Mars life signs probed by spectroscopy

Andrew Czaja stood frozen in his family room on the afternoon of February 18, 2021. Surrounding him was his wife and two kids, watching the NASA broadcast of the Mars 2020 Perseverance landing.

Czaja wasn’t a typical observer. The University of Cincinnati associate professor in the Department of Geology specializes in Precambrian Paleobiology, Astrobiology, and Biogeochemistry. His focus is on the origin and evolution of the earliest life on Earth.

But Czaja, Ph.D., is also a member of the Mars 2020 science team. His job is to help choose which rocks will be collected for future retrieval, returned to Earth and subjected to extensive study.

The atmosphere in the family room was tense. The planned touchdown of the Perseverance rover with its array of scientific instruments was scheduled for 3:44 p.m. EST. Yet because it takes radio signals about 11 minutes, 22 seconds to travel between Earth and Mars, the wait was excruciating.

“I started thinking about everything that had to go right for it to land,” he said. “And it really started making me nervous.”

Czaja couldn’t sit, choosing unconsciously to stand still nervously watching and listening for the touchdown confirmation.

At 3:55 p.m. EST the announcement was made. Perseverance landed on the surface of Mars.

That’s when the real excitement began.

During its first couple of months after touching down at its landing site in the delta area of what’s thought to be an ancient lake called the Jezero crater, Perseverance is checking out its systems slowly to make sure it’s all functional. It’s moving its arm equipped with imaging devices and spectrometers, turning on instruments to make sure it’s all working properly, and collecting data from nearby rocks to determine if it’s sending data back.

Those instruments include the Planetary Instrument for X-ray Lithochemistry (PIXL), an X-ray fluorescence (XRF) spectrometer with a high-resolution camera to determine the fine scale elemental composition of Martian surface materials. PIXL will allow more detailed detection and analysis of chemical elements than ever before. It’s mounted on the Perseverance’s robotic arm.

The rover also includes a UV Raman spectrometer ― known as SHERLOC, which stands for Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals. SHERLOC uses cameras, spectrometers and a laser to search for organics and minerals that have been altered by watery environments and may be signs of past microbial life, according to NASA.

The Raman spectrometer can also do UV-VIS and NIR spectroscopy. It's the instrument that’s produced most of the data thus far, and referred to as the SuperCam instrument.

The imaging data has indicated several things already.

“There’s a very interesting variety of rocks,” he said. “From orbit, we could see that there's this area, which looks different from this area over here. So we've called them different types of rocks. But it's a little hard to tell for sure which rock is older. Now we're on the ground, we can start to really see more details of it.”

Some are rounded, while others are flat, looking weathered and eroded.

“It's just an interesting mix of rocks,” he said. “And we don't understand yet where they all came from or how they got there, or if they are where they've formed initially. And they've just weathered out in strange ways. So, we haven't learned a whole lot yet, but we know more than we did, and now we know which specific questions to ask to continue to learn about this site.”

The mission is beginning to collect some spectra, or chemical information about the rocks. Czaja and the team can now start to hypothesize about what these rocks are and how they formed. They don’t know if the bottom of the crater floor where the Perseverance landed is a sedimentary rock formed by materials flowing into the crater from outside, or if it's igneous rock that was formed by a lava flow that came in and filled the crater.

“We couldn't tell that from orbit,” he said. “But that's the question we have and that has big implications for the history of the crater, what types of rocks we're going to be studying and what questions we can ask about them. So that's kind of a first order question. What kind of rock is it?”

Surprisingly, the scientists can do spectrographic measurements from about 7 meters away with the SuperCam, so the Perseverance doesn’t have to drive up and put the spectrometer down onto the rocks. But the SHERLOC and PIXL instruments must be in contact with a rock.

Czaja said there's also potentially some carbonates that were deposited on the margin of the lake. On Earth when you get carbonates deposited on the margin of a lake, it's often associated with life. The team wants to collect samples from the delta, which he said has some “really awesome fine grain deposits,” since that’s a great place to look for organic carbon.

There’s a chance the rover could go beyond the crater and explore its edges, where scientists can learn more about the planet’s evolution.

