Astrobiologist/Geobiologist uses Earth as a lab to examine possibility of extraterrestrial life

A plaque on the door to one of Perl's chemistry labs. Photo by Howard Frank. Courtesy of JPL

A plaque on the door to one of Perl's chemistry labs. Photo by Howard Frank. Courtesy of JPL

Our species has always been characterized as adventurers. Individuals move boundaries to find new worlds and discoveries. Navigators, seamen, geologists, and mountain climbers break barriers.

The Jet Propulsion Lab’s Scott Perl, Ph.D. is an explorer. He’s a modern-day Indiana Jones, trading in the old leather hat and whip for a white lab coat, latex gloves, and the combined skillsets of planetary geology and microbiology.

His job is to answer the question, could there be life on other celestial bodies in our solar system?

And as the late astrobiologist, Carl Sagan said, “We can't help it. Life looks for life.”

So why explore the possibility of life beyond Earth?

“We are scientists that are exploring the possibilities of life elsewhere outside of Earth, the preservation of what would be signs of ancient or extinct life, and the conditions needed and presence of potential present or extant life.

The presence of current or extant life in terrestrial systems on Earth that we use to emulate planetary bodies allows us to see how biology evolved and adapted to our own ecosystems. Typically, our research looks at closed-basin lake systems, subglacial lakes and oceans, and hypersaline brine sites. We’re utilizing these environments on Earth to help us determine how biology would be preserved and thrive in the subsurface of Mars and below ice sheets on Enceladus and Europa.”

The mission of the Jet Propulsion Lab (JPL), funded by NASA, is to explore the solar system’s planetary science and astrobiology. Set on 168 acres in the foothills of the San Gabriel Mountains near Pasadena, California, it’s run by the nearby California Institute of Technology (Caltech).

JPL’s serene college campus-like settings belie the scientific work done at the facility. On display in a courtyard is a full-scale Perseverance rover, the very same vehicle that’s now probing Jezero Crater on the Martian surface. Other noteworthy rovers, satellites, probes, and of course, rockets have been engineered on this pristine campus. Scott was the investigation scientist on one of these orbiters, the Mars Reconnaissance Orbiter (MRO) for nearly 7 years utilizing CRISM, an orbital spectrometer on MRO’s science payload. He compared these orbital datasets of hydrated minerals to the salts that he uncovers during fieldwork around North America, the United Kingdom, and South Africa. 

Scott Perl, Ph.D., of NASA’s Jet Propulsion Lab

Scott Perl, Ph.D., of NASA’s Jet Propulsion Lab in front of his fully equipped and customized geobiology HORIBA LabRAM HR Evolution Raman Microscope with AFM. Photo by Howard Frank. Courtesy of JPL.

Perl’s credentials are impressive. He’s a research scientist in geobiology & astrobiology, the co-principal investigator for the JPL Origins and Habitability Lab, a visiting professor with Caltech’s Geological and Planetary Sciences (GPS) department, and a research affiliate at the Los Angeles Natural History Museum.

Perl’s path was defined long before now. He was the first student collaborator on the Mars Exploration Rover (MER) Mission as a college student. And that was a purely geological and geochemical mission for the time. This mission was pivotal in understanding the duration and timing of ancient groundwater in the Burns Formation on Mars.

Geobiologist and astrobiologist sets goals

His geobiological and astrobiological research aims to understand how life can thrive in extreme environments. The biology that can thrive in these environments tends to be tolerant to high salts. These halophiles leave behind evidence of its former or current habitats, whether it’s waste from its metabolism or artifacts from the microorganisms itself.

It’s important to remind ourselves at this point that we are not looking for any complex life.

Instead, he seeks microbial life, organisms that flourish on Earth’s most hostile environments.

He uses field sites on Earth as his planetary test beds and looks to investigate the persistence of life as we know it here to geological and potentially biological signs of life elsewhere in the solar system.

It’s a straightforward process. By understanding life in extreme environments on our own planet, we can better understand how life on Earth endures within these extreme environments. This in turn can help us understand how life, its chemical biomarkers, and physical biosignatures in the mineral record can be preserved and confirmed on other solar system bodies. Perl led a 2021 Astrobiology  manuscript that details how to decipher between physical features of biology in the salt record and their chemical byproducts.

