Astrum Space - All the Evidence We Have For Life on Mars

Episode Date: January 29, 2026

A compilation of ‪Astrum’s best content about the search for extraterrestrial life on Mars. What biosignatures are scientists hunting for? Where could life be hiding? And what did NASA's Perseverance rover discover on the leopard-spotted rocks?▀▀▀▀▀▀Astrum's newsletter has launched! Want to know what's happening in space? Sign up here: ⁠https://astrumspace.kit.com⁠A huge thanks to our Patreons who help make these videos possible. Sign-up here: ⁠https://bit.ly/4aiJZNF

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on April 30th, the powerful vocals of Demi Lovato on May 17th, and the signature Southern Country Rock of Eric Church on July 19th. Tickets on sale now at Yamava Theater.com, only at Yamava Resort and Casino, celebrating its 40th anniversary. You in? Must be 21 to enter. You've likely all seen the news by now. NASA found a possible sign of life on Mars. These tiny spots, barely visible to the naked eye, are the biggest space news in over 50 years. If this really is a sign of life,

it would be the most meaningful discovery in the history of humanity. But we've been burned by false alarms before. So have we really done it this time? I'm Alex McColgan and you're watching Astrum. Join me today as we dig into the details of what perseverance found, why scientists are excited and what it will take to prove we're not alone in the universe.

In February of 2021, NASA's Perseverance rover, or Percy to his friends, touched down on an ancient Martian lake bed. The Yezaro crater was once home to a large body of water, with rivers flowing in and out, carving deltas and carrying sediment. The soil is rich in clay minerals that can only form. in the presence of water. Percy has been sent to hunt for ancient microbial life. If it's going to find them anywhere, the Yesero crater seems like a good bed.

You see, ancient lakes often contain perchlorate, which can be metabolized by microbes. Astrobiologists on Earth study microbes like this in extreme environments to understand if life could survive in similar conditions on other planets. The rover's job is to look for these possible signs of life, identify and store the most interesting samples of Martian rock, and prepare them to be collected by another space mission for an eventual return to Earth. One day, in July 24, while exploring the edges of the ancient Naretva Valis River Channel, Percy's cameras spotted something unusual. A rock from the bright angel formation. Two of the rover's instruments, the planetary instrument for X-ray lithochemistry

or pixel, and the scanning habitable environments with Raman and luminescence for organics and chemicals, or Sherlock for short, detected sedimentary rocks made of clay and silt. On Earth, these materials are excellent preservers of microbial life, so Percy took a closer look. And it It saw something amazing. The rock, also known as Cheyava Falls, was rich in organic compounds like carbon, phosphorus and iron, arranged into rings. Affectionately named leopard spots and poppy seeds, the tiny spots span 200 micrometers to 1 millimeter in diameter, but it was enough to raise the blood pressure of astrobiologists everywhere.

The light inner part of the leopard spot is chemically similar to the surrounding rock, but the dark outer rim is enriched with iron and phosphorus. It seems to be evidence of localized iron reduction. Percy also detected organic, carbon-based compounds in the rock, and based on its texture and geochemical composition, we strongly suspect this rock was once in contact with water. Usually, when we see such a combination of organics, water and iron reduction on Earth is interpreted as a sign of microbial life.

Suddenly, NASA had something very unique on its hands. Could this mudstone rock hold the first alien biosignature ever found? At the center of this story are two very special minerals, Vivianite and Greigite. Vivianite is an iron phosphate. On earth it forms near metal ores and river sediments, where microbes like geobacter metabolize iron instead of oxygen. They take in iron three oxide and release iron two as a waste product. The energy given off by this reaction then powers their metabolism, a process known as

chemosynthesis. When the expelled iron two reacts with the phosphate and the water in the environment, it forms Vivianite. Greyguide follows a similar story. Sulfate reducing microorganisms on earth break down sulfate into sulfide, which reacts with iron to make greyguide. But let's be sceptics for a moment and rule out microbes for now. What else could have caused these reduction reactions? Well, one explanation could be very high temperatures. The sulfide needed to produce Greyguide could have come from volcanic gases leaking into groundwater. But that means the sulfide would have had to migrate from a hot volcanic system into a much cooler environment,

and there's been no evidence for such volcanic or hydrothermal sources nearby. Another possibility is that sulfate in the rocks was reduced to sulfide through reactions with organic matter. But unless temperatures exceed 150 to 200 degrees Celsius, these reactions would be very slow and require a huge amount of energy, making them unlikely. And studies of the rocks around this area have shown no evidence of high temperatures. So there's no way the surrounding environment could have got hot enough to reduce sulfate and form grey-guide. Another possible explanation is acidity.