Czaja is a return sample scientist for the mission, helping to make decisions about what rocks to sample to bring back on a future return mission. Right now, that’s estimated to be about 10 years out. He’ll be involved in data interpretation of the PIXL X-ray spectrometer instrument and the SHERLOC UV Raman spectrometer, which also does fluorescence measurements.

“Raman imaging and fluorescence imaging, and also spectra, of course, those are the things that are going to give us the most in situ close-up magnified detail of the rocks,” he said.

Back in his lab, Czaja uses a HORIBA T64000 Triple Advanced Research Raman spectrometer system to find trace evidence of microscopic bacteria, like mineral-filled fossil remains or chemical carbon signatures that indicate life left behind by the bacteria’s cell wall.

He can put a thin section with the fossil under the microscope attached to the Raman spectroscope and focus the laser on it. It gives him a spectrum of whatever material it is. If it’s made of organic carbon, he has one more piece of evidence proving it was once alive.

When the Mars rock samples finally arrive back on Earth, Czaja plans to use his Raman spectrometer to perform the same types of analyses he does with terrestrial samples to see if he can build a case for life existing in the ancient rocks.

Back on Mars, Czaja will be trying to determine what kind of rocks Perseverance is looking at and whether there’s a chance of a bio-signature in the rock, an organic carbon in there. He’ll also examine the textures of the rock to determine whether the features were made by microbes or a microbial material.

And that will help determine whether or not life once existed on Mars.

Choosing the rocks will be difficult. There are a limited number of sample tubes, and you can’t dump a sample that’s been collected and put in a new one.  So choosing a sample is a long-term, one-time commitment.

Since the return of the samples could be more than a decade out, Czaja isn’t sure he’ll still be doing research. But if not, he hopes his students will be the ones who look at it.

The Mars 2020 mission will also try to understand the planet’s climate history, because if life got started on the surface billions of years ago, it must have been vastly different than it is now. And there's lots of evidence that it was. There was water flowing on the surface, with ponds and lakes. But we only know that from surface and its geomorphological (physical surface features) evidence. We can see river channels and lake deposits. Therefore, there had to have been lakes and rivers at some point, but when that occurred and how long it was around are mysteries Czaja hopes to solve during this mission.

“If we learn about how climates can change on another planet, it can help us understand climate change more generally, and how Earth's climate changes through time,” he said.

Finding life existed on Mars could prove significant.

“If we find evidence that life originated and evolved on Mars, that would be a big fundamental shift in our knowledge of life,” he said. “That and the fact that life was able to get started on a second planet, which of course, it similar to the nearby Earth in the same solar system. But it's a different planet. And that would help us know that life could get started relatively easily, that it didn't require some special circumstances that only occurred on our planet for some reason. It gives us hope that we could find life on planets, others around stars more easily, because that means it's easier. That life is maybe not inevitable, but for life, it doesn't take special circumstances.”

But Czaja said if we find life on Mars once existed, yet was nothing like that which we find on Earth, it is not only a possibility, but poses a problem. It goes towards how we look for life on other heavenly bodies.

“If it's nothing like life on Earth, we may miss it because we're not looking for it,” he said. “We know how to detect life here on Earth. It's not that hard, even though we can't define life very specifically by saying it has these properties. Fire has a lot of the properties of life. It consumes fuel and releases energy and changes its environment. It grows and develops, but we wouldn't call it alive. You sort of know life when you see it, because all life on Earth has a common ancestor as far as we can tell, and uses the same biochemistry.”

Carbon happens to be an ideal molecule as a basis for life.

“It's not like carbon was by chance what life used here on Earth. It has a lot of properties that makes it very useful for life that most other elements don't have. And so it's very likely that life would use carbon. It's also a very common element. So we look for carbon, look for organic carbon, meaning carbonaceous material like biology has made out of here on Earth. We're not just guessing that it’s all of what all life would use. There's a better than good chance that carbon is what life would use. But it’s not a guarantee.”

Yet if we were to detect life based on some other form of chemistry, it would be exciting too, since it would broaden our already far-reaching definition of what life could be. It can give us more hope that if life doesn't even require the same elements, then maybe life is abundant in the universe, and we just don't know how to detect it.

Yet.

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