacy while simultaneously dealing with the knowledge that the nearest human backup is [music] 22 light minutes away at the speed of light. This is the psychological landscape of a Mars mission and it [music] has been studied not on Mars obviously but in the closest analoges we can create here on Earth.
One of the most important of these is the HICS program. Hawaii space exploration analog and simulation.
Beginning in 2013, NASA funded a series of long duration isolation studies [music] in a geodessic dome habitat perched on the Baron. Lava covered slopes of Mana Lower on the Big Island of Hawaii. The location was chosen deliberately. Its stark reddish rocky landscape is one of the most Mars-like environments found anywhere on Earth.
Crews of six people lived inside the dome for periods ranging from 4 months to one full year, following simulated Mars mission protocols. They wore simulated space suits when going outside. They experienced communication delays with the outside world. They managed their own conflicts, their own morale, their own psychological health with minimal outside support. What they found was illuminating and sobering in equal measure. Interpersonal conflict was the single most consistently identified challenge across missions.
Not technical problems, [music] not physical discomfort. People specifically the friction that builds between human beings when they are perpetually in each other's space. When escape is impossible. When small irritations compound over weeks and months into serious tension. [music] Researchers identified what they called thirdarter phenomenon, a marked dip in crew morale, cohesion, and performance that reliably occurred about 3/4 of the way through a mission. It appeared in multiple crews across different mission lengths with different people. It seems to be something like a universal human response to prolonged confinement. A psychological wall that gets hit when the initial excitement has worn off and the finish line still feels far away.
[music] Leadership dynamics also emerged as critical. Crews with clearly defined, respected leadership and wellestablished roles tended to navigate conflict more effectively. Crews where authority was ambiguous or contested struggled significantly more. The social architecture of a crew, who has what role, how decisions get made, how disagreements are resolved, turns out to matter as much as the technical competence of its members. Then there is the research coming out of Antarctic winter overstations which have been providing data on human psychology in isolated, confined and extreme environments for decades. The Concordia research station jointly operated by France and Italy on the Antarctic Plateau is particularly valuable.
[music] It sits at an altitude of over 3,200 m, experiences temperatures as low as -80° C, and is completely cut off from the outside world for 9 months of the year during the polar winter. The researchers stationed there cannot leave, cannot receive visitors, and face months of total darkness during the polar night. Studies of Concordia crew members have documented changes in cognitive performance, mood, immune function, and even the microbiome, the community of microorganisms living in and on the human body. Sleep patterns shift. Circadian rhythms are disrupted by the absence of normal light cycles.
One particularly striking finding involves what researchers describe as a kind of psychological hibernation, a flattening of emotional response, a narrowing of attention to immediate tasks, a withdrawal from complex social and intellectual engagement that appears to be an adaptive response to the relentless sameness of the environment.
The brain in some sense powers down non-essential functions to conserve itself. This phenomenon has a clinical name. It is sometimes called the winter over syndrome or in the Antarctic research community simply the Antarctic stare. A kind of subtle cognitive and emotional withdrawal that longtimers recognize in each other. It is not mental illness in the traditional sense.
It is adaptation. But it raises a profound question. If the brain adapts to Mars in similar ways, does that adaptation help or hinder the incredibly complex scientific and engineering work that a Mars crew would need to perform?
And underneath all of this runs a thread that is perhaps the most philosophically challenging aspect of the whole endeavor. The concept of home. Every human being who has ever lived has grown up under the same sky. has breathed the same air in the sense that every breath you take contains molecules that have cycled through the bodies of billions of living things before you through Julius Caesar and ancient sea creatures and the first flowering plants has looked up at the same moon, the same stars, the same sun. We carry earth in our biology, yes, but we also carry it in our psychology, our culture, our language, our myths, our religions, our art. Every human story ever told has been set on this one world. A person born on Mars, if such a thing ever happens, would grow up under a butterscotch sky, would know two moons, would know a gravity weaker than their parents grew up with. Would look up at night and see Earth as a bright blue star the way we see Mars.
Beautiful, distant, another world. They would be in every meaningful sense, not quite the same kind of human as the people who sent their ancestors there.
That thought is not unsettling. It is extraordinary because it means that the story of humanity, if we make it to Mars, does not end. It branches like a river reaching a delta, splitting into new channels. Each one flowing toward a different ocean. But before that branching can happen, before a child can be born under a Martian sky, the adults who go there first need to survive. And survival on Mars means confronting one more biological challenge that most people never even think about. Something that happens at the microscopic scale inside every one of the roughly 37 trillion cells in your body. It has to do with time and energy and a structure so fundamental to life that its malfunction is linked not just to the difficulties of space travel, but to aging itself. I'm talking about the mitochondria and I'm talking about what cosmic radiation does to them over months and years of deep space exposure.
But there is something else too.
Something that emerges from the intersection of radiation damage, cellular stress and the strange new gravitational environment of Mars.
Something that researchers have only recently begun to identify and name. And when you understand it, it will change how you think about what the human body is actually capable of and what it might need to become. That is coming up next.