To understand biomass and biosignature/biomarker preservation, sample collection is necessary from the field of Earth’s extreme environments and real-time analysis is critical. Porting these over to what a future astrobiology mission would require are critical for understanding how to extract the science from eventual planetary data. 

Extraplanetary aspirations

So, why is it important to study the possible existence of life on other bodies in the solar system?

“I think at the very nature, when it comes down to exploration, it’s a human initiative,” he said. “We can go into the history of our own planet in terms of how we explored with “new” continents and lands and what those drivers were.”

“But on a much more modern and fundamental level, it’s the ability for us to find environments. It’s what we think our place in terms of where we are in our universe, humanity as a species in general, our planet, and all the species that live on our planet. When you think about the arrangement, the biodiversity of all of the species on our own globe, being able to understand other worlds, other kinds of evolution in this case are a mystery. Right now, we only have one datapoint throughout the history of life on Earth.”

Life on this planet evolved and then diverged into what we classify as our trees of life. Our whole animal species in this case is one part of that. And then how we evolved is another part prior to that. All cellular life and life in general came from a central point. The evolution of our own planet was in-parallel with the beginnings of life. 

“When we look at other environments in our solar system, the comparison to Earth, for example, in terms of where we have certain environments that are habitable, we’re trying to understand how life could have evolved elsewhere with different geochemical and geobiological parameters. Basically, how is life adapting and thriving in these environments? And so you have a series of microbiological and geochemical properties that could can get transposed onto other worlds, and sometimes can't. And if you can't, it could be for reasons, in terms of evolution, in terms of different temperatures, different salinities, and different mineral kinetic environments.”

We know biology to be very robust. If given enough time and energy and nutrients, from sunlight or chemistry, and when they can adapt to an ever-changing environment, these adaptations would reflect the local and global environment in a planet’s history.

So, the concept of life detection as we do it now is in the ancient biosignature realm, where we're not looking for present life on any of these worlds. We're looking for preserved signs of ancient life. This leads to our questions about robust biosignatures that could survive over geologic time. For the areas in icy world oceans and the subsurface of Mars, the environments could be more hospitable for cellular life. These are the future targets of astrobiology missions.

The search for life

The paradox is that when life evolved on Earth, in terms of after LUCA, (the Last Universal Common Ancestor, the last cellular species that had commonality between the starting of the actual tree of life), our LUCA is something that all the actual species and all trees of life can go back to.

That was the last thing that was common between everything on Earth. So, if you were to assume that the tree of life for Mars is completely independent of that of Earth, and then the tree of life for Europa and Enceladus, the moons of Jupiter and Saturn, respectively, have the potential for life, but we don’t have any evidence that life exists from our experiments on Earth.

These are icy moons and bodies. When it comes down to icy moons in the outer Solar system, typically there's an ice shell that has liquid water underneath, and the volumes of water can differ.

The pressures can differ greatly in terms of Europa versus Enceladus, for example.

Orbital data from Viking and subsequent orbiter and in-situ studies showed that water once existed on Mars. That meant that there was once water on Mars, which translated to the assumption that these environments were once habitable for life.

But that’s not proof of life.

The jump from water to the jump to organics, to the jump to life detection, means if you have biology, you have all of those other things. But if you have water, it doesn't mean you have to have organics. If you have organics, it doesn't mean you have to have biology.

Here’s where it comes together.

“If you have biology, you have ordered sets of organics in cellular compartments. You have cells that are microbial life. So, if you had, let's say, a radiation tolerance species on the surface of Mars that can live in very low water activities and utilize photosynthesis in that very hostile environment, life would propagate in areas where it can get nutrients where you're not pushing the bounds of ionic or temperature constraints. There are certain ranges in that cells just can't perform any functions. And so, if you're within these ranges, and everything is fine in terms of your actual climate, as well as energy and other things . . .”

You have the possibility of life.

“If you're in this realm or in this range or set of ranges, life as we know it, could exist, right?,” he asks rhetorically. “If it's already there, and was untouched from contamination, we would need to completely ignore Earth’s origins of life here. It would be a separate and independent evolution

While all the work obviously assumes life had started at some point, Perl doesn't do any origins of life research, but colleagues in his Origins and Habitability Lab group do. This provides an intellectual basis for merging the two disciplines.

