LOOKING FOR LIFE ON MARS

The Mars 2020 Rover, named Perseverance, is set to launch this month. It will collect rock and soil samples from our red neighbour, which Miché Aaron will be using in her search for organic minerals. She tells Amy Barrett how the presence of these minerals could reveal if there was once life on Mars… WHAT MINERALS ARE THERE ON MARS?

There are silicates, which basically contain silicon and oxygen atoms, along with magnesium, iron or calcium. Depending on the silicate, they can either be arranged in sheets, layered flat, like a flaky pastry; or globular, like people would expect a rock to look. Other minerals we have are iron oxides – the reason why Mars is red. Haematite is one of the most common iron oxides that you’ll see on Mars and on Earth too. We call it haematite because it’s red like blood [the word ‘haematite’ is derived from the Greek for ‘blood’].

Then there are things like sulphates, oxalates and carbonates, and I’m sure there are others that I haven’t named. Carbonate is the one that many scientists want to find, for the same reason that I want to find oxalates: because of the association with life.

WHAT ARE OXALATES?

You actually might be more familiar with them than you think. If you’ve heard of kidney stones, that’s calcium oxalate.

Oxalates are organic minerals, and they’re often associated with living organisms, although they can form through abiotic [non-biological] methods. On Earth, they primarily form through biological processes in plants or animals. So, they have a strong association with life on Earth, and they’re really exciting because they’re known to be stable on the surface of Mars. They can exist in extreme environments. And when I say extreme, I mean environments in which a human wouldn’t thrive for very long, without some sort of mechanism to keep them alive. Think of places like Antarctica, or the Atacama Desert – those are actually two good analogue sites for Martian research.

Oxalates are also high-value targets because they have the potential to preserve biological activity from past and present Mars.

“Oxalates have a strong association with life on Earth, and they’re really exciting because they’re known to be stable on Mars”

SO IF OXALATES ARE FOUND ON MARS, IT COULD MEAN THERE’S LIFE THERE?

Well, not necessarily, because oxalates can also form through this [non-biological] process called diagenesis, which is when a mineral is physically and chemically changed by increases in temperature and pressure, or through hydrothermal [hot water] processes.

On Earth, these changes in temperature and pressure happen after sediments rich in organic matter are deposited and buried. There they are reheated and they experience more pressure, to the point that their molecular structure changes. Then, when they come back up to the surface, it’s in a different form, similar to metamorphic rocks.

Now, we don’t see surface uplifting on Mars because as far as we know Mars doesn’t have tectonic plates. So there is no mechanism for rocks formed through metamorphism, much less diagenesis, to resurface.

Yet we do have metamorphic rocks on Mars, and can witness diagenesis by analysing rock layers along the sides of craters. That, we believe, is due to meteorite impacts because that is the only thing that can cause that high amount of pressure and heat to do that process. These meteorites, or to be more specific, these carbonaceous chondrites, contain an acid called carboxylic acid. That carboxylic acid actually bonds with other substances to create oxalates.

So, if I were to detect oxalates on Mars tomorrow, would I be able to say that, yes, there is life on Mars right now, or there was life on Mars? That there was vegetation? That there were mushrooms? No, I couldn’t, because whenever I collect that information, it’s hard for me to determine how they [the oxalates] formed.

HOW DO YOU DETECT MINERALS ON MARS?

I use something called remote sensing, which is where an instrument collects information from the surface of the planet in the absence of physical contact. I use infrared spectroscopy. Spectroscopy is the study of light, and how light interacts with an object. Infrared can produce vibrational properties when it interacts with a mineral’s molecular structure. The distinct patterns made by each mineral group are like a fingerprint that we can use to help identify the minerals on Mars.

Mars is pretty far away from Earth, so it takes some time for large quantities of data to get transferred here. And when that happens, we generally get raw data, which is unprocessed, and can often contain artefacts – basically things that can inhibit a person from properly analysing the data. So, for example, with my datasets I often have to make atmospheric corrections, because unfortunately Mars is very, very dusty. That dust interferes with our data.

In-situ [on-location] spectroscopy with the rovers is actually the best way to analyse rocks on a different planet, as there is no atmospheric interference. I’m not currently using rover data because I’m still relying on satellite imagery to get a good idea of which location has oxalates. I know one of the locations is Jezero Crater, which is where the Mars 2020 Rover, Perseverance, is going to land. Perseverance is scheduled to launch this month, on 20 July. Do you understand the significance of that day?

I DON’T.

That was the day that Apollo 11 landed on the Moon. So last year, we had the 50th anniversary for the Moon landings. I just think that it’s really cool that was the date picked for it.

HOW DID YOU COME TO BE LOOKING FOR EVIDENCE OF LIFE ON MARS?

My grandparents took me to space camp at the Space Center in Houston every summer from the age of around eight until I was 13 and I aged out. That was when I was first enamoured by anything related to space. We built rockets, we met astronauts, we learnt about the Space Shuttle programme – I still tear up whenever I see the Space Shuttle launch on video. And even though

MICHÉ AARON After studying planetary geology at Wesleyan University, Miché started a master’s in geographic information systems (GIS) at Sam Houston State in Texas. After getting her master’s, she began working at Carnegie Geophysical Laboratory, researching oxalates. From there, she got connections with people at Johns Hopkins Applied Physics Laboratory and progressed her research using remote sensing. She is now studying for a PhD at Johns Hopkins. Miché went viral on Twitter when she posted a list of resources to help underrepresented students get information on degrees, scholarships, fellowships, funding applications and mentoring opportunities. She also helped set up the Woman of Color Project, a programme that helps women of colour in STEM apply to and thrive in grad school.

“When learning about space exploration, all I saw were white men. I don’t think I was even exposed to Mae Jemison”

we basically did the same stuff every summer, at the end of the programme I’d always tell my grandparents, “I want to work at NASA when I grow up.”

I was just fascinated by the stuff that’s out there, the galaxies, planets, stars… My grandparents got me a telescope, so I was able to explore it [space] from the comfort of my home.

Eventually, I decided that I wanted to major in astronomy and physics. I went to Wesleyan University for my undergraduate degree, and I was introduced to Dr Martha Gilmore, who is in the earth and environmental science department. She’s a planetary geologist, who primarily focuses on Venus and Mars, and also, she is a black woman. I’d never met a black woman who studied this stuff. And it was just amazing. So, she became, and still is, my mentor – you don’t really retire out of that.

She taught me a lot about Martian spectroscopy and remote sensing, and she allowed me to do research with her looking at minerals on Mars.

WHY DOES REPRESENTATION MATTER?

I grew up partly in Louisiana and in Houston, and I did have black mentors growing up, I had teachers that were black. But with regards to learning about space exploration, all I saw were white men.

I don’t think I was even exposed to Mae Jemison [the first black woman to travel into space], which is kind of sad. I only knew about her once I went to college.

It’s not that I didn’t think that I would see a black woman in my field. I was just excited to see one in my field because it gave me the message that if she can do it, I can do it. And it was definitely one of the factors that kept me in the field. Of course, it was also the love of mineralogy and spectroscopy that kept me here.

This is actually one reason why representation is so important in STEM, especially for little black boys, little black girls or any other child that’s an underrepresented minority. When they get into a field that’s been run predominantly by white men, they want to see someone that looks like them.

Of course, the field is going to be very difficult, race aside, because this is a complex topic. But seeing someone there who looks like you, and they went through the fire, came on your side, and they’re well-respected and well-known in their field – it gives you hope.