But I want to leave you with a thought to sit with until then. Every single technological and biological challenge we face on the road to Mars is at its root a question about what we are willing to become. Every solution requires us to look honestly at the limits of our current form and ask whether those limits are fixed or whether they are simply the starting point. 4 billion years of life on Earth produced a creature capable of looking up at the stars and wondering what lives there. That same process of wonder, of curiosity, of reaching beyond what is comfortable and known. That is what got us this far. and it is what will carry us further. The universe has been running experiments in biology for longer than the sun has existed. We are one of its results. Mars might one day produce another. Let's go small, impossibly small, smaller than anything you can see with the naked eye. Smaller than anything visible under a basic microscope. We are going to shrink down past the level of tissues and organs, past individual cells, past the membrane and the nucleus, all the way down to the molecular machinery that keeps you alive. The engines humming inside every cell of your body, converting food and oxygen into the energy that powers every thought you think, every heartbeat, every breath. We are going to talk about mitochondria. You've probably heard the phrase, "The mitochondria is the powerhouse of the cell." It has become something of an internet joke at this point. A meme born from the repetition of middle school biology lessons. But strip away the humor for a moment because what mitochondria actually are and what happens to them in the environment of deep space is one of the most important and least discussed stories in human spaceflight science.
Mitochondria are not simple structures.
They are in the most literal evolutionary sense not originally human at all. Roughly 1.5 billion years ago, a momentous event occurred in the history of life on Earth. A primitive cell engulfed a bacterium and instead of digesting it, something unprecedented happened. The two organisms formed a permanent partnership. The bacterium took up residence inside the host cell, providing energy in exchange for protection and resources. Over billions of years of co-evolution, that ancient bacterium became what we now call the mitochondrian. It still carries its own separate DNA, a circular genome completely distinct from the DNA in your cell's nucleus, a living relic of that ancient merger. Every mitochondrian in your body is in a deep evolutionary sense a descendant of a free-living bacterium that struck a deal with an early ancestor of yours over a billion years ago. That partnership is the foundation of all complex life on Earth.
And it is exquisitely specifically tuned to the conditions of this planet. Now here is where space comes in. Research conducted aboard the International Space Station and analyzed in rigorous detail back on Earth has shown that spaceflight causes significant disruption to mitochondrial function. The combination of radiation exposure, microgravity, disrupted sleep cycles, elevated carbon dioxide levels, and chronic physiological stress creates a cascade of effects that hit the mitochondria hard. Oxidative stress, the accumulation of chemically reactive molecules called reactive oxygen species, which are normal byproducts of mitochondrial energy production, but become damaging in excess, increases substantially in spaceflight conditions. Mitochondrial membranes, which are critical to their function, are particularly vulnerable to radiation induced damage. The efficiency of energy production drops. cells begin to function less effectively and the downstream effects ripple through the body in ways that researchers are still mapping. But the most dramatic, the most scientifically stunning window into what space actually does to human biology at the cellular level came from one extraordinary natural experiment. An experiment that could only happen because of one remarkable fact. NASA had a pair of identical twin astronauts, Scott and Mark Kelly, born 11 minutes apart in Orange, New Jersey, in 1964.
Both naval aviators, both selected as NASA astronauts in the same class. In 1996, genetically as close to identical as two human beings can be. And in 2015, Scott Kelly launched to the International Space Station for what would become a 340day mission, the longest single space flight by an American astronaut at the time.
His brother Mark stayed on Earth. For the first time in history, NASA had a living control experiment, the same genome expressed in two different environments, one in space, one on Earth, for nearly a full year. The results published in the journal Science in 2019 by a team of dozens of researchers across multiple institutions were genuinely revoly and in some cases genuinely alarming. Scots telomeres lengthened during space flight. Now, if you're not familiar with telomeres, here is a quick picture. Imagine your DNA as a shoelace. The telomeres are the little plastic caps on the ends. They protect the genetic information from fraying and degrading every time the cell divides.
As we age, those caps get progressively shorter with each cell division. When they get short enough, the cell can no longer divide safely and either stops functioning or self-destructs. Telmir shortening is one of the fundamental mechanisms of biological aging. Scott's telomeres got longer in space, which sounds like great news, right? Except that when he returned to Earth, they rapidly shortened again and in some cases contracted shorter than they had been before the mission. The dramatic fluctuation itself appears to be a sign of cellular stress, not cellular health.
the body swinging wildly between states, struggling to maintain equilibrium in an environment it was never built for. But that wasn't the most striking finding.
The study also found changes in gene expression, which genes were switched on or off across thousands of genes in Scott's cells. Changes in cognitive performance detectable through testing and brain imaging. Changes in his microbiome, the ecosystem of microorganisms living in his gut, which plays a critical role in immune function, metabolism, and even mood.
Changes in DNA methylation patterns, chemical tags on the genome that regulate how genes are read that are associated with aging and cancer risk.
And here is the detail that stopped the scientific community cold. About 7% of the changes in Scott's gene expression did not return to baseline after he came home. Even after months back on Earth, those genes remained in their altered state. The researchers were careful to note that this does not mean Scott's DNA sequence changed. His actual genetic code remained the same. But the way that code was being read, the pattern of which genes were active and which were silent had been permanently shifted by his time in space. 7% sounds small. But consider this. The difference in gene expression between a healthy cell and a cancerous one can involve far fewer genes than that. The difference between a young cell and an old one in terms of gene expression patterns is measured in percentages like these. That 7% represents a meaningful, measurable, lasting biological imprint left by 11 months in space. Now, the twin study was conducted in low Earth orbit, far closer to home than Mars would be, and still within the partial protection of Earth's magnetic field. A Mars mission would expose astronauts to dramatically higher cumulative radiations doses, longer durations, and the additional physiological insult of the Martian surface environment. If 11 months in the relatively sheltered environment of the space station produces changes this profound, what would 3 years in deep space do? This is the question driving some of the most urgent research in space medicine right now and [music] scientists are pursuing answers from some genuinely unexpected directions.
One of the most promising involves a molecule called NAD+ nicotinomide adinine ducleotide. It's a co-enzyme found in every living cell. Absolutely central to mitochondrial energy production and to the function of a family of proteins called sertuins which play a crucial role in DNA repair, inflammation regulation and the cellular stress response. NAD plus levels decline naturally with age and they decline in spaceflight conditions as well.
Researchers at Harvard Medical School, led by David Sinclair, have been investigating whether boosting NAD+ levels could protect against both the cellular damage of aging and the cellular damage of radiation exposure.
Studies in mice showed that animals given NAD plus precursors before radiation exposure experienced significantly less DNA damage than controls. Human clinical trials exploring the effects of NAD plus precursors on aging and cellular health are underway, though results specifically for spaceflight protection are still in early stages. Another avenue involves senolytics, a class of drugs designed to selectively clear out what biologists call scinescent cells.
Seniccent cells are cells that have stopped dividing, [music] often because their telomeres have gotten too short or because they have sustained too much DNA damage. But instead of dying, they linger in tissues and release a cocktail of inflammatory molecules that damage surrounding healthy cells. They are sometimes called zombie cells. No longer fully functional, but too stubborn to go away and actively causing harm by staying, scinsesscent cells accumulate in tissues exposed to radiation, and researchers believe they may be a key driver of the long-term health consequences of space flight. Drugs that can safely identify and eliminate these zombie cells while leaving healthy cells untouched are one of the most actively pursued areas in both aging research and space medicine. There is also extraordinary work happening in the field of epigenetic reprogramming. The idea championed by researchers like Shina Yamanaka who won a Nobel Prize in 2012 for his discovery of induced purip potent stem cells that the epigenetic age of a cell how old it behaves can potentially be reset. The Yamanaka factors a set of four proteins can take a specialized adult cell and reprogram it back toward a stem cell-like state.
More recently, researchers, including those in David Sinclair's laboratory, have explored whether partial controlled application of epigenetic reprogramming factors could reverse aging associated changes in cells without turning them back into uncontrolled stem cells. A careful targeted reset rather than a full rewind. Results in animal models have been striking. translation to human medicine is still years away. But the concept that the biological clock is not a one-way ratchet that cells carry within them the information needed to restore a younger state is one of the most profound ideas in modern biology.
Blauio that to space medicine and the implications are extraordinary. If we could develop safe, effective methods of periodically resetting the epigenetic age of cells in astronauts during a long duration mission, counteracting the accelerated aging effects of radiation and physiological stress, the timeline of what is biologically survivable in space expands dramatically. And then there is the microbiome. This is a dimension of human biology that has exploded in scientific significance over the past two decades. The community of microorganisms living in and on your body estimated to contain tens of trillions of individual organisms representing thousands of species is not a passive passenger. It is an active dynamic organ system. It influences immune function, digestion, metabolism, hormone levels, neurotransmitter production, and increasingly evidence suggests mood and cognitive function through what researchers call the gut brain axis. In space, the microbiome changes substantially. The composition of microbial communities shifts. Some beneficial species decline. Some potentially harmful ones proliferate.
The immune system's relationship with the microbiome becomes disregulated. And given how central the microbiome is to overall health, these changes have cascading effects throughout the body, researchers are exploring whether carefully designed probiotic and prebiotic interventions, essentially actively managing the microbial communities in astronauts guts could help maintain immune function, metabolic health, and even psychological well-being during long duration missions. Some are going further, asking whether synthetic biology could be used to engineer microorganisms specifically designed to thrive in the gut under spaceflight conditions and provide benefits that the native microbiome can no longer supply. We are in a very real sense not just one organism. We are a community. And taking that community to Mars means thinking about what happens to all of it. Not just the human cells, but the invisible ecosystem they depend on. Every thread we pull on in this story leads us deeper into the same fundamental realization. The human body is a system of extraordinary complexity and extraordinary adaptability. But it is a system built for one specific context. Changing that context by putting it on another world does not break the system. It reveals the edges of it. And at those edges, we find the most fascinating questions in all of science. What can be changed? What must be changed? And what, if anything, do we risk losing in the process of becoming something new? Because adaptation always has a cost. Evolution never gives you something for nothing. Every trait gained is somewhere a tradeoff. The organisms that are most radiation resistant are not by and large the organisms building radio telescopes and writing poetry and launching spacecraft.
Simplicity confers resilience.
