Did Life Come From an Asteroid?

[00:00:00]On the morning of September the 24th, 2023, something fell out of the sky over Utah and did not burn. It came down under a parachute onto a stretch of military desert and a recovery crew walked out to meet it.

[00:00:16]Slowly in masks and gloves, the way you approached something you were terrified of breaking. Inside that capsule was 121 g of an asteroid called [music] Benu, 4 oz. a chocolate bars worth of rock.

[00:00:32]It had never touched the earth. That was the entire point. Because for 50 years, we have been asking whether life came from a rock like this one. And every [music] time we tried to answer, we found we had already ruined the evidence just by picking it up. This time we didn't. What came out of that capsule contained very [music] nearly everything a living thing needs and one number that says it wasn't the answer.

[00:01:00]To understand why 4 oz mattered so much, you have to understand the problem it was built to solve. In September 1969, a fireball broke apart over the state of Victoria in Australia and scattered black fragments across a town called Merchesen. People found pieces in paddocks and on driveways. It became one of the most valuable [music] rocks in the history of science.

[00:01:27]Because when chemists took the merch meteorite apart, they found it loaded with organic chemistry.

[00:01:35]Amino acids, the things proteins are built from, the stuff of life inside [music] a rock that had fallen out of space. The implication was enormous. And there was one problem with it, and the problem [music] never went away.

[00:01:51]Merchesen landed in a paddock, in soil.

[00:01:54]On a planet whose every surface [music] is smeared with bacteria, with pollen, with fingerprints, with the amino acids of everything that [music] has ever lived here. So every time somebody found something extraordinary inside Merchesen, another scientist could ask the obvious deadly question, "How do you know that came from space? How do you know it isn't just Australia?

[00:02:20]That question haunted [music] this field for half a century. As Danny Glavin, who studies these samples at NASA Godard, put it, "The clues are so minuscule [music] and so easily destroyed by exposure to Earth's environment." So, somebody had a genuinely audacious [music] idea. Stop waiting for the rock to come to us. go out and catch one before Earth can touch it.

[00:02:47]The spacecraft was called Osiris Rex.

[00:02:52][music] It launched in 2016, spent 2 years crossing empty space to [music] reach Bennu, then two more circling a rock barely 500 m wide, looking for somewhere [music] to touch. In October 2020, it reached out an arm and kissed [music] the surface for 6 seconds. And the surface did something nobody expected.

[00:03:15]The spacecraft sank in [music] like a ball pit, like the asteroid was barely holding itself together.

[00:03:23]Then it [music] turned around and came home. The team needed 60 g. They got 121.6, [music] the largest asteroid sample ever collected. And then gloriously, the box got [music] stuck. Two fasteners jammed and some of the most sophisticated engineers on Earth spent 3 months designing [music] new tools to open a jar. When it finally opened, this is what was inside. 14 [music] of the 20 amino acids that life on Earth uses to build proteins. All five nuclear bases, adinine, [music] cytosine, guanine, thymine, uricil, the letters of DNA [music] and RNA. Not some of them, all of them. ammonia in exceptional abundance, [music] firmaldahhide.

[00:04:13]Put those two together in the right conditions and they build amino acids [music] on their own. Then sugars, ribos, the R in RNA, and glucose, [music] the sugar your cells are burning to watch this. Glucose had never been found in [music] an extraterrestrial sample before. Which means, as the scientist who led that work put it, every component [music] needed to form RNA is present in Bennu. There was stranger [music] material, too. A soft translucent polymer, a kind of space plastic never seen [music] before in a space rock. And through all of it, salt.

[00:04:54]11 minerals that only form when [music] salty water evaporates slowly over thousands of years. That is not a dry rock. That is the residue of pools [music] of water drying out with the entire chemical inventory of life dissolved in them. A broth.

[00:05:13]So did life come from an asteroid?

[00:05:17]Here the [music] question has to be taken apart because it is really two questions wearing the same coat. The first did life's [music] ingredients come from asteroids?

[00:05:28]That case is strong and getting stronger.

[00:05:32]The young earth was bombarded [music] and every one of those impacts was a delivery. Material like Bennu was [music] arriving by the ton. NASA's own conclusion is careful and remarkable.

[00:05:45][music] The findings suggest the conditions necessary for life were widespread across the early solar system.

[00:05:52]The second question is the one people actually mean. Did life itself come from an asteroid? [music] Did something alive ride down on that?