Both iron-3 ions and sulfate ions dissolve much more readily in water under acidic conditions than they do under neutral conditions, making them much more prone to reduction through purely chemical reactions. If the water on Mars was more acidic than we anticipated, that could have caused the spots Percy saw. Perhaps these spots were just the result of chemical processes on an alien planet. nothing more. But then, Percy spotted this little green mineral. Nestled near the sample site, a small rock of olivine knocked the acidic water hypothesis on its head. Olivine is the fastest

weathering silicate mineral. Unlike other silicone structures like silicon dioxide, for example, oliveine doesn't have strong silicon oxygen-silicon bonds. Instead, it's made up of negatively charged silicut ions held together by the electrostatic attraction with positively charged magnesium and iron ions. In acidic conditions, these are displaced by hydrogen ions, breaking olivine down into orthosolic acid and magnesium ions in solution. The more acidic the environment, the more hydrogen ions there are, and the more aggressive the dissolution of olivine would be. So the very fact that it exists rules out the possibility of acidic conditions causing the strange spots. Science is ultimately about falsification. It's not about proving a hypothesis

true, much more often it's about proving a hypothesis false. Over time and through a process of elimination, all roads seem to point to the same explanation. And if that explanation holds up against enough skepticism, for long enough, it eventually becomes an accepted theory, testable, reliable, and widely accepted by the scientific community. In this paper, the Mars research team tried to prove that these minerals were not left behind by ancient alien life. They started with a null hypothesis and systematically investigated all the non-living explanations for what they found. But after months of study, they concluded they just couldn't do it. Now, saying we can't explain how this was done by something non-living is very different from saying this is a definitive sign of life.

For one thing, all our speculation and contained excitement is based on. on what we know about biochemistry on Earth. And no matter how tempting it may be, we cannot allow ourselves to assume that just because something happens one way on Earth, it would happen the same way on Mars. Maybe it has a totally different biochemistry we know nothing about. NASA's being extra careful not to say too much too soon. After all, we've been wrong about potential biosignatures on Mars before. Back in 1976, the Viking lander tested Martian soil for life by squirting it with nutrients

labeled with radioactive carbon 14. If microbes were present, they'd metabolize the nutrients into radioactive carbon dioxide we could detect, and to everyone's shock, that's exactly what happened. Excited scientists thought they had proof of alien life. But in 2008, NASA's Phoenix lander. found Martian soil to be rich in Placlorate, a powerful oxidant that destroys organics and releases gas when heated. What looked like a biological reason was really just chemistry, a false positive. Still, Mars kept dangling hope. In 1996, a photo of meteorite ALH-8401 made headlines.

The rock itself was over 4 billion years old, from a time of the meteorite ALH-A-L-H-4-001 made headlines. The rock itself was over 4 billion years old from a time when Mars had liquid water on its surface. Under the electron microscope, tiny structures emerged, resembling bacterial colonies. The world stood still. Researchers thought they were onto something big, so big that President Bill Clinton gave a formal announcement about the discovery. Sounds a lot like NASA's recent statement of Percy's discovery, doesn't it? And in 2022, those squiggles were ruled non-biological, explained instead by a water rock reaction

called serpentinization, another false alarm. So is our recent finding in the Yezero Crater another close call? Or is it proof that the third time really is the charm? There's only one way to find out. We have to bring the sample home for further testing. That's where the Mars sample return mission comes in. It's a complex mission, which requires sending three separate spacecraft to Mars. Percy has already completed Phase 1, it's drilled into Cheyava Falls and tucked away a precious

core sample of the Mudstone Rock mission scientist named Sapphire Canyon. Phase 2 would be to send another spacecraft to land near Perseverance, collect those tubes, launch them into orbit around Mars. The third and final craft would collect the samples from the orbiter and ferry them all the way back to Earth. It's a huge task with an estimated price tag of $11 billion. The Mars sample return mission was first announced in 2022 as a joint collaboration between NASA and ESA. Since then it has been fraught with financial struggles and uncertainties, delaying the project from 2030- to 2040, before. for ultimately being suspended indefinitely.

This is despite the National Academy of Sciences Decadal Survey, a meeting of leading scientists who get together every 10 years to decide the future priorities for progress in STEM, naming the Mars sample return as the highest priority for NASA two decades in a row. And that was before we discovered this potential biosignature on our neighboring planet. All we can do is hope this puts political pressure on leaders to mobilize the necessary resources to pull it off. So if we ever do get the Sapphire Canyon sample back home, what kind of experiments might scientists run?

There's a good chance that, among other things, they'll be looking for two key fingerprints of life. The first is chirality. Amino acids come in two mirror image versions, right-handed and left-hand. also known as D and L amino acids. On Earth, life overwhelmingly prefers the L version of things, while non-living materials show more of a 50-50 split. If the Martian sample shows a significant chiral preference, either right or left-handed, that

could be a smoking gun. The second fingerprint is carbon isotopes. comes in a few different flavors, most commonly carbon 12 and carbon 13. Again, life prefers one over the other. The ratio of carbon 12 to carbon 13 in living things is much higher than in non-living things. If we see a similar pattern in the Sapphire Canyon sample, that could be another clue that its origin is biological. You see, you and I may often think of discoveries like these in quite a binary way. Either they're a sign of life, or they're not.