Complexity confers capability. The challenge of making humans fit for Mars is at its core the challenge of preserving the complexity, the consciousness, the creativity, the emotional depth, the social intelligence while building in the resilience that complexity currently lacks. That is not just a biological problem. It is a philosophical one. It is in the deepest sense a question about what we value most about being human. And it connects directly to the next dimension we need to explore. Because even if we solve the radiation problem, even if we protect the mitochondria, even if we preserve the microbiome and arrest the cellular aging, there is still something that no amount of biochemical engineering fully addresses.
The thing that makes you you. The seat of your experience, your memories, your relationships, your sense of meaning and purpose. The organ that will need to navigate a world of perpetual rust and thin air and distant stars. And the overwhelming knowledge that every person you have ever loved is a pale blue dot in the night sky. your brain and specifically what happens to it. Not just psychologically, as we explored in part three, but neurologically at the level of neurons and synapses and the bloodb brain barrier and the structural changes that space flight imposes on the most complex object in the known universe. Because what the research is revealing about what space does to the brain, the actual physical structure of it is something that deserves its own conversation entirely. Now we go inside the brain itself. The bloodb brain barrier, white matter changes, cerebrros spinal fluid shifts, and the emerging provocative idea that the brain might need to be fundamentally different, not just tougher, but differently organized to truly thrive across the void between worlds. That conversation starts right after this. Don't go anywhere. This next part might be the most surprising of all. There is an organ sitting inside your skull right now that contains roughly 86 billion neurons. Each one of those neurons can form thousands of connections with other neurons, synapses, tiny electrochemical bridges across which information flows in patterns of almost incomprehensible complexity. [music] The total number of synaptic connections in a single human brain is estimated to be around 100 trillion. That number exceeds the total count of stars in the Milky Way galaxy by a factor of roughly 1,000. The human brain is by any measure we currently possess the most complex structure in the known universe. And space flight is changing it physically, structurally, in ways that show up clearly on brain scans, in ways that persist after astronauts return home, and in ways that scientists are only now beginning to fully understand. This is not a metaphor. This is not about stress or anxiety or the psychological challenges we talked about in part three, though those are real and serious. This is about the literal measurable physical architecture of the brain shifting in response to the space environment.
Ventricles enlarging, white matter changing, the brain actually moving upward within the skull, and the system designed to protect it. One of the most elegantly engineered biological structures in the human body being disrupted in ways that may have consequences we are only beginning to appreciate. Let's start with something called cerebrros spinal fluid. You probably haven't thought much about it, but it is absolutely essential to your survival. It's a clear colorless liquid that surrounds and cushions your brain and spinal cord, providing mechanical protection, removing metabolic waste products, and helping regulate the chemical environment of the central nervous system. Your brain produces it continuously and absorbs it continuously, maintaining a careful equilibrium of pressure and volume. In space, that equilibrium is disrupted.
When the body's fluids shift toward the head in microgravity, that same fluid redistribution we talked about earlier, cerebrros spinal fluid dynamics change as well. The fluid that normally drains downward due to gravity no longer does so as efficiently. Pressure builds in and around the brain. The brain itself, studies have shown, physically shifts upward within the skull toward the top of the head as the supporting fluid redistributes. The ventricles, fluid fil cavities deep within the brain, enlarge.
Research published in the New England Journal of Medicine in 2017 analyzed MRI brain scans of astronauts before and after longduration space flights. The findings were striking. The majority of astronauts showed measurable narrowing of the central sulcus, a key groove running across the top of the brain that separates the motor cortex from the sensory cortex. The brain tissue itself had shifted upward far enough to compress this groove. And crucially, this change did not fully reverse after the astronauts returned to Earth. Years later, follow-up scans showed that the structural alterations persisted in many cases. Let that sink in for a moment. A relatively short stay in space compared to what a Mars mission would require produced lasting structural changes in the physical architecture of the brain.
But the disruption goes deeper still.
The bloodb brain barrier is one of the most remarkable structures in human biology. It is a highly selective membrane formed by specialized cells lining the blood vessels of the brain.
Designed to control precisely what substances can pass from the bloodstream into the delicate neural environment. It keeps out pathogens, toxins, and many drugs while allowing oxygen, glucose, and essential nutrients through. It is the brain's bouncer. Extraordinarily discerning, extraordinarily important.
Research conducted both in animal models and increasingly in human astronauts suggests that spaceflight compromises the integrity of the bloodb brain barrier. The combination of radiation exposure, fluid shifts, elevated intraraanial pressure and physiological stress appears to make this barrier more permeable, allowing substances through that would normally be kept out.
inflammatory molecules, potentially harmful compounds, things the brain's internal environment is not equipped to handle. The neurological consequences of a chronically compromised bloodb brain barrier [music] can include increased neuroinflammation, a state of persistent low-level immune activation within the brain that is associated in terrestrial medicine with a growing list of neurodeenerative conditions including Alzheimer's disease, Parkinson's disease, and others. It is associated with cognitive decline, mood disruption, and impaired sensory processing. Now add to this the direct effects of cosmic radiation on neural tissue. Galactic cosmic rays are not just a threat to DNA in dividing cells. They are a threat to neurons specifically. And here is what makes this particularly concerning. Neurons, unlike most cells in the body, do not regenerate easily. You are born with the vast majority of the neurons you will ever have. Damage to them tends to be permanent in a way that damage to say liver cells or skin cells is not.