[00:06:01]The sample says nothing whatsoever.

[00:06:03]There is no evidence of life in Bennu.

[00:06:06]No cells, [music] no fossils, no biology, only chemistry. And there's a fair objection which deserves its best case. Earth may not [music] have needed the post.

[00:06:18]In 1953, Stanley Miller [music] put a spark through a flask of simple gases and made amino acids in under a week.

[00:06:27]Hydrothermal [music] vents turn out to be chemical factories in their own right. Earth could plausibly have [music] cooked all of this for itself.

[00:06:36]So, the honest picture is probably both.

[00:06:40]A planet already [music] making its own ingredients, being pelted with more from the sky. But notice [music] what neither answer touches. Ingredients are not a living thing. A pile of bricks is not a house. You can have every amino acid, every nucleobase, ribos, phosphate, glucose, the complete set, and have absolutely nothing alive. Something [music] has to happen to the parts. And when we looked closely at Bennu's parts, they were missing the one thing life cannot work without. Amino acids are handed. The same molecule, same atoms, same bonds can be built in two mirror versions [music] like your left hand and your right. Identical and not [music] interchangeable.

[00:07:31]Make them in a laboratory and you get a 50/50 mixture every time. Nature has no reason to prefer one. But life on Earth is not 50/50.

[00:07:43]Life is left-handed. Almost every [music] protein in your body in every living thing on this planet is built from left-handed amino acids only. Hand a cell the mirror image and it's useless.

[00:07:58]Nobody knows [music] why. It is one of the deepest unsolved problems in the origin of life. It has a [music] name homocyality.

[00:08:08]And for 50 years, there was [music] a beautiful possible answer sitting inside the Merchesen meteorite. Because in 1997, researchers [music] reported that Merchesen's amino acids were not 50/50.

[00:08:22][music] There was an excess of left-handed ones, and isotopes, they argued, showed that excess was genuinely extraterrestrial.

[00:08:31]If that were true, it is a gorgeous story. Space [music] didn't just deliver the parts. Space delivered the bias.

[00:08:40]The universe handed the early Earth a deck already stacked to the left and life simply played the hand it [music] was dealt. That claim was fought over for decades.

[00:08:51]Other chemists said contamination Australia again. Others an artifact of the measurement. And the argument could never be settled because the rock had been sitting in a [music] paddock since 1969. Then we caught a clean one. Benu's amino acids are 50/50.

[00:09:11]Equal left and right, no excess, no stacked [music] deck, nothing. Which means that if Bennu is anything to go by, the amino acids raining onto the early Earth arrived unhanded.

[00:09:25]Space did not give us our left-handedness.

[00:09:28]Whatever turned life left happened here, and in February of this year, it got stranger. A team at Penn State measured the isotopes in Benu's glycine, expecting the textbook story made in warm water [music] inside the parent asteroid.

[00:09:46]It wasn't. Benu's glycine looks like it formed in ice, frozen in the dark under radiation.

[00:09:55]Their results, one author [music] said, flipped the script and set against Merchesen. The isotopes didn't match at all. Those two [music] rocks built their amino acids in different regions of the solar system by different chemistry.

[00:10:11][music] So did life come from an asteroid carries a hidden assumption. An singular as though there were one delivery, one recipe, one origin. There wasn't. There were many and they don't agree with each other. [music] So where does that leave the question?

[00:10:31]Here is what we know. Asteroids carry [music] the ingredients of life, not traces, not hints. Amino acids, every letter of the genetic alphabet, sugars, salts, the lot. [music] And they delivered them to the early Earth in staggering quantity.

[00:10:50]That isn't speculation anymore. We went out and got the receipt. Here is what we don't know. Whether Earth needed the [music] delivery at all or was already making its own. Which pathway actually [music] mattered? Why two rocks from the same solar system tell different stories? And here [music] is what nobody knows. Why life turned left. Whether anything alive has ever ridden a rock between worlds, and why we so far see life only here and nowhere else, which the scientist who led this mission science calls the truly tantalizing question. The rock brought the parts.

[00:11:29]Something here assembled them [music] and chose a hand and started. We still don't know what that something was.

[00:11:35][music] What do you think it was? And that is where I will leave it. And if there is a mystery you would love to see [music] untangled, tell me. Until the next one.

[00:11:48][music]