But NASA has a much more nuanced take. They recently proposed the confidence of life detection scale, a framework for ordering how likely discoveries actually are to be signs of life based on a set of criteria. It has seven levels, ranging from we found something that could be caused by life all the way to multiple teams have independently confirmed life more than once. NASA hasn't stated where the discovery in the Ezra crater falls, but I'd guess probably somewhere between levels 3 and 4. If the samples come back and independent labs around the world all confirm that what we are

seeing really did come from a biological origin, that would push us up to a level 6. Level 7 might even require going back to Mars and finding the same evidence in a completely different location. So when NASA says this discovery could be the clearest sign of life we've ever found on Mars, they don't mean to say it is clearly life. But the Mars sample return mission could finally reveal whether we've always been alone in the universe or did we once have a cosmic neighbor. Even if our sample turns out to not be life, it's still an extraordinary discovery that will help us understand our own origins even better. See, we think Mars is like a time capsule of an early Earth.

Unlike Earth, Mars doesn't have any continental drift or an active plate tectonic system. Its crust has been frozen in place for billions of years, preserved in a way Earth's crust could never be. The ancient landscapes on our planet have been erased through tectonics, erosion, oceans, and So when we study Mars, we're not just asking whether it once carried life, we're also appearing into a record of planetary conditions that resemble Earth at the dawn of biology. In that sense, Mars is a window into our own origins, offering clues to what Earth might have looked and felt like before life left its mark.

But let's dream for a moment, shall we? What if the sample does turn out to be life? Well, most immediately, it would indicate that Mars was habitable far longer than we imagined, since the sample comes from relatively young sediment. But more importantly, we'd finally answer the question, can life exist on other planets? And in the same breath, open a Pandora's box of follow-ups. Did life on Earth start on Mars, all the other way round? Did a meteor from interstellar space seed life on both our planets?

Or did it arise spontaneously twice? Where else could life exist in the universe? How common is it really? It would also have implications on the Drake equation, a probabilistic formula used to estimate the number of alien civilizations in our galaxy. The FL value here, which stands for the fraction of potentially habitable planets that go on to develop life, would jump from vanishingly small to closer to one. Since two out of two neighboring planets would then have or have had life at some point,

an increase in this value causes the number of civilizations in the universe to shoot up. But crucially, this coefficient only changes if life on Earth and Mars rose independently. If we're related, the products of panspermia, that still represents just one biogenesis event, and the outcome of the equation remains unchanged. There's a concept known as the 0-1-infinity rule. In astrobiology, it represents the idea that life can only exist in 0, 1, or infinite places. We already know it's not 0.

If it's just 1, then we're alone, a single spark in the dark. But if it's 2, Earth and Mars, then why not? 5,000, 5 million, or even infinite places in the universe. Suddenly, life isn't rare. We're not special anymore. And personally, I hope that if we ever discover life out there, it brings us closer together down here. You said this place was steps from the water. We just haven't found the steps yet.

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Spend less time searching and more time actually interviewing candidates who check all your boxes. Listeners of this show will get a $75-sponsored job credit at Indeed.com slash podcast. That's Indeed.com slash podcast. Terms and conditions apply. Need a hiring hero? This is a job for Indeed sponsored jobs. When it comes to the search for life on Mars, we might be looking in the wrong place. Recently I was asked by Timothy Walter on Patreon about the most likely places in the solar system to find life outside of Earth. Mars is certainly a contender.

In the first billion or so years of its existence, Mars was in many ways similar to Earth, and it's entirely possible that life could have emerged on its surface before the planet underwent changes that made Mars much less hospitable. That's why NASA rovers such as perseverance are investigating places like Yezaro Crater, to investigate those dried up deltas for any evidence that life might have once flourished there. But as I looked deeper into the topic, it struck me that this might not be the most likely home for life on Mars.

There is another location that is an even more likely contender for life, and incredibly, that life, if there, might even still be alive to this day. I'm Alex McCulligan and you're watching Astrom Answers, the series where we take questions you post to us on Patreon and uncover the answers. And today, we're going deeper than ever before, into a world where a deep biosphere might thrive. I'm going to answer where I think is the most likely place to find life on the planet Mars. When it comes to life forming though, we should probably start at the beginning. It's worth recognising that we're going to get a little speculative for this video, as there

are many aspects of the origin of life even on Earth that are right now still unknown. I did a video recently on how life likely first came to be, and one of its key points is that there's still a lot of debates over the specifics. It's also worth noting that we do not know for certain that life does exist or ever existed on Mars at all. But there is some evidence that is intriguing. NASA's Curiosity rover has detected methane in Mars's atmosphere, which mysteriously only emerges at night and is strangely absent during the day.

Methane on Earth is mostly produced by living organisms, so it's an intriguing indication that life might be on Mars too. However, this is not definitive proof, as there are also non-organic ways to make methane, I talk about in one of my other videos on life on other planets. So then, why do scientists think that Mars might be, or used to be, the home for life in the first place? It's all thanks to what Mars looked like in the first billion or so years after it formed. According to our best theories of how life first came to be on Earth, there are some key

things that you need. Water for one. All life on Earth seems to need it. But also mechanisms for producing diverse and complex chemical structures, the raw building blocks of life from which protocells could arise. Something like a deep-sea thermal vent would help with that, or possibly a volcanic hot spring, as they would release a nice spew of minerals and chemicals that could then hopefully be formed into very basic proto-cells if conditions were just right.