studies in rodents exposed to simulated galactic cosmic ray radiation conducted at facilities like the NASA Space Radiation Laboratory at Brook Haven National Laboratory in New York have shown measurable cognitive impairment including deficits in spatial navigation, learning and memory. Changes in the structure and density of dendritic spines, the tiny protrusions on neurons where synaptic connections form, increased neuroinflammation and behavioral changes consistent with what we would in a human context describe as anxiety and reduced cognitive flexibility. Charles Limoli, a neuroscientist at the University of California, Irvine, who has spent years studying the effects of space radiation on the brain, has published findings showing that even relatively low doses of the kinds of radiation encountered in deep space significant and lasting changes in the neural circuitry of rodents. His work has been sobering for the space medicine community, not because it proves humans will suffer irreversible brain damage on the way to Mars, but because it demonstrates clearly that the brain is not immune to the space environment in the way we might hope, and that the consequences may extend well beyond what traditional radiation risk models predicted. There is also something happening at the level of white matter. the vast network of insulated neural pathways that connect different regions of the brain to each other, allowing information to travel efficiently across the whole system.
Think of gray matter as the processing centers, the cities, and white matter as the highways connecting them. Research using advanced MRI techniques, including diffusion tensor imaging has documented changes in white matter integrity in astronauts after long duration space flight. The highways show signs of wear.
Connections that should be crisp and efficient appear subtly altered.
Cognitive testing of astronauts returning from long missions has documented realworld consequences.
slowed processing speed, reduced spatial orientation ability, the capacity to understand and navigate three-dimensional space, which is incidentally rather important when you are piloting a spacecraft or navigating the surface of another planet. Working memory changes, shifts in fine motor control. Most of these effects improve after astronauts return to Earth and readapt to a normal gravitational and radiation environment, but most and improve are not the same as all and fully reverse. And a Mars crew cannot return to Earth after a rough month to recover. They are committed in a way that no human being has ever been committed to anything to seeing it through. So what do we do about it?
Scientists are pursuing several lines of research simultaneously and some of them are genuinely fascinating. One involves neuroprotective compounds, substances that shield neurons from damage or support their repair. Lithium long used as a mood stabilizer in psychiatry has shown neuroprotective properties in a range of studies and has been proposed as a potential intervention for radiation induced neurological damage.
Antioxidant compounds that specifically cross the bloodb brain barrier and neutralize the reactive oxygen species generated by radiation are being investigated. So are [music] drugs that target neuroinflammation specifically reducing the brain's chronic inflammatory response without broadly suppressing the immune system. Another approach involves cognitive training and neuroplasticity.
The brain's ability to reorganize itself to form new connections, reroute information around damaged areas, adapt its structure and function in response to experience [music] is one of its most extraordinary properties. Intensive cognitive training regimens specifically designed to maintain and enhance the neural circuits most vulnerable [music] to space related degradation may help preserve function even as the physical environment exerts its pressure. Virtual reality environments that challenge spatial navigation, working memory, and executive function are being developed and tested for long duration mission crews. There is also the remarkable emerging field of neuro stimulation.
Non-invasive techniques like transcranial direct current stimulation and transcranial magnetic stimulation can modulate neural activity in targeted brain regions [music] without surgery or drugs. Researchers are exploring whether these tools could be used to maintain cognitive performance and counteract the neural effects of space flight during long missions. The technology is advancing rapidly driven in part by its applications in treating depression, stroke rehabilitation, and cognitive decline here on Earth. But there is a more radical idea beginning to percolate at the edges of the scientific conversation. And it asks not just how we protect the brain we have, but whether the brain itself might [music] need to change. Consider the following.
The human vestibular system, the inner ear apparatus that tells you which way is up, how fast you are moving, [music] whether you are accelerating is exquisitely calibrated for Earth's gravitational field. It is so finely tuned to 1G that even brief exposure to different gravitational environments causes profound disorientation.
Space sickness, the nausea and disorientation that afflicts the majority of astronauts in the first days of a mission is essentially the vestibular system receiving input that contradicts everything it has ever known. It is not weakness. It is the price of precision. On Mars at 38% [music] gravity, the vestibular system would need to recalibrate completely.
How long does that take? How complete is the adaptation? And are there individuals whose vestibular systems are constitutionally more adaptable, more plastic than others? If so, could those individuals be identified before a mission? Could plasticity be enhanced pharmacologically or through training?
And going further, if we think about a population of humans living on Mars across multiple generations, natural selection would over deep time favor individuals whose nervous systems adapt more easily to Martian gravity, whose brains are more resistant to the specific kinds of radiation encountered on the Martian surface, whose bloodb brain barriers are more robust under conditions of elevated intraranial pressure. Evolution has always been the slowest, most patient engineer. But what if we do not have millions of years to [music] wait? This is where the conversation about directed human evolution, about intentional genetic and biological modification of the human brain and nervous system becomes impossible to avoid. It is controversial. It is ethically complex in ways that require serious, careful societywide deliberation. But it is also increasingly scientifically plausible in ways it simply was not a decade ago. The crisper revolution has given us tools to edit the genome with a precision and accessibility that would have seemed like fantasy to the scientists who discovered the double helix structure of DNA in 1953.
The emerging science of epigenetic engineering, modifying not the DNA sequence itself, but the chemical tags that determine how it is read, offers additional levers. and the rapidly advancing field of brain computer interfaces driven by projects like Elon Musk's Neurolink and academic research programs around the world raises the possibility of augmenting neural function not through biology alone but through the integration of biological and electronic systems. A brain augmented with the ability to more efficiently process and adapt to sensory environments different from Earth. A nervous system supported by implanted systems that monitor and counteract the early signs of radiation induced neuroinflammation.
A human being who is in ways both biological and technological more than what evolution alone produced. This is not science fiction. It is the direction of travel of the science and the distance between current capability and these possibilities is shortening faster than most people realize. But I want to bring this back to something human, something felt rather than measured.
Because at the end of all these numbers, all these mechanisms, all these extraordinary biological details, there is a person. There is a human being lying in a bunk in a small metal habitat on the surface of another world, staring at the ceiling, listening to the wind outside, a Martian wind that cannot be felt through a suit that moves dust but carries no sound through an atmosphere thin enough to be nearly vacuum. And thinking about home, thinking about people they love, thinking about whether this was worth it. What that person's brain needs is not just protection from radiation and fluid dynamics. [music] It needs meaning. It needs connection. It needs the sense that what they are doing matters not just scientifically, not just historically, but personally, deeply. It needs a reason to keep going that lives in the gut and the heart, not just the mind. And that brings us inevitably to a question that transcends biology entirely. If we change the human body and brain enough to survive on Mars, if we modify genomes, enhance nervous systems, integrate technology, at what point does the thing we have created stop being human? And does that question even have a meaningful answer?
Or is [music] it like so many of the best questions in science less a problem to be solved and more a horizon to walk toward? Philosophers have wrestled with versions of this for centuries. The ship of Thesius. If you replace every plank of a ship one by one, is it still the same ship? We replace most of ourselves over the course of a lifetime. Our brains rewire themselves continuously with every experience we have. We are already in a biological sense not the same person we were 10 years ago. Maybe the question is not whether Mars humans will still be human. Maybe the question is what kind of humans they will be and whether the thing that defines us, the curiosity, the drive to understand, the capacity for love and grief and wonder, whether that survives the crossing, I believe it does. More than that, I believe it might be those very qualities more than any genetic modification or technological augmentation that are the most essential survival tool for a Mars mission. The capacity to find meaning in difficulty, to build community under pressure, to look at a barren red landscape and see not desolation but possibility. That is after all what humans have always done. But the practical question of how we get people there safely, what we do to the body, what we do to the brain, what we accept and what we refuse in the process of adaptation, those are questions we will need to answer. and we will need to answer them together as a civilization, not just as scientists. If you made it this far, [music] then this channel is for you. Don't forget to subscribe to the channel and give a like. Every week, we go deeper into the questions that matter most and brings you back changed.
So, be part of our community. Now, let's dream for a moment. Not the cautious, careful kind of dreaming that stays safely inside the boundaries of what we already know. The big kind. The kind that looks at an entire planet, cold, barren, radiation soaked and silent, and asks not, "Can we survive there?" But something far more audacious, can we make it home? Terraforming. The word itself sounds like something pulled from the pages of a science fiction novel.
And for most of human history, that is exactly where it lived. But in the last few decades, something remarkable has happened. The concept has migrated slowly, [music] carefully, with enormous caveats from the realm of imagination into the realm of serious scientific inquiry.
Researchers at NASA, at universities around the world, and at private institutions are now publishing peer-reviewed papers on the theoretical mechanics of planetary transformation.
And what they are finding is simultaneously more possible and more difficult than almost anyone expected.
Here is the core challenge. Mars lost the two things that made Earth habitable. its magnetic field and its thick atmosphere billions of years ago.
The magnetic field died when the planet's iron core cooled and solidified, shutting down the dynamo effect that generates a global magnetic shield. Without that shield, the solar wind, a constant stream of charged particles flowing outward from the sun, gradually stripped away the Martian atmosphere over hundreds of millions of years. What remains today is less than 1% of Earth's atmospheric density. Not enough to breathe, not enough to retain meaningful heat, not enough to block the radiation hammering down from above. To make Mars truly habitable, not just survivable inside pressurized habitats, but genuinely livable on its surface, you would need to reverse both of those losses, or at least compensate for them.
Let's start with the atmosphere. because that is where the most concrete scientific proposals exist. Mars is cold, brutally, lethally cold for most of its surface most of the time. The average temperature is around -60° C.
[music] But cold and warm are in planetary terms partly a function of atmospheric pressure and the greenhouse effect. Earth is as warm as it is, not just because of its distance from the sun, but because its atmosphere traps heat. Carbon dioxide, methane, water vapor, these are all greenhouse gases.
And they function like a blanket wrapped around the planet, preventing heat from radiating away into space as quickly as it arrives. Mars actually has significant reserves of carbon dioxide frozen in the polar ice caps and potentially locked in the soil and subsurface rock. Early terraforming proposals, including work by scientist Christopher McKay and others going back to the 1980s and 90s, suggested that if you could release that frozen carbon dioxide by heating the poles, perhaps using orbital mirrors to focus sunlight on them, you might trigger a runaway greenhouse warming effect. Warmer temperatures would release more carbon dioxide. More carbon dioxide would trap more heat. A self-reinforcing cycle that could over centuries raise the average surface temperature enough for liquid water to exist. It sounds elegant, but a 2018 study led by Bruce Jakosski of the University of Colorado Boulder and Christopher Edwards of Northern Arizona University delivered a significant reality check. After carefully mapping all known and estimated reservoirs of carbon dioxide on Mars, polar ice, atmospheric reserves, minerals that could potentially release the gas if heated, they concluded that even liberating every accessible source would only approximately double the Martian atmospheric pressure. still less than 2% of Earth's, nowhere near enough to breathe, nowhere near enough for liquid water to be stable across most of the surface. The carbon dioxide simply is not there in sufficient quantities to do the job on its own. So where does that leave us? With a more complicated, more ambitious, more genuinely staggering picture. One that almost certainly requires not years or decades, but centuries. And that depends not just on physics and chemistry, [music] but on biology. Some researchers have proposed introducing engineered microorganisms to Mars. Organisms specifically designed to thrive in the Martian environment and produce powerful greenhouse gases as metabolic byproducts. methanogenic archa for instance, microbes that produce methane could potentially be engineered to survive in Martian soil and begin pumping methane into the atmosphere, a gas with a greenhouse warming potential far higher than carbon dioxide.
Synthetic biology, the field dedicated to designing and building new biological systems with specific functions, has advanced to the point where this kind of engineering is no longer purely theoretical. It is an active area of research. Though the gap between laboratory proof of concept and planetary scale deployment remains enormous. Others have proposed manufacturing and releasing artificial greenhouse gases compounds called perluocarbons that are extraordinarily potent greenhouse agents and do not exist naturally on Mars. The idea is that a fleet of chemical factories on the Martian surface or in orbit could produce these compounds continuously, gradually thickening and warming the atmosphere over decades. The energy requirements would be staggering. The timeline would be multigenerational.
But the physics at least is not obviously impossible. And then there is the magnetic field problem which is harder, much harder. [music] Without a regenerated planetary magnetic field, any atmosphere you build will simply be eroded away by the solar wind over geological time scales. You would be pouring water into a bucket with a hole in the bottom. Some scientists have proposed placing a large magnetic shield, an artificial dipole magnet at the Mars L1 Lraange point, a gravitationally stable position between Mars and the sun where an object [music] can remain in a fixed position relative to both. A powerful enough magnet there could theoretically deflect enough of the solar wind to [music] significantly reduce atmospheric erosion. NASA scientist Jim Green and colleagues published a paper in 2017 proposing exactly this, estimating that within years of deploying such a shield, the Martian atmosphere could begin to thicken naturally as sublimating carbon dioxide accumulated faster than it was being lost. It is a breathtaking idea.
It is also well beyond current technological capability.
>> [music] >> The magnet required would need to generate a field of roughly one or two Teslas across a structure of planetary scale. The engineering challenges are immense, but the concept is physically sound and concepts that are physically sound have a way eventually [music] of becoming engineering projects. What all of this tells us is that terraforming Mars, true complete terraforming, transforming it into a world where humans can walk outside without a suit and breathe freely is not something that will happen in our lifetimes. [music] It is not something that will happen in our grandchildren's lifetimes.
We are talking about a process measured in centuries at minimum and more realistically in millennia. It is a project for a civilization, not a generation. But here is the thought that I find genuinely moving about that fact.
We are the generation that begins it.
Every great cathedral [music] in human history took longer to build than the lifespan of the people who laid its first stones. The builders of NRAAM de Paris did not live to see it completed.
They laid foundation, raised walls, carved stone, knowing that hands other than theirs would finish the work. They did it anyway because the act of building something larger than yourself, something that will outlast you by centuries, [music] is itself one of the most deeply human things there is. A terraformed Mars would be humanity's greatest cathedral.
>> [music] >> a 2 century, 5 century, thousand-year project of planetary transformation. A gift from us to people who do not yet exist on [music] a world they will call home. But before we get carried away by that vision, we need to sit with an uncomfortable question, one that the scientific community is actively [music] debating, and that deserves more public attention than it currently gets. Should we terraform Mars at all? This is not a trivial objection. It connects to one of the deepest unresolved questions in all of astrobiology.
Is there life on Mars right now? Not ancient fossil evidence of life, though that would be extraordinary enough, but living, active, present tense [music] life. Microbial communities in liquid water beneath the surface. Organisms clinging to existence in the chemically reactive soil. Life we have not yet found. [music] Not because it isn't there, but because we haven't looked in the right place with the right tools.
[music] The tentative radar evidence for a subglacial liquid water lake beneath the south polar ice cap, first reported by the Marsis radar on Mars Express in 2018, while subsequently complicated by additional research, has not been definitively ruled [music] out. The detection of methane in the Martian atmosphere observed by both the Curiosity rover on the surface and the European Space Ay's Trace Gas Orbiter from orbit remains unexplained.
Geological processes can produce methane and that is the most scientifically conservative explanation, but so can biology and we do not yet know which it is. If there is life on Mars, even microbial, even barely hanging on at the edge of what biology can sustain, then terraforming the planet raises an ethical question of almost cosmic weight. Do we have the right to transform an inhabited world to make it suitable for us at the potential cost of whatever already lives there? We would be in a very real sense committing the first act of interplanetary ecological destruction. Some scientists, including the late Carl Sean, argued that if Mars is lifeless, we should terraform it.
That turning a dead world into a living one is a profoundly moral act, an expansion of the biosphere of the universe. Others, including Christopher McKay himself, who helped develop some of the earliest terraforming proposals, have argued that if Mars harbors life, that life's right to its world supersedes our desire for a second home, and that in such a case, we should instead focus on understanding Martian life rather than overwriting it. This debate is not academic. As our missions to Mars become more capable and more numerous, the question of planetary protection, preventing both forward contamination of Mars by Earth organisms and backward contamination of Earth by potential Martian organisms, becomes increasingly urgent and increasingly difficult. Every rover we land carries sterilization protocols designed to reduce microbial contamination. But perfect sterilization is essentially impossible. And as human missions which cannot be sterilized the way robotic spacecraft can draw closer the contamination challenge becomes existential, we may before we ever set foot on Mars need to decide as a civilization what kind of relationship we want to have with that world.
Conquerors or guests, transformers or learners, both paths are available to us. And the choice we make will say something profound about who we are.
Now, I want to bring everything together because we have traveled a long way in this conversation.
From the surface of Mars under that butterscotch sky, all the way down to the molecular machinery of individual cells, through the labyrinthine corridors of the human brain, across the psychological landscapes of isolation and meaning, and out to the civilizational time scales of planetary transformation. And I want to offer you a synthesis. Not a conclusion because this story has no conclusion yet and may not for centuries, but a synthesis of what all of this taken together actually means. The central insight is this. The question of whether humans can live on Mars is really a question about what humans are. And the answer, the honest, scientifically grounded, philosophically rich answer is that humans are not a fixed thing. We never have been. We are a process, a conversation between biology and environment that has been going on for 4 billion years, producing organisms of increasing complexity, increasing adaptability, and in the last blink of geological time, increasing self-awareness. For the first time in the history of life on Earth, one of its products is capable of consciously directing its own evolution, of reading its own genome and asking deliberately what it might want to change, of looking at the threats posed by a new environment and engineering solutions rather than waiting for random mutation and natural selection to stumble upon them across millions of generations.
That is breathtaking. It is also frightening because power without wisdom is one of the oldest tragedies in human experience. And the power to modify human biology to change what we are at the most fundamental level requires a wisdom that we are still developing. A global conversation about values, about rights, about what we owe to future generations and to the living things that share this universe with us. That conversation needs to happen in public loudly and honestly, not just in laboratories and space agency boardrooms. But here is what fills me with something close to awe when I sit with all of this. We are made of stardust. Every atom of carbon in your body was forged in the nuclear furnace of a star that died before our son was born. The iron in your blood was scattered across space in a supernova explosion billions of years ago. You are not separate from the universe looking at it from outside. You are the universe looking at itself. A temporary miraculous arrangement of ancient stellar material that somehow became capable of curiosity, of love, of grief, of wonder. And now that arrangement of stardust is looking at a red dot in the night sky and asking what would it take?
What would we need to become? That question is not born from arrogance. It is born from the same impulse that drove the first humans to cross land bridges into unknown continents to build boats and sail beyond the horizon to look up at the moon and refuse to accept that it was unreachable. It is the impulse that defines us more than any single biological trait, more than our intelligence, more than our language, more than our opposable thumbs. We reach the road to Mars is not a road of hardware alone. It is not just rockets and life support systems and radiation shielding, though all of those matter enormously. It is a road of biological discovery, of understanding ourselves at levels of depth we have barely begun to explore. It is a road of psychological honesty, of reckoning with what the human mind needs to thrive rather than merely survive. It is a road of ethical seriousness, of deciding collectively what changes to our own nature we are willing to embrace and what lines we are not willing to cross. And it is a road of patience, of accepting that the most meaningful things, the things that last, the things that matter across centuries are not built quickly. They are built carefully, stone by stone, cell by cell, generation by generation. The version of humanity that eventually walks freely on the surface of Mars, breathing air they have helped to manufacture under a sky they have helped to thicken. on a world they have chosen to make home. That version of us will carry something forward from this moment, from this conversation. From every scientist who ran an experiment, every engineer who solved a problem, every philosopher who asked an uncomfortable question, every person who looked up at a red star and felt the pull of it in their chest. They will carry the curiosity, the wonder, the refusal to accept that the horizon is a boundary rather than an invitation.
And somewhere impossibly far in the future, a child will be born under a Martian sky. They will look up at night and see a bright blue star, our Earth, our pale blue dot, and they will feel about it exactly what we feel about Mars. Distant, beautiful, mysterious.
and they will wonder that is the most human thing of all and it will survive the crossing. I am certain of it. If this kind of exploration is what you come here for, then please make sure you are subscribed to this channel. Hit that bell so you never miss a new video. And I want to know if you could be on the first human mission to Mars, knowing everything we have talked about today, [music] knowing the risks and the sacrifices and the uncertainty, would still you go? I want to read your answers [music] because this conversation does not end here. It never ends. The universe is too large and we are [music] too curious.
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