Did NASA find evidence of life in asteroid samples?

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This week, NASA had a huge announcement — scientists studying a sample of the asteroid Bennu, retrieved by the mission OSIRIS-Rex, found the ingredients for life within the sample.

They did not find actual alien life.

Let’s break down this discovery, what it means exactly, whether it could be the product of Earth contamination, and take a look at the bigger picture here.

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What exactly did scientists discover?

Scientists studying samples of a near-Earth asteroid called Bennu were surprised to find within the dust grains the building blocks of life, as well as evidence of a saltwater environment. The question is, what’s the difference between finding the building blocks of life and finding life itself?

All life on Earth is carbon based. As far as we know, carbon is necessary for any life to form. But there are other things we think are necessary for life to form as well. That includes organic compounds, such as amino acids (which create proteins when they link up into long chains). Proteins are key to powering biological functions, and we have genetic instructions on how to arrange amino acids into proteins, thanks to the nucleobases in RNA and DNA.

Well, scientists studying these asteroid samples found 14 of the 20 amino acids used by life on Earth to create proteins. They also found all five nucleobases used by Earth-based life, which are the genetic components of RNA and DNA. Additionally elements and minerals necessary for life, some expected and some unexpected, were present in the sample.

They didn’t find that life had developed on Bennu (more on that later.) The bottom line is that what they discovered gives us hints to the origin of life here on Earth. Let’s dive in.

The chirality of amino acids

There was something very interesting about the amino acids detected within these samples. In very basic terms, amino acids come on two forms that mirror one another, but aren’t identical. Danny Glavin from NASA’s Goddard, who’s leading the sample organics analysis team, used the analogy that it’s like your hands. You have your right hand and left hand and they’re mirror images, but if you try to stack them on top of one another, your thumbs will stick out. As a result, the types of amino acids are called right-handed and left-handed forms.

Life on Earth — all of it — is based on the left-handed amino acid form. We don’t know why, but this is how it is. The hypothesis, then, was that the solar system was biased in favor of this. It’s what scientists have found studying other meteorites as well.

But Bennu showed us something different: an equal mixture of left-handed and right-handed forms. One thought might be many of the meteorites that showed more left-handedness were subject to the stresses of entry into Earth’s atmosphere and were found on Earth. Bennu is an asteroid that’s much too fragile to survive that process, so maybe that plays a role in this difference.

The origin of Bennu, the origin of life?

But there’s more. They also found a large quantity of ammonia, about 100 times the natural level of ammonia in Earth soil. Now, ammonia is an important part of the nitrogen cycle (and biology relies on nitrogen and nitrogen-based compounds). Ammonia can react with formaldehyde, which scientists also found in the Bennu sample. Scientists think that this ammonia was used to form amino acids in the nucleobases.

Ammonia is volatile, which means it evaporates at relatively low temperatures. This high level of ammonia likely means that Bennu, and whatever larger asteroid it likely broke off of, formed near the edges of the solar system, where it was much colder. That’s really the only way the ammonia ice they found would have remained stable, so this gives us a hint of where Bennu originated. This is outlined in the journal Nature Astronomy.

Scientists also discovered traces of 11 different minerals in this sample.

As far as we know, these minerals form when salt water slowly evaporates, leaving salt crystals.

We’ve detected some of these minerals before; sodium carbonates, which are commonly found in dried-up lake beds on Earth, have been detected on Ceres and in the plumes of Enceladus, Saturn’s moon.

They also found elements essential to biology such as phosphorous and sulfur within these briny areas, and these salts may help synthesize organic molecules on the asteroid. These findings are discussed in the journal Nature.

We think that Bennu broke off of a larger asteroid somewhere around 700 million to two billion years ago, and that larger asteroid may have had pockets of liquid water.

Where did this sample come from?

If you are unfamiliar with this asteroid sample, let me give you a quick summary of the OSIRIS-REx mission which returned a pristine sample of the asteroid Bennu to Earth in September 2023.

The mission launched on September 28, 2016 to the near-Earth asteroid Bennu, which makes its closest pass with the Earth every six years (around 186,000 miles or 299,000 kilometers). OSIRIS-REx arrived at Bennu in December 2018 and spent two years studying the asteroid and mapping its surface to find an optimal sample collection site.

On October 20, 2020, the spacecraft briefly touched down on Bennu and collected its sample.

If you’re curious about how the spacecraft returned to Earth, I wrote about it in depth over at The Planetary Society. But on September 24, 2023, the sample return capsule separated from the spacecraft and re-entered Earth’s atmosphere. (The larger spacecraft is continuing onto the asteroid Apophis.)

The container touched down safely at the Utah Test and Training Range, where it was retrieved by scientists and immediately put under a nitrogen purge to ensure the sample contents remained pristine.

It was transferred to a clean room area built specifically for these samples at Johnson Space Center in Houston.