Generally, on the note of those conditions, you need some kind of selective pressure to choose some chemical structures and discard others. This is quite similar to evolution, in that it wouldn't work if there wasn't a selective pressure to guide it. For animals, this could be a scarcity of food encouraging the survival of those best able to locate it. But for chemical structures, it could be something like a cyclical environment that is sometimes wet and sometimes dry.

to see if certain structures can survive those kinds of changes. The structures that break apart when faced with this stress test are selected out, while those that survive can move on to the next round of selection, a sort of evolution but for rocks. On Earth, evidence suggests that life arose within the first billion years after the planet formed, which is quite fast on the cosmic scale of things, and it turns out that But on Mars, its first billion years of existence, had these key factors, and more. It also had a thick atmosphere and a magnetic field to protect any fledgling life from deadly solar radiation, and to allow bodies of liquid water to form without evaporating away.

It had volcanism, providing energy from the planet's warm core, and those vital chemical building blocks. Sunlight also provided helpful energy to the planet. If the presence of these things on Earth made it Urable, meaning capable of supporting the genesis of life, then it could well make Mars Urable too. However, there's a built-in time limit here. After 1 to 2 billion years, the water had all dried up, Mars had cooled enough that the mechanism powering its magnetic field had ceased, and over just a few hundred million

years later, the atmosphere had been stripped away. This eventually led to the evaporation of all the liquid water. on the planet, with the only remaining water being locked in the ice on the polar caps. So life on Mars would need to have formed during those 1 to 2 billion years after the planet's formation. NASA is working under the assumption that this is the case, and so they've sent rovers and landers to investigate craters like Yazaro for any ancient signs of life. Perseverance has collected 21 rock core samples as of April 2024, which it got from drilling, a few centimeters into the stony surface of Mars.

Yezaro Crater once held a large body of water and a delta. If living things had made that water a habitat, their remains could well have dropped into the bottom of the delta to be captured in the sediment there. There is even a chance that they're still locked into that sediment. Researchers in the journal Astrobiology found that even when completely dried up, frozen, subjected to intense radiation, certain kinds of bacteria on Earth could theoretically survive hundreds of millions of years without too much ill effect, just waiting to be thawed out and given water again. This is why scientists must be so careful about both forwards and backwards

cross-contamination when exploring other worlds. If not there, there is also a chance that life exists in the water and the water. lakes on Mars today. But Alex, I hear you say through your screens, didn't you just tell us that those lakes had all dried up? What I told you was mostly true, but not entirely. While it seems unlikely that there is any water still moving freely on Mars's surface, there is a location where water can still be found, and in liquid form, deep beneath the polar caps. In 2018, scientists announced that they had found an entire lake trapped deep beneath the thick ice. Three more were confirmed by 2020.

This is interesting, because it mirrors an ecosystem on Earth called Lake Vostok, which is also a lake sealed away 4 kilometers beneath the solar polar ice cap. Intriguingly, Lake Vostock was found in the late 90s to house bacteria and even potentially fish. Some trace DNA was captured and brought to the surface. Either way, Lake Vostok is a fascinating ecosystem that has been sealed away for 15 to 25 million years. Sadly, the chance of Mars' lake being another Lake Vostok, filled with ancient life, is actually quite low. Given the temperatures on Mars being so much lower, it's thought that the water inside the polar lakes there have to be very salty.

This would not be conducive for most forms of life. And on top of that, perhaps the Martian lakes are not real after all. A recent study in the journal Science Advances offered other explanations for why the radar imaging saw it saw a lake, suggesting that reflective dust layers spaced closely together could create the same effect, a sort of optical illusion. If this is what's happening on Mars, the lakes might not even be there. So, it seems that Yezero Crater is a big, better place to search.

But even Yazaro has a point against it. Yezaro crater, while certainly habitable, is not a likely place where life could have formed. It does not contain deep thermal vents and isn't home to volcanic springs, unlike other parts of the planet like Columbia Hills. So the question is, could life have formed and then distributed quickly enough that it would make it to craters like Yezero before Mars underwent its transformation into a barren world? It's possible, but it's also possible that it would not.

As the planet cooled and the water evaporated, any bodies of water would have found themselves becoming more and more salty, as any salt concentration would have ended up with a lower and lower ratio of water. Again, too much salt is bad for most forms of life, and research suggests it could have been a massive hurdle for the survival of undeveloped protocells. Such cells simply may not have developed the tools to allow them to survive in such conditions. Even more developed earth life would have struggled when combined with the depleting atmosphere and deadly radiation.

So it's safer to search where life would have begun rather than places it would have distributed. Thus, volcanic spring sites like Columbia Hills already seem like a better place to look for signs of early life than Yezaro Crater. Life never made it out of the primordial soup on Mars, those initial pools are the places that make the most sense to look, as so far we're not looking there. But if you want to talk about where life on Mars might be right now, volcanic springs have one other vital feature going for them. They are gateways to underground biomes.

Why explore out of the water when you can follow those nutrients down to their source? On Earth, life does not just live on the surface. There exists a whole world of life known as the deep biosphere that exists kilometres beneath our feet. Life down there has learned to adapt to living without sunlight and without air in high temperature and high pressure environments. And incredibly, it's thriving. In 2018, Deep Carbon Observatory Collaborators

A group of over 1,000 scientists published that if you added up all the weight of the living things beneath the surface of Earth, it would add up to almost 400 times the carbon mass of every human on the planet combined. The deep biosphere covers an area of nearly 2.3 billion cubic kilometers, almost twice the volume of all the oceans. It contains 70% of all species of Earth's bacteria now kill. Here, also viruses and small worms have been found down there. Overall, it is thought to be as diverse, if not more diverse than the surface.

There has not yet been found a limit to how deep or how hot life can survive, as records are continually being broken. Currently, the hottest survive temperature is 121 degrees Celsius, hot enough to boil water, which was found with a bacterium living in a thermal vent. And the deepest is 10.5 kilometers beneath the sea level. Food is hard to come by when your kilometers deep in rock and metabolic processes of living things in the deep biosphere is 10,000 to 1 million times slower than the surface.

With life ticking so slowly, it transpires that they can live almost indefinitely. We don't yet know how old things get down there. Some species are found at sites globally, suggesting that although they're travelling through solid rock to do so, bacteria are still somehow able to get around. We've only in the last decade begun to grasp the sheer scale of the deep biosphere on Earth, but all of this is incredibly insightful when it comes to life on Mars. Deep beneath Mars's surface, life could be well protected from any of the devastation going on at its surface.

Life is proven to be able to survive thermal vents, which means that once life formed in a volcanic region, it would have been able to seep into the warmer, nutrient-rich subsurface through cracks. It simply would have had to fall down. And given the long metabolisms involved, it could still be alive there today. There could be a thriving, widespread ecosystem alive and well. Finding out for sure would be difficult. We find it hard to explore the deep biosphere here on Earth, requiring deep sea drilling technology or very deep mines.

On Mars, landers like insight struggle to even dig two to three centimeters. But to my mind, that's the most likely place to search for Martian life today. Of course, it's worth reiterating that there are a lot of ifs here. If life formed on Mars in the first place, if it managed to make it out of the hot springs it likely formed in, if it evolved and adapted like it did on Earth, only then could it still be out there. But it's incredible to me to consider that while Mars's surface might appear dry and barren, there's the potential for an entire thriving ecosystem beneath Mars' soil alive today.

that is the cause for the methane in Mars's atmosphere, detected by curiosity. There's always a chance life spread to legs like Yezero, but my bet, if it's alive today, it will be deeper. I believe that when it comes to finding life on Mars, we've barely scratched the surface. Do you have a question you'd like us to answer? Send it over to us on Patreon, and you might be selected for a future Astrom Answers episode. But for now, thanks for watching and I'll see you next time. The universe is a harsh, brutal place.

Solar winds, high radiation and extreme temperatures and pressures make it largely inhospitable. And yet, life found a way. It's in you and in me. And perhaps there is no quest more epic than the search for life beyond our beautiful blue home. But scanning the night sky for possible neighbours, like most things in astronomy, comes with its challenges. Where could they be? What would they look like?

Should we even look for them? Are they, in turn, looking for us? One thing that makes the search for alien life tricky is that we don't know exactly what we're looking for. But by studying ancient life forms on Earth, scientists can get a clear idea of the kind of organisms that are most likely to be out there and where we might be best off looking. I'm Alex McColgan and you're watching Astrum.

Join me today as we uncover how scientists actually hunt for alien life, the unique characteristics of Earth's earliest life forms, and the surprising role these ancient microbes play in guiding the quest to answer the eternal question. Is there anybody out there? If you were tasked with combing through a seemingly infinite universe for science of life, where would you start? I reckon I'd start by looking for a planet similar to ours. Starting the surge in the most hospitable part of the galaxy seems like a smart move.

The galactic habitable zone is the region of a galaxy that has the most optimal conditions for potentially life-bearing planets to develop. Typically, it's a spot with enough heavy elements for Earth-like planets and minimal cosmic drama like supernovae or stellar close calls. This excludes stars too close to the center or in the spiral arms of galaxies, since they are full of super intense harmful radiation. So far we've discovered 5,539 exoplanets, of all different shapes, sizes and compositions. Scientists are still debating what kind of atmospheres might be hiding signs of life on other

planets. As far as we know, life on Earth emerged 3.8 billion years ago. At that time, our atmosphere was mainly nitrogen gas, carbon dioxide, and water vapor. You'd understand then why some scientists choose this atmospheric composition as a preferred focal point. But others aren't so convinced. They say only searching for these compounds is limiting, since methane and hydrogen gas atmospheres may themselves be signs of life.

In reality, it seems to be a bit of a chicken egg situation. The atmospheric composition of a planet determines what kind of life, if any, could emerge on that planet, but the kind of life that emerges also affects the composition of the atmosphere. Let me quickly explain with an example from home. Today, Earth's atmosphere is 21% oxygen. That wasn't always the case. It wasn't until about 2.4 billion years ago that free oxygen gas started accumulating in our atmosphere.

This is known as the Great Oxidation Event. The main theory among researchers is that cyanobacteria, living in the ocean, evolved the ability to photosynthesize, and started releasing oxygen gas faster than it could react with other compounds. Eventually, this oxygen evaporated from the oceans into the atmosphere, replacing the methane that was already there. This is an example of a biosignature of life, the next step in honing our mission to find alien life. Biosignatures are substances, signals, or patterns that could be a sign of biological activity.

