Chapter 1: What is the main topic discussed in this episode?
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.
Chapter 2: What recent discovery suggests life on Mars?
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 Jezero 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 Jezero crater seems like a good bet. 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 2024, while exploring the edges of the ancient Neretva Valles 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 saw something amazing.
The rock, also known as Chiava 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 micrometres to 1 millimetre 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 localised 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 centre 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 metabolise iron instead of oxygen. They take in iron oxide and release iron as a waste product. The energy given off by this reaction then powers their metabolism, a process known as chemosynthesis. