The Secret Buried Beneath Mars | Cosmic Journeys - Mars: World That Never Was

[00:00:04]There is a region on Mars, roughly the size of Australia, that rises high above the surface of the planet.

[00:00:13]Three of the largest volcanoes in the [music] solar system line up to guard its western flank.

[00:00:21]To the east, a vast canyon, six to seven times deeper than the Grand Canyon, cuts into the barren Martian plain.

[00:00:32]This strange region, once so baffling to scientists, recalls the planet's violent past.

[00:00:44]A time long ago when the planet's core erupted, pushing molten rock to the surface.

[00:00:52]It's part of a larger story, a planetary tragedy, in which Mars began its descent into the cold, dry, and lifeless state that we see today.

[00:01:04]We are now scouring its surprisingly complex surface for clues to the events that long ago doomed the red planet, Mars.

[00:01:23]Since the early 1960s, we've tried [music] 46 times to send spacecraft to Mars across the 55 million kilometers of its closest approach to Earth.

[00:01:37]Over half failed at launch or upon arrival.

[00:01:42]The rest flew around the planet, snapping pictures, recording data.

[00:01:52]Or they landed to test its soil and rocks.

[00:01:58]And crawl around [music] its canyons and craters.

[00:02:02]These probes may one [music] day pave the way for human explorers who will dig deeper still in search of answers to our most [music] pressing question.

[00:02:14]Did Mars, at some point long ago, develop far enough for life to arise?

[00:02:21]If so, does anything still live within Mars' [music] dusty plains, beneath its ice caps, or somewhere underground?

[00:02:35]Mars does not give up its secrets easily.

[00:02:39]Over the years, that has led observers on this planet to jump to all sorts of conclusions.

[00:02:46]In the year 1877, the Italian astronomer Giovanni Schiaparelli noted markings on Mars' surface, a lattice work of lines.

[00:02:57]He called them canali in Italian, meaning channels in English.

[00:03:03]Schiaparelli began to sketch them and name them, connecting them in a vast global network.

[00:03:10]Over a 15-year period, beginning in 1894, the American astronomer Percival Lowell closely examined these features.

[00:03:21]He saw a remarkable [music] drama unfolding on our neighboring planet.

[00:03:27]In his view, Schiaparelli's channels were artificial canals, designed perhaps to carry melting snow from the poles to the dry interior.

[00:03:39]After all, on Earth, the Suez Canal had been open since 1869.

[00:03:46]Construction on the Panama Canal had just gotten underway.

[00:03:51]The Martian canals, Lowell surmised, had been built by a sophisticated society confronting an environmental catastrophe on the grandest of scales.

[00:04:03]Its inhabitants [music] faced an urgent choice.

[00:04:06]Move water across vast arid regions or perish on an increasingly [music] dry planet.

[00:04:14]In a series of three best-selling books, Lowell took his case to the public.

[00:04:18][music] The public responded with some ideas of their own.

[00:04:26]With the means to remake an entire planet, perhaps these Martians were more advanced than humans.

[00:04:34]Some of us began offering schemes for making contact.

[00:04:38]Giant mirrors to flash greetings.

[00:04:42]Light beams.

[00:04:45]Mental telepathy.

[00:04:49]Lowell's vision fell by the wayside in 1964.

[00:04:53]The Mariner 4 spacecraft flew by Mars and got a good look.

[00:04:58]What it saw looked more like the moon than the Earth.

[00:05:03]Three more Mariners followed.

[00:05:05]These missions documented a heavily cratered landscape pocked with huge dormant volcanoes and cut with the deepest and longest canyon in the solar system.

[00:05:17]They saw no traces of life, present or past.

[00:05:23]Then in the mid-1970s, two lander-orbiter robot teams named Viking went in for an even closer look.

[00:05:32]The landers tested the soil for the chemical residues [music] of life.

[00:05:37]All the evidence from Viking told us Mars is dead and extremely harsh.

[00:05:46]The mission recorded Martian surface temperatures from -17°C down to -107.

[00:05:55]We now know [music] it can get even colder than that at the poles.

[00:06:00]The atmosphere [music] is 95% carbon dioxide with only traces of oxygen.

[00:06:07]And it's [music] extremely thin with less than 1% of the surface pressure of Earth's atmosphere.

[00:06:15]And it's bone [music] dry.

[00:06:17]In fact, the Sahara Desert is a rain forest compared to Mars, where water vapor is a trace gas in the atmosphere.

[00:06:27]On Earth, impact craters erode over time from wind and [music] water and even volcanic activity.

[00:06:35]On Mars, [music] they can linger for billions of years.

[00:06:40]Earth's surface is shaped and reshaped by the horizontal movement of plates that make up its crust, driven by heat welling up from the planet's hot interior.

[00:06:52]At half the width and only 11% [music] the mass of Earth, Mars doesn't generate enough heat to support wide-scale plate tectonics.

[00:07:03]Nor does it have the gravity to hold a thick atmosphere needed to store [music] enough heat at the surface to allow liquid water to flow.

[00:07:14]Nonetheless, some areas that looked to Viking era scientists like craters and volcanic [music] areas were later shown to be riverbeds, lake bottoms, [music] and ocean shorelines.

[00:07:30]If water once flowed on Mars' surface, where did it all go?

[00:07:39]This was the scene at NASA's Jet Propulsion Lab in 2004.

[00:07:44]The twin rovers Spirit and Opportunity had just bounced down on the red planet.

[00:07:52]When the excitement [music] died down, the rovers were set off on one of the most remarkable journeys in the history of planetary exploration.

[00:08:02]Opportunity had come to rest in a small crater near the equator at a spot called Meridiani Planum.

[00:08:11]Here in plain view on a nearby [music] crater wall, its camera revealed exposed bedrock.

[00:08:18]The first ever seen on Mars.

[00:08:21]Not far away, the rover found layered rocks on the face of a cliff.

[00:08:27]On Earth, they typically form as sedimentary layers at the bottom of oceans.

[00:08:35]And at every turn, Opportunity rolled across tiny smooth round pellets.

[00:08:41]They became known as blueberries because they appeared purplish-brown against Mars' rust-colored surface.

[00:08:49]Initially thought to be volcanic in origin, they turned out to be iron-rich spherules of the type that form within cavities in the mud at the bottom of an ocean.

[00:09:03]Drilling into rocks, the rover inserted a spectrometer to read the mineral content.

[00:09:09]The readings showed significant amounts of sulfate salt, a tracer for standing water.

[00:09:18]That wasn't all.

[00:09:20]Spirit's broken wheel, dragging behind it, exposed soils saturated in salt.

[00:09:28]Clearly, there was once water on Mars' surface.

[00:09:32]But how long ago?

[00:09:34]And if there's anything left, where would you find it?

[00:09:41]One possible answer, the North Pole.

[00:09:45]From orbit, this region seemed to be covered in frozen CO2, what we call dry ice.

[00:09:52]But was there water ice below the surface?

[00:10:02]Enter Phoenix, a lander that touched down near the North Pole in early 2008.

[00:10:18]Radar readings from orbit, taken by the Mars Express mission, hinted at the presence of ice just below the surface.

[00:10:26]The Phoenix lander's descent thrusters blew away the top layer of soil, allowing its camera to snap pictures of what looked like ice.

[00:10:37]Scientists instructed the robot to conduct a simple experiment.

[00:10:41]Reach out and dig a trench, then watch what happens.

[00:10:46]As expected, lumps of white stuff appeared.

[00:10:50]A couple of days later, it was gone.

[00:10:53]Vaporized.

[00:10:55]That means it can't be salt or frozen CO2, which is stable in the cold dry temperatures of the Martian Pole.

[00:11:04]So, it had to be water, the first ever directly seen on Mars.

[00:11:13]There are indications that the North Pole was actually warm enough [music] in the recent past for water ice to become liquid.

[00:11:21]The Mars [music] Reconnaissance Orbiter, or MRO, used radar pulses to peer beneath the surface of the ice cap.

[00:11:29]These data revealed that the ice, just over a mile thick, formed in a succession of layers >> [music] >> as the climate alternated between warm and cold.

[00:11:42]Our planet avoids mood swings like this, >> [music] >> in part because its spin is stabilized by a massive moon.

[00:11:50]Mars spin is not, so it can really wobble with the pole tilting toward the sun for long periods.

[00:12:00]New observations by the MRO spacecraft show that these wobbles can [music] lead to dramatic releases of CO2 and warming periods due to an increase in the greenhouse effect.

[00:12:14]The ice now detected below Mars surface is a remnant of a much earlier time.

[00:12:22]The thinking is that not long after its birth, the planet's molten interior would have spewed out enough gas to form an atmosphere.

[00:12:32]Carbon dioxide and water vapor began to trap heat from sunlight.

[00:12:41]Temperatures rose high enough to allow liquid water to flow on the surface, creating myriad rivers, ponds, lakes, and oceans.

[00:12:55]Evidence of this thicker atmosphere landed literally in Opportunity's backyard.

[00:13:01]The rover spied a strange bluish rock, a nickel-iron meteorite named Block Island.

[00:13:09]Streaking through a thin atmosphere, this massive chunk of metal should have been obliterated on contact.

[00:13:16]Instead, its fall was likely slowed and its impact softened by a much thicker atmosphere.

[00:13:24]What then caused the atmosphere and the water to disappear and the planet to grow cold and dry?

[00:13:35]The answer comes from data recorded by the Mars Global Surveyor just after it went into orbit in 1997.

[00:13:44]Its instruments detected the presence of a weak magnetic field emanating from the planet.

[00:13:50]A reading that scientists eagerly compared to that of Earth.

[00:13:56]Our planet's magnetic field is generated by molten rock deep in its core that rises and falls into a vast region below the outer crust called the mantle.

[00:14:09]The rising and sinking motion within, combined with the spinning motion of the planet, generates a strong magnetic field.

[00:14:19]You can trace this field back to Earth's early years when large amounts of heavy elements such as iron sank [music] into its core.

[00:14:28]Radioactive decay began to generate heat and the planet's mass is large enough to hold it in.

[00:14:36]Earth's magnetic field extends far enough out into space to deflect the wind of high-energy solar particles.

[00:14:45]Without a similar electromagnetic [music] deflector shield on Mars, solar radiation lashed the planet gradually stripping it of its atmosphere.

[00:14:56]What water Mars had would have vaporized into space or frozen underground.

[00:15:03]However, there is evidence that at one time >> [music] >> Mars did have a robust magnetic field.

[00:15:10]Rocks in some of the older craters bear a strong imprint of this field while newer craters indicate a much [music] weaker field.

[00:15:20]What happened to it?

[00:15:23]The answer lies deep in Mars' past, in events so powerful they are still written on the landscape.

[00:15:36]This is a simple elevation map of Mars' surface from data gathered by the Mars Odyssey spacecraft.

[00:15:44]The South Pole, colored in red and orange, is piled high with ice.

[00:15:50]Moving off these southern highlands, we make our way north.

[00:15:55]The landscape [music] is pocked with craters.

[00:15:58]The largest and oldest ones have faded, their edges softened by wind-blown dust.

[00:16:04]Moving up along the equator, we pass into a region called Tharsis, based on a biblical name for the western edge of the known world.

[00:16:15]On the edge of this vast high-altitude plateau, is a series of enormous volcanoes.

[00:16:22]Ascraeus Mons, 18 km high.

[00:16:28]Arsia Mons, 16 km.

[00:16:33]Pavonis Mons, 14 km.

[00:16:37]Just beyond is the largest volcano in our solar system, Olympus Mons, 25 km in elevation.

[00:16:47]The thinking is that the Tharsis region bulged out when a giant dome of magma pushed up from the planet's core.

[00:16:56]The volcanoes grew large because Mars lacks the constant shifting of crustal plates that on Earth leads to chains of smaller volcanoes, like the Hawaiian Islands.

[00:17:12]Just to the east is the great Valles Marineris, named for the Mariner 9 mission that found this vast [music] gash in the Martian landscape.

[00:17:22]It's about 4,000 km long and up to 200 km wide.

[00:17:29]On Earth, Valles Marineris would stretch from Los Angeles all the way to the Atlantic [music] coast.

[00:17:40]If you went to Valles Marineris, you'd see dust [music] devils sweeping along the plains above it and dust blowing up the canyon walls.

[00:17:59]Here's a realistic rendering of data captured by spacecraft.

[00:18:04]Giant landslides have [music] caused the walls to slump off and pile onto the valley floor.

[00:18:11]Feeding into the valley, a maze of side channels.

[00:18:15]Scientists think these and other tributary [music] features were formed when underground water flowed into the main basin and the land above collapsed.

[00:18:27]Wider parts of the canyon are regarded as possible landing sites for a manned mission.

[00:18:33]They offer flat surfaces and possible access to [music] liquid water that may remain below the surface.

[00:18:41]The theory is that Valles Marineris formed when the planet began to cool.

[00:18:48]Its sides were pulled apart as the Tharsis plateau, just to the west, began [music] to rise up.

[00:18:55]That chain of events is now being linked to a much larger planetary event.

[00:19:02]What one scientist called the defining moment in Mars' history.

[00:19:12]Travel north down the slopes of Mars' great volcanoes.

[00:19:18]The elevation [music] drops as we move across what appears to be an immense ocean colored here in blue.

[00:19:26]With this so-called Borealis Basin [music] in the north and the high elevations of the south, Mars is a lopsided planet.

[00:19:35]In fact, [music] there is a difference of about 30 km in the thickness of the crust of these two regions.

[00:19:43]Here's the reason.

[00:19:45]Early on, when the solar system was young, Mars was hit by at least 15 large asteroids.

[00:19:55]Scientists have linked these events to a time around 3.9 billion years ago known as the Late Heavy Bombardment, when rock samples from the Apollo landings show that our own moon was seriously pummeled.

[00:20:15]One theory holds that these impacts heated the outer subsurface layer of the planet, Mars' mantle.

[00:20:22]That prevented molten rock in its core from rising up and caused the crust to thicken.

[00:20:28]This had the effect of shutting off Mars' magnetic field, exposing the planet to damaging solar winds and over time turning it into a wasteland.

[00:20:44]There are other theories that explain the disappearance of Mars' magnetic field and its atmosphere.

[00:20:52]What's certain is that at some point early in its history, the red planet [music] grew increasingly desolate.

[00:21:01]The Martian landscape we see today is replete with coded signals from these early times, ancient riverbeds [music] and lake bottoms, flood plains, and volcanic cones, as well as the battering it received from impacts.

[00:21:20]But, is Mars a dead world?

[00:21:24]Maybe.

[00:21:25]Maybe not.

[00:21:28]An infrared telescope on Hawaii's Mauna Kea volcano was trained on Mars over several years.

[00:21:36]Astronomers used a spectrometer to split the light into its individual wavelengths to identify chemical fingerprints in the atmosphere.

[00:21:45]They found the signature of methane [music] gas in amounts that change from place to place.

[00:21:52]Because methane should disappear quickly in Mars' atmosphere, [music] there must be some source that constantly replenishes it.

[00:22:01]That source could amount to nothing more than the chemical reactions in Mars' crust.

[00:22:06]Or, it could be biological in nature.

[00:22:09]Perhaps microbes alive and well in heated pools underground.

[00:22:16]So far, neither the satellites flying over Mars nor the robots on the ground have turned up anything close to clear proof of life.

[00:22:29]It may take the searching eyes, flexible minds, and nimble fingers of human explorers to find that buried treasure, if it exists.

[00:22:41]In the meantime, we are finding that even if Mars is dead, it's certainly not dull.

[00:22:48]Mars has nowhere near the dynamism [music] of Earth with its oceans, atmosphere, volcanism, and shifting continents.

[00:23:06]But it does do some fascinating things.

[00:23:09]If you take an atmosphere, however tenuous, add heat from the sun, you get the renowned dust devils of Mars.

[00:23:20]With no trees to [music] hold the soil down, landslides are common.

[00:23:27]The Mars Reconnaissance Orbiter has returned images showing that Mars is actively remaking its surface.

[00:23:34]Not in canals built by the Martian engineers of Percival Lowell's imagination, but in sand dunes shaped by the wind, and in landscapes molded by a gradually changing climate.

[00:23:51]Some scientists have even turned up hints of low-level plate tectonics.

[00:24:00]Whether or not [music] we ever find life forms on Mars, we can still marvel at the beauty of our neighboring planet.

[00:24:10]Its surface subtly sculpted over eons of time on a world that never was.

[00:25:03]>> Mhm.