This could be as obvious and direct as a fossil, or something more subtle like the composition of the planet's atmosphere. They are important because they indicate not only the potential presence of life, but also the level of its sophistication. It's important to understand that all biosignatures are really just potential biosignatures. Because while they could be signs of life, they could also be caused by non-living things. A big challenge scientists face is battling all the false positives that arise. There's no official classification system for biosignatures, but it's useful to think about

them falling into three categories. Gaseous, temporal, and surface signatures. Gaseous biosignatures are direct or indirect products of metabolic activity. The most common manifestation of this is the composition of the atmosphere. For example, the presence of haze could be an indirect byproduct of a methane-rich world. This could tell us that a particular planet hosts microbial life similar to what we had on Earth over 2.5 billion years ago before the Great Oxidation Event. It's similar to the example we explored earlier of how having free oxygen in the atmosphere

could be a biosignature for photosynthesizing life. Temporal biosignatures are time-bound changes that can correlate with biosphere activity. On Earth, the concentration of carbon dioxide in the atmosphere rises in falls with the seasons. Vegetation grows in the spring and decays in the autumn. This oscillation is way stronger in the northern hemisphere than the southern hemisphere, because it has more land mass. In theory, we can use this kind of information to see where on an exoplanet life is most likely

to be. However, nothing is so black and white. Temporal biosignatures can be caused by abiotic factors too. The concentration of methane in Earth's atmosphere, for example, changes mainly due to its interaction with water vapor in the troposphere. So even though the methane itself is from a biological origin, the temporal oscillations are dictated by abiotic factors. I personally find surface biosignatures the most interesting.

Basically, every planet reflects some light from its star. Different materials on the surface of the planet will reflect different combinations. of wavelengths of that light. This results in a unique reflectance spectrum for every material. Surface features like rocks, snow, water, and soil can all be deduced from a reflectance spectra. Life can also influence the reflectance spectra of a planet. This is an example of a surface biosignature.

Here's where it gets super cool. Today, the Earth appears blue from space because its oceans reflect a lot of blue light. But some scientists think that there was a time when our planet would have been purple instead. There's an ancient family of microbes that produce a protein called bacterioroidopsin. Bacteriorodopsin can create energy without a carbon source, something plants can't do. It literally just turns sunlight into metabolic energy the cells can use. use. It is thought to be one of the simplest and earliest bioenergetic processes to have developed. But why would it make Earth appear purple? Bacterio-rodopsin contains a pigment that reflects

a lot of purple light. This makes its cell membrane appear purple. An early Earth would have had oceans full of this organism, turning the whole planet visibly purple. While it's just a bit of fun to imagine a purple Earth, the implications of this theory mean that these microbes, and others like them, could be a very useful surface biosignature of exoplanets. Of course, the reflection of purple light alone doesn't mean much. But if it were to be combined with evidence of a highly saline surface, that could start to paint a more convincing picture. You see, the specific family of ancient microbes that produce this purple protein are called

halophilic archaea, or hallo-archia for short. Archaea are some of the most ancient lineages of life on earth. Even though they're single-cell organisms, they are not to be confused with bacteria. The two are actually totally different domains of life, but we won't go into that. Hallophilic means they grow and survive best in conditions of extremely high salinity. Hallophiles belong to a large group of organisms known as extremophiles. Extremophiles are life forms that are able to live in very hostile environments. There are lots of different kinds of extremophiles that are well adapted to different kinds of extreme conditions, like very high or very low temperatures, pressures, dryness, radiation,

salinity, and heavy metals, or any combination of those extreme conditions. These organisms span the globe, inhabiting the harshest parts of our world, from sulfuric hot springs in Japan to the Atacama Desert in Chile, to sewage treatment plants in Germany, and even a hyper-salin deep lake in Antarctica, where our beloved Halo Aquea were found. What makes extremophiles so interesting is their unique biology. As you can imagine, living in such extreme conditions forces you to get creative. Extremeophiles' biochemistry and physiology are often modified in very clever ways to help them adapt to their harsh environments, and this makes them an astrobiological gold mine.

Many extremophile habitats on Earth are surprisingly similar to conditions on other planetary bodies. These regions on Earth are called analogues, and they can teach us a lot about where we might find life beyond our home planet. For example, the Atacama Desert in South America is a very arid environment with high salinity, high UV radiation levels, and oxidizing soil, making it quite similar to Mars. In fact, we've been studying it as an analog to Mars for years. Life has been found across the Atacama Desert, but its presence is highly patchy. In a way, this is good news.

It helps scientists identify the exact factors that cause life to appear where it does. And therefore, where we might have the best chance to find it on Mars. The extremophilic yeast, Exofialla, is another example of this. It was found in high altitude regions of the Atacama and caught the attention of astrobiologists pretty fast. Researchers were looking at how Exofiala's protein expression changes in a simulated Martian environment. After the first 24 hours of exposure, they found some proteins but also.

over-expressed and others under-expressed compared to baseline levels. However, there were no signs of heat shock proteins. The compounds organisms release in response to high-stress conditions. Even more surprisingly, seven days into the exposure, Exofialla's protein expression patterns were back to normal. This is a big deal, because it indicates that exofialla is able to recover and survive under Martian conditions. In other studies, Exofialla showed great resilience to the Earth's stratosphere. It also showed the highest UVB and UVC resistance when compared with other similar yeast. All this together makes it a promising model for potential life on Mars.

It may be a stretch to suggest, but it is possible any Martian life we might find could be biochemically similar to this humble yeast. species of Hallowarchia are also being studied as exciting astrobiological models. Specifically, Hallobacterium NRC1 and Hallobacterium Lackus Profundi. They are both extremophiles that thrive in high salinity and are great candidates for understanding potential life on Mars and Jupiter's Moon Europa. Think about it. If there is a planet where conditions are totally different to ours here on Earth,

It makes sense that the life we may find there could be completely different. But if the planet does have similarities to our own, is it really so crazy to think that life there might look similar to? Mars is a specific focus for our search for life, because it has several similar early geological processes to Earth. Scientists have determined that Mars was possibly much warmer and wetter in its history. This suggests there could have been super salty brines on early Mars. Like we've said, these hyper-salien environments are ideal for hallo-Aquia.

Wouldn't it be cool if these ancient microbes could have been enclosed in Martian brines lying dormant all this time? Similarly, Europa is thought to contain salty oceans two to three times the volume of Earths below its inhospitable surface. This subterranean ocean might also be chemically rich thanks to a silicate sea floor and surface oxidants, making it a great candidate for halophilic life. In fact, scientists have been testing this theory by shooting Hallowakir into space since 1994, testing to see the types of harsh environments they can survive.

The first mission involved the ejection of a capsule into low Earth orbit. The short-term exposure results were promising, with the microbes surviving the initial exposure. The European Space Agency then designed the Expose facility for the short-term exposure. medium and long-term exposure experiments on the outside of the International Space Station. Three separate missions were launched in 2008 and another in 2014, testing survival of various halophilic archaea strains in space. In March 2019, results emerged from the ESO's Biomex experiment. They reported that microbes from Earth survived 18 months of space exposure outside the ISS,

suggesting life could theoretically survive on our neighbor, Mars. Clearly, there's still a lot we don't know about these microbes. For a start, they've only ever been studied in isolation. How would they interact with a wider environment? All the research so far has focused on sodium chloride, but how would these organisms fare in other salts? So even though they seem like promising candidates with lots of potential, more research is needed to fully up.

understand their implications for astrobiology. So, how does knowledge of these ancient microbes turned astrobiological models help us in the search for life in the universe? Well, within our own solar system, having intimate knowledge of these organisms can directly impact where we send our space missions. For example, the Spirit rover was sent to the Gustav Crateer to investigate a suspected ancient lake. We already had lots of evidence for voicembs of volcanic hydrothermal vents on Mars, but Spirit discovered lots of new evidence pointing to hot spring activity in Mars' past. Hot springs are great places to look for biosignatures because they can preserve ancient cells

in their chemical precipitates for a long time. It would be an ideal place to find fossils of Martian organisms if they ever existed there. Beyond the Kuiper Belt, studying extremophiles lets us better understand how life arises and evolves in the universe. Firstly, it can show us what traits to look for in distant planets, a certain spectral fingerprint, or a particular gas in the sky. It also indicates what the signals we receive from distant planets could mean about how hospitable they are. Extremophiles show us what type of life we might expect on other planets. And finally, they push back the limits of life as we know it, to redefine what is possible time and time again.

Kayak gets my flight, hotel, and rental car right, so I can tune out travel advice that's just plain wrong. Bro, Skycoin, way better than points. Never fly during a Scorpio full moon. Just tell the manager you'll sue. Instant room upgrade. Stop taking bad travel advice. Start comparing hundreds of sites with kayak and get your trip right.

Kayak, got that right. This is a Bose moment. You've been there before. somebody's apartment, small talk that's going nowhere, plastic cup that's almost empty, it's not great. Then someone hits play on a Bose speaker. Heads nod, feet tap, one person dances than everyone does. Awkward becomes electric. When Bose sound fills the room, you don't just hear the music. You feel it. Your life deserves music. Your music deserves Bose. Find your perfect product at bows.com. Our searches for signs of life haven't been very fruitful yet, and will

likely take many decades more. Designs are already in the works for a new generation of telescopes that will take to the skies in the 2030s and 2040s. The Nautilus is a concept telescope that could be operational by 20303 and would enable scientists to cover 50 times the light collection area of the James Webb Telescope thanks to its large aperture. Another concept, put forth by NASA, is designed to observe potentially habitable exoplanets around sun-like stars. The habitable exoplanet observatory, or Habex for short, would look for biosignatures like water and methane.