It took awhile to get the sample container open because it was stuck.

Basically two of the fasteners that held the sample container closed were stuck, and scientists couldn’t remove them with approved tools. All work on the OSIRIS-REx sample container was done in a sealed box under a flow of nitrogen. That’s not the easiest situation to work with.

They finally got the sample container open in January 2024.

The goal was to get 60 grams of sample material. The team ended up with 121.6 grams, over twice what they’d wanted.

Is it possible that this sample was contaminated — like Japan’s Ryugu sample?

Contamination is a very real possibility with samples like this — basically, there’s always the question of whether any organics or materials found in the samples could be the result of terrestrial contamination.

It’s especially relevant because scientists working with samples of the asteroid Ryugu from Japan’s Hayabusa2 sample return mission. Basically a lab revealed that they’d found micro-organisms inside a sample from the asteroid. But these weren’t from Ryugu: the lab found that these organisms colonized the sample after it was exposed to the Earth’s atmosphere.

Life is a lot more persistent than you think it is, and it’s incredibly hard to kill all of it. There are bacteria that survive in NASA clean rooms because they’ve adapted to eating the cleaning products. Microorganisms have survived on the outside of the International Space Station since the core module Unity launched in 1998.

So the question is whether the same could be said for OSIRIS-REx’s sample, could what we’re finding be the result of contamination?

It’s unlikely, but we can’t say it’s impossible. OSIRIS-REx samples have been very carefully handled since the sample container touched down. It’s been under a nitrogen purge constantly (nitrogen doesn’t interact with most other things, so it keeps the sample pristine), and samples have been sent to multiple different labs (under nitrogen) that are all having similar findings.

The team went as far as obtaining hydrazine propellant that was used on the spacecraft to ensure that the ammonia that they found in the samples was chemically distinct from rocket and thruster fuel, so they are doing their homework here.

It’s also worth noting that JAXA, the Japanese Space Agency, put out a statement saying that the Ryugu sample was delivered to the lab in a container under a nitrogen purge, similar to the OSIRIS-REx samples. This means that, in their opinion, the sample was likely contaminated in the lab, after the container was opened, and was not sent to the lab with contamination. It’s a bit of pointing fingers in this case, but it’s worth noting that there are no other reports of Ryugu sample contamination as far as I know.

Ok, but I still don’t understand why I should care!

It’s important to note that scientists have found these building blocks for life before on meteorites and in other asteroid sample return missions, like the afore-mentioned Ryugu mission. This is not the first time we’re discovering these.

So then, why is it significant?

Bennu formed around 4.5 billion years ago, as a part of a larger asteroid. If that figure sounds familiar, that’s because scientists think that’s around when our solar system formed. That means that it might be able to give us answers to the big questions: Why are we here? How did life form on the planet Earth?

What we’ve found on Bennu indicates that the building blocks for life on Earth could have come from asteroids similar to Bennu’s parent asteroid. Impacts from asteroids like this could have seeded life on Earth. While material would be burned off the outer surface of a meteorite through the process of entering Earth’s atmosphere, these internal materials would remain intact.

And that’s the key with the Bennu sample — while the Ryugu sample was very much from the surface of the asteroid, the Bennu sample is from further down, from about a half meter under the asteroid’s visible surface. Part of the reason Bennu was such an intriguing asteroid to visit was because it’s a loose rubble-rich asteroid, which means that its surface is basically rocks and pebbles that are barely held together by gravity. Choosing an asteroid like Bennu to sample ensured that we’d be able to dig down deep for the sample without having to drill.

While a loose asteroid like Bennu would never have survived Earth atmosphere entry (due to size and composition), it’s possible the larger asteroid Bennu came from would have been able to.

What’s more, the abundance of these materials in this tiny sample from Bennu indicates that these elements might be abundant throughout the solar system (and possibly other solar systems), and through these asteroids, life may have been seeded on other worlds as well. The analysis of the Bennu sample helps us with our search for life on other worlds.

What’s next?

As scientists continue to study this sample over the next few decades, one question that comes front and center is that if Bennu has the building blocks of life, then why didn’t life form on this asteroid?

It’s a small sample of the asteroid to be sure, but scientists studying the material are confident in saying that Bennu does not support life. It never formed on the asteroid. There are no structural fossils or chemical fossils within the sample. That being said, it is impossible to prove a negative, that Bennu does not support life, but scientists are comfortable saying definitively that it did not form on Bennu.

We don’t know why that is, and scientists are hoping to figure it out with further study.

We’re just getting started with this sample from Bennu. This certainly won’t be the last press conference about this sample. There are multiple labs studying the Bennu sample, but also there’s a lot of the sample left.

There’s well over 100 grams of it still at the lab at Johnston Space Center that can still be requested. Around 7.5 grams are still hermetically sealed, and around 7.5 grams are still in deep freeze, for future generations to request and study.