Based on our technological advances, or lack thereof, if we’re going to look for signs of biology on this planet, it's easy, especially with Raman, to look for organic hotspots in areas where you know you might not be able to visualize and see the cells that you're looking at. But you'd look at certain organics.

“If I took my Raman spectrometer, and I was able to see where the cells were, I would get spectra that vibrate at what those organics are vibrating at,” he said. “It's not necessarily going to show me the cells, though. There's a trend between it vibrating everything spatially, but to ensure confidence in the cellular compartments, I need to back up my geochemical and geobiological spectra with spatial images that are at the resolutions of very low biomass systems.

“If the cells were lysed (sliced) or long gone in this case, you can imagine that the cellular compartment can basically spill everything out onto a rock or onto a mineral. The Raman vibrations are still going to pick all that up. We can still see what was there, but a slab of organics that are basically the blood, sweat, and tears of what was in the cell isn't alive.”

On Earth, if you're looking at ancient environments, it's actually difficult to find areas where it's devoid of life.

“So, one of the things that we do, there's modern contamination in this case or modern kind of microorganisms in older environments, and we know that we're trying to separate out what is younger versus what is older.”

He uses isotopic evidence to understand what features the kind of precursors were of the older material. Typically, the way isotopes can be robust over geologic time gives you a certain biotic or biological range of what was left over from those original cells.

“We are in part looking at the waste products of these cells. Waste, blood, sweat, and tears. These are the waste products in terms of microbial growth.”

These are the products in terms of respiration, metabolisms, and cellular growth. In low-nutrient environments where you have microbial competition for nutrients, if the nutrient supply is not bioavailable or inaccessible from the cells that are there, cells can cannibalize one another.

That really depends on that strength in numbers, from a microscopic point of view. But it's evidence of life. “Any bulk measurement needs to be backup my spatial proof, and vice-versa. That’s how we would convince our science communities. The resolution of evidence needs to be in line with what are actually measuring.”

Mars Evidence?

Evolutionary chart of life for the Earth and Mars.

Evolutionary chart of life for the Earth and Mars. Photo by Howard Frank. Courtesy of the JPL.

The Von Karman museum at JPL is stocked with examples of rovers and satellites that have explored the Red Planet. And for every single Mars mission, including Mars 2020, we are in the red, pointing to an evolutionary chart of life existing and not existing. The current Mars portion is in the red, meaning that we are seeking signs of ancient life”

“These missions are not looking for signs of active life or extant life with the current missions, by design. We're looking for signs of extinct and ancient life,” Perl said. “Now, even that word, ancient life on Earth, makes total sense because there were species that were alive on this planet that are no longer alive. We see evidence of that. You don't have to justify that life was present on this planet 2.5 billion years ago and older. Our laboratory has the capability to quantify present/active/extant biology as well as signs of ancient life in the form of biosignatures”

Now we just make the measurements to match what we're actually observing. Going back to that diagram, the green and the red, we don't know what the green section is for Mars yet. We can only go by what we have in, in the products that are left over from life.

We see evidence that organisms changed our atmosphere. Having an ancient life paradigm for planetary systems in our solar system, we have no evidence for any life at all. We're at this strange impasse where we can take the features that we know for life as we know it, and build instruments around what we think life utilizes, what life is, and what the framework for life is.

Perl studies pigments in cells. The reason why the cells are making these pigments is to adapt to a change in solar flux. It's an internal sunscreen bottle that's shooting out certain keratinoid pigments over different doubling times. And as cells evolve and as different cellular communities evolve, that adaptation process is something that the final or current cell regime. His two recent papers discuss modern carotenoid pigments and their preservation alongside the UV-C robustness of beta-carotene in Martian analog settings.

“If I'm going to go to an area like the Great Salt Lake, for example, the entire North arm of the Great Salt Lake is pink. That's because of adaptive microbial pigments. If this is put on Earth, [as he points to the figure] we're always going be in the green (active life), unless you're in certain areas like Don Juan Pond in Antarctica during some times of the year.” Perl and co-authors wrote the first astrobiology chapter in the first Great Salt Lake biology textbook, kicking off several lines of work from a modern planetary analog.

Some areas on Earth are too hot for life. In some areas, the pressures might be too great. There’s Marianna's Trench (the deepest oceanic trench on Earth), for example. There are red hotspots of non-habitability on our planet, but for the most part, we're always going to be in the green because of the cellular diversity on our planet, including plants, and animals.

But we don't have a framework for life as we don't know it until we get a second data point for life. We have Earth’s evolution, and this worked to an extent. That’s where the organic jump comes in. Survivability of select organics on the surface of Mars made sense because you had water, and because you had water in these systems you had life.

And that life would have propagated using those fluids and flourished on Mars. But that’s in theory. We need to go deeper into the Martian subsurface.  

“We have absolutely no evidence of that,” Perl stated as the current status of scientific findings.

Of course, the Mars 2020 Perseverance rover with its host of Raman, XRF, and other research instruments may change all that, and quickly, but for now, this is where we are.

Yet it’s likely that underneath all the Martian dust scanned by the spectrometer on the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) from the Mars Reconnaissance Orbiter over a period of 15 years leads Perl to conclude that, it's likely that underneath all of this dust, there are more of these minerals, fluvial transformations, or kinds of fluvial interactions.We are just not seeing these materials because the dust is getting in the way of the spectrometer. That instrument just ran out of energy and shut down in the Spring of 2023.

And the mineral data indicate where water once existed by the types of artifacts it left behind.

Being able to distinguish between these actual different chemistries here is critical because there is a kinetic relationship between water activity, and what makes clay, what makes a salt mineral. That includes sodium chloride, magnesium chloride, and potassium chloride.

“The change in that mineral kinetics not only dictates your final mineral source or what gets precipitated. That's your last known chemistry of the water that was once there.”

It tells you where 3.5-billion-year-old (GYR) water touched some rock or made or precipitated some mineral.

Geobiologist and astrobiologist’s motivations

So, why does Perl dedicate his life to the study of the chance of extraterrestrial life in the solar system?

When he was at Stony Brook as an undergrad, a university on Long Island, N.Y., he had the same types of curiosities. He wondered about life in extreme environments, water on Mars, and things that come back to his overall curiosity about the evolution of life on our planet. It’s something that’s a completely isolated event from the rest of the solar system. As a doctoral student at the University of Southern California is where, while a full-time research scientist at JPL, he planted his flag in geomicrobiology.

Mars had standing bodies of water, fluvial water moving through the groundwater table, and paleolakes, lakes that existed in the past and were present throughout the Burns formation. The Burns formation is a Mars region characterized by a layer of sandstone embedded with spherules (small spheres) of hematite, a common iron oxide compound, and referred to as blueberries.

“You can tell how much water flowed through the system based on the lack of soluble minerals and also what's called secondary porosity. We don't see the water at all. We just see the evidence of the minerals left behind.”

But Perl didn’t know if he had the skill set to determine if the conditions on Mars were favorable to an environment where life could adapt and thrive. So, he went from a bachelor's in geology and material sciences and did a Ph.D. in geomicrobiology, geobiology and geological sciences, to really examining life in extreme environments.


The Great Salt Lake

HORIBA LabRAM HR Evolution Raman Microscope with AFM.

HORIBA LabRAM HR Evolution Raman Microscope with AFM. Photo by Howard Frank. Courtesy of JPL.

And so, he took what he learned from a purely geological point of view and with those original questions, moved that over to life in extreme environments and to salt minerals and to hypersaline brine.

He studied the Great Salt Lake, as a kind of geomicrobiological field site after moving from just Earth science and planetary science to more geobiology. When he studied the groundwater history on Mars, he was looking at the loss of soluble salt minerals due to ancient fluid interaction. Now he was looking at the precursor processes at the Great Salt Lake and other hypersaline closed-basin lake systems where the salt was first forming and then later preserved over geologic time.

Adding geologically old salts to his field site investigations, he has continued collaborations with the University of Edinburgh and the MINAR program (Mine Analog Research) to determine long-term Permian preservation. The salts layered in the lake are 253 million years old and haven’t had any access to the sun during that time. Yet through Raman microscopy, he has shown evidence of abundant microorganisms.

Using the HORIBA LabRAM HR confocal microscope, Perl was able to measure the organics and look inside minerals to look at intact fluids within the cells. All of this has an oxygen-hydrogen stretch. Basically, it's water that Raman can pick up. With the Raman microscope, he’s looking at 253-million-year-old water.

“The Permian salt mine salts is teaming with organics in these fluid inclusions,” he said. The same exists for the Great Salt Lake minerals but those contain intact and living cells.

Life exists within these minerals that carry fluids.

“When we learned how to use the Raman optics better, we saw the organisms everywhere.”

Microbial Pigments

A large part of Perl’s work involves microbial pigments. One of the questions that arises from life detection is when he doesn't have a data point for what would be on the green part of this evolutionary figure outside of Earth. He’s just starting in terms of what's in the red. Like signs of ancient life, if we have no idea what the source material is, then getting the right side of this is impossible. We're using the Earth’s evolutionary features and life on Earth as a framework right now for life as we don't know it. The framework will fail because it completely ignores evolution.

“If I was a Martian LUCA, or the last common cell or cellular community on Mars during the late Noachian period in the timeframe, I likely needed to evolve to adapt to high radiation, high salinity, and lower water activities. Life needed to go from living in high-water activities to lower-water activities. All life on Earth is between 0.58 and 0.99 in salinity. Any ocean is going to be the higher of that range. But life would need to adapt. So Deinococcus radiodurans, for example, is a radiation-tolerant microbe and can live in harsh Earth desert environments at low water activities. And so, the features of life as we don't know it is somewhat hindered because we don't have an evolution on Mars.”

When we look for life outside of Earth, we need to consider its ecology. How is it thriving in some environments? We have planetary analog systems on Earth that have this chemistry right now, like in terms of the Great Salt Lake. The fluids that are found in terms of the Great Salt Lake, for example, would be the same salinities that we would've likely had on Mars.

And a Martian microbe would have had to be halophilic (an organism that thrives in high salinity environments) because Mars’ closed basin and lake systems tend to be a lot higher in salt.

It's not getting any new water. It’s going to get saltier and saltier as time goes on. Perl looks for microbial pigments because they can be a universal adaptation process for any kind of microbial life.

For radiation. Or photosynthesis. Or chemotaxis.

Raman spectroscopy enters the study

The pink-pigmented parts of the Great Salt Lake samples are from beta carotene – the same pigment that’s in carrots. Except this is produced by these halophilic organisms. Three peaks appear in the Raman plot.

“It shows that these are the pigments trapped in the fluid. So obviously Raman is measuring the fluid, it's measuring all the carotenoids. It's able to give me an idea of everything that is organic, everything that is elemental, and everything that is biological in the system.”

The yield of the chemistry corresponds to what can survive over geologic time. The pigments in the very modern case are extremely robust.

“If you lyse this up and you throw that into Raman, it's still Raman active. You're not changing anything,” he said.

But like, think of marbles in a jar, marbles in a tin jar. If you had three of them that were big and you shook it around, you'd get a sound and you could tell that there were three or a small number. If you took those three marbles and you bashed them to some larger amount than three and put it back in the same tin, can, it's a lot more, but they're vibrating in a smaller intensity. Same thing, the same kind of vibration that just then scattered about.

A full-scale model of the Perseverance rover, currently operating on the surface of Mars.

A full-scale model of the Perseverance rover, currently operating on the surface of Mars. Photo by Howard Frank. Courtesy of the JPL.

The bottom line

Perl is looking for an agnostic sign of life that is robust over geological time.

“Going, going back to the different evolutions, I personally would never design any life detection mission to look for DNA. DNA is, is an Earth product. That's our own evolution. We had RNA before that and we learned 50 years ago, when we thought that protein was the vehicle from which generations learned, from the last generation cells to adapt. That's just 50 years ago, not a long time.”

A genetic code is passed on. We already know what DNA looks like on Earth. It's not the DNA that we should be searching for outside of Earth, Perl says. The properties of life show that the parent generation passes on all of those adaptations and all of that code to a younger generation. It doesn't need DNA as we know it to do that. It might be another nucleic acid that is doing that job that is DNA-like, or RNA-like, or protein-like.

“But this kind of goes back to what I was saying at the beginning. How far back in Earth's evolution and tree of life do we go for a universal agnostic biosignature? Are proteins universal for life? Is it the complex proteins that only life would evolve to have this?”

Perl notes if he is looking for what complexity is to you, what is complexity like? Obviously again, water, organics, biology, all biology has complexity in it. But if you can form those complex organic structures, not from biology, and you don't have the initial biology to give you your positive control searching just for that, you have a gap.

“And that's what I'm trying to fill in here. What is the gap between the planetary geology kind of exploration and the microbiology needs to validate life outside of Earth?”

These may be from life if we were to find a sign of life, and we were to find cells moving in any brine system outside of Earth. It would be going through non-Brownie motion that looks like the features on his Raman video (movement of microorganisms on a Raman microscope), the very next question is going to be, well, what is it?

He’s trying to understand agnostically, what would make sense for a non-terrestrial evolution, a non-terrestrial ecology using the lessons that Raman really teaches him in terms of preservation of cells, how organics can degrade or not over geologic time, and trying to piecemeal that water to organic, to biology route. But he’s doing it from what he can tell on the preservation on Earth to what would bode well for extant life.

That’s life that's present right now. And in other solar system bodies, the Martian, subsurface, Europa and Enceladus.

“It’s my main, non-Earth study sites,” he said of those bodies.

But this whole thing comes down to curiosity,” Perl said. “It doesn't come down to developing better medicines or feeding more people or any of the social reasons that we all used to question the funding of these types of research. It comes down to curiosity. Man's basic nature.”

Challenges in harsh environments

If you had a nutrient-rich environment if the microbes inside the fluid inclusions like at the Great Salt Lake, and a microbe is floating or swimming in that fluid, it’s a nutrient-rich pool. If it’s swimming in its food, it doesn’t need to swim. It only has to open its mouth, metaphorically. In a permeable cell form, those ions are making their way through the cell wall. And it’s getting its lunch. If it’s already getting fed, it doesn’t have to do anything. It’s, I'm going to go through cell division and go through this process and life will flourish.

But in these harsh places, we are talking about nutrient-poor environments.

“I have to seek out where the leftover lunch tray is. It depends on the quality of the food needing to seek out what's there for its nutrients. Life can evolve. The ability to have a motor to swim inside these nutrient-limited systems is important. The, need for nutrients is just as important as the need for those nutrients to be bioavailable. So, this is why we look for solvents.”

In any kind of solvent. Taking pieces of the periodic table. We dissolve a sodium chloride mineral; we dissolve a salt crystal inside non-saline water. The salt crystal disappears. But the chemistry of that crystal is now in solution. We’ve raised the salinity of that solution by a fraction of an amount.

We keep adding salt crystals to that non-saline solution. Eventually, it's going to become saline. The chemistry of that, of not just the process before the salt is added, but the chemistry of that change over time is critical. And then the eventual brine that exists is where you can't dissolve anything more.

You've completely saturated the solution. So when you're in a mineral state, you're in this fixed-ordered pair of ions independent of water. Life utilizes minerals to thrive. It’s parts of those ordered pairs of those minerals. And if it's in solution, removed the crystalline jacket that it was wearing and now it's in solution and now you're able to consume it.


Perl’s labs include anaerobic chambers of cell incubators, cryochambers, DNA extraction, and protein extraction. The oxygen extraction is to mimic prebiotic life.

But at the heart of one of his labs is a HORIBA LabRAM HR Evolution confocal microscope with AFM and other attachments. It’s where he does his nanoscale observations. He and his team call this large instrument GARAK, after the Star Trek character. A sticker on the side of the instrument features GARAK’s headshot and explanation of it as an acronym, a practice sentimentally shared by many scientists that become attached to their equipment.

GARAK, the Star Trek character, is a Cardassian, a warrior species and natural enemy of the human race. But GARAK is a wise man, knowing things he keeps quiet about until the situation dictates his wisdom. GARAK stands for Geobiological & Astrological Raman for Atomic Knowledge in the lab.

Perl and his team chose the LabRAM (Now the LabRAM Odyssey) because he wanted an instrument that he wouldn’t have to upgrade for a decade. It’s equipped with atomic force spectroscopy , and with its tips in tip-enhanced Raman scattering mode can focus light on nanometer areas.

“I want to be able to do all of these analyses, and I want to be able to have the resolutions and wavelengths and gradings and all the things that I don't know about yet to make these observations happen, Perl said.

“Part of it was the pigment work that we talked about earlier. Part of it was cryo work, where essentially frozen brine is in solution. You have cells that can thrive in frozen environments, so we can be able to make measurements in ice. What you're seeing here is actually one of the slowest cryogenic experiments. All of the white moving features are microorganisms. These are halophilic microorganisms that are also cold-tolerant. They are fine in the cold. You can freeze them down to minus 180 degrees and colder.”

Understanding how these microorganisms flourish might help Perl understand how organisms on icy planets propagate.

“Now we can make Raman measurements in ice.”

Perl said if he assumes that the evolution of life on or in the Martian subsurface and in the ocean world that is something did exist, what are the microbial byproducts of that existence in this case? Pigments are big in terms of evolution that can help shield you from UVC/solar radiation, byproducts of what's modified in terms of the ice byproducts that like track fluids for hundreds of millions of not billions of years. If he were to trap a fluid and had that be contained for three and a half billion years, that's a paleoclimate record. That fluid is three and a half billion years old, or 255 million years old.

“It's amazing,” he said. “And it's the same environment. That would be the last ancient water that was on Mars preserved.”

And thus the analog to the Great Salt Lake here on Earth.

A sticker on the side of JPL's LabRAM HR Evolution Confocal Raman Microscope identifies its nickname as GARAK.

A sticker on the side of JPL's LabRAM HR Evolution Confocal Raman Microscope identifies its nickname as GARAK. Photo by Howard Frank. Courtesy of the JPL.

The future

Fifty years ago, researchers were doing flybys and long-range orbiter missions. The main focus was robotics. Mars 2020 is a robotic space flight. But what are the needs of future humans when they do get to places like Mars and to the ocean world, more so Mars in our lifetime, using robotics as a tool set for humans?

And that’s what Mars 2020 and the Perseverance rover is doing, drilling, scanning, and taking samples for future flights to return to Earth for further investigation.

”Humans are always going to need instruments and tools to get to the subsurface. You can send humans to Mars right now, and they're going to be stuck at the surface, just like all of our rovers. Their scientific capacity for certain experiments will be limited by what we can give them to work with in the future. And being able to establish a permanent science laboratory potentially on Mars or having long-term investments and being able to extract samples from the deep sub-surface is critical for determining the evolution of potential life on the planet.

Perl is the science lead for a Mars subsurface extraction, project. And he expects to be able to get down to a hundred meters in depth.

What is the scientific rationale as we go deeper?

“What do we expect to find from certain kinds of lain sediments (secondary rocks often the result of the accumulation of small pieces broken off pre-existing rocks that were formed from ancient waters). You have your highest and best quality preservation metrics at play in terms of the Martian subsurface. So being able to not only extract what's there, but not contaminate it with what you're extracting it with, and making the Raman measurements, where you're getting the organics, the minerals, the elemental chemistry, and then potentially the actual biology. But your instruments can’t contaminate the samples. But the interpretations of what you're looking for, you can say with a hundred percent confidence that it is Authigenic [CQ] something that is from the environment that you are examining.”

Perl used a contemporary analogy to describe his work.

“You can kind of think of it like you're playing a CSI detective.”

“The clues that are at the scene are from the scene. If you were to take those clues and transport them elsewhere or bring in something from the outside environment in, it's not going make sense for what you're trying to examine. And so doing this in place is hard along with doing this in time when those clues have degraded over geological time.”

We know how much of something can be lost before the thing is no longer identifiable. That question is the same thing that we would pose for any dead cells, for any extinct life. In terms of the carotenoid bonds, those actual pigment bonds, even when they're lysed, it can give you a vibrational mode that we can measure.

Again, the power of Raman is on display to investigate life possibilities outside our home on Earth.

We assume that life on Mars is not going to look exactly like life does on Earth. But there will be similarities.

“It'll, it'll have a lot of the properties with regard to evolution,” Perl said. “It should be able to divide in terms of going through cell division. It should be able to adapt to its environment. That's why pigments are such a huge deal for me, because in those adaptation processes, you get a chemical biomarker, and you get the chemistry of what that is. You can verify that it is indeed a pigment. All pigments are colors, not all colors are pigments.”

Regardless of Perl’s dream to send a manned mission to Mars to sample the depths of the Martian subsurface, it’s clear that his drive, and that of his peers, will be bolstered by their natural curiosity, hunger for answers, and new discoveries.

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