It would also become the first telescope with the ability to directly image an Earth-like exoplanet. They sound fascinating. I hope they get approved. We've come a long way and still have a long way to go, but we are not giving up our epic mission to find other life forms and their homes beyond the bank. of our planet. Our distant relatives will just have to wait a little longer to be found. Life is a mysterious thing. As far as we are currently aware, Earth is the only place in the

universe where life exists. Life is so prevalent on Earth because of a combination of many factors, including Earth's distance from its star. It is situated in the solar system's Goldilocks zone in a region that is not too hot or too cold. We also have a magnetic field that protects us from solar and cosmic particles. We have an oxygen-rich atmosphere which we can breathe. We also have an abundance of water on the surface. These and a few other factors combined allow life to exist as it does here. But a quick look around the solar system reveals nothing on the surface of any

celestial body that is even close to resemble the green and blue lush surface of Earth. So does this mean there is no life in the solar system? Well, the simple answer is, we don't know, but there are a few places we are still interested in checking out, just to be sure. I'm Alex McColgan and you're watching Astrom, and together we will travel through the solar system and see where the most likely places to find life could be. Here's our sun. It's a very nice and stable type of star known as a G-type main sequence star.

Not a good place to look for life, as far as we know, though. Certainly nothing like life on Earth could survive the thousands of degrees temperature on the surface. We would have to expand our concepts of what life could be, perhaps beings of energy rather than traditional elements. Neil deGrasse Tyson said he wasn't opposed to this idea. I don't see why not, except, oh, by the way, masses, energy, energy, is mass. So I can imagine an alien species that is energy. I can imagine it. Like a pound of energy. I can allow my brain to accept the possibility. However, the possibility is extremely remote,

so I think we can leave the sun and move safely onto Mercury. Mercury does not tick many boxes in regards to what would be needed for life to form. It has a very tenuous atmosphere and is far too close to the sun. This combination means that the The temperatures on the day side rise to over 400 degrees Celsius, and the night side can drop as low as minus 170 degrees Celsius. It has been discovered that Mercury was geologically active in the past, but the last eruption was thought to be 1 billion years ago. Many extinction events would have happened during Mercury's history that would have most

likely prevented life from getting anywhere. There is water ice to be found in the permanently dark craters around the sea. the planet's poles, but we theorise that only liquid water can support life. Mercury seems to be a dead, inactive and sterile planet. The next place to visit is Venus. Venus does have a rather substantial atmosphere, but the problem is that it isn't quite far enough away from the Sun to be in the Goldilocks zone. On Venus's surface, it is even hot the Mercury, well over 400 degrees Celsius all over

the planet. This is due to the greenhouse gases in the atmosphere. Carbon dioxide make it up 96% of it. This heat means that water could not stay in liquid form on the surface. There is a slight possibility, however, that there could be some form of microorganisms high in the clouds of Venus that would use UV light from the sun as an energy source. The temperature and pressure high in the atmosphere is much more hospitable than on the surface, so this possibility exists. But moving on, one of the best bets in the solar system is Mars. It is situated nicely in the Goldilocks zone and has an atmosphere. The big problem with Mars though is his lack of a magnetic field.

The magnetic field on Earth prevents the solar wind from the sun stripping away the particles in the upper atmosphere. upper atmosphere. Because Mars doesn't have this, its atmosphere has been stripped of all but the heaviest molecules, consisting of 96% carbon dioxide. At one point in its history, it did have some surface water, as can be evidenced by dried up rivers and lake beds. However, today that water has gone, and if there was any life on the surface, this is most likely gone too. Scientists have been keen to find evidence in rocks with the Viking missions, and that have been Viking missions and looking for methane in the atmosphere with the rovers currently on the planet, but they have so far found only traces of evidence.

But NASA are not deterred, finding solid evidence of life on Mars is now one of their primary objectives, so they clearly think there's still a good chance of finding something. There are a few telltale signs that life exists or could have existed on Mars. There are possible biosignatures like methane in the atmosphere. often the byproduct of life. Scientists can't quite agree on where the quantity of methane gas comes from, and life is a definite possibility. We also have 34 meteorites on Earth which originated from Mars.

These are highly valuable, as they are the only samples of Mars that we possess. A few of these meteorites even contain what looks to be fossilized bacteria, although they are much smaller formations than any terrestrial bacteria. bacteria on Earth. Sadly, this is not conclusive evidence, as these formations could also be explained by natural processes. At this point in time, there are a couple of possible places to find life on Mars. One would be about 10 meters under the surface. Water can be in liquid form this far down, and any life would be much more protected from cosmic and UV radiation. The other theory is that microorganisms could exist under the polar ice caps.

Potential evidence of this could be the darkening of these spider patterns next to the geysers on the poles. The darkening could be these microorganisms as they photosynthesize the sun's UV light from under the surface. But with all the attention Mars is getting from the global scientific community, I guess that we will know conclusively whether there is life on Mars within the next 30. years. I'm happy to announce we have a weekly newsletter to keep up with all the discoveries in our cosmos and our designer Peter has made the most beautiful email you'll ever receive. Sign up

with the link down below. It's the best way to stay connected between videos, short, focused updates on what's new and fascinating in space each week. No spam, no filler, just the good stuff. You'll get the latest news, visuals and insights delivered straight into your inbox. If you enjoy Astrum videos, you'll love this. Join the newsletter and stay curious with us. If you used Babel, you would. Babel's conversation-based techniques teaches you useful words and phrases to get you speaking quickly about the things you actually talk about in the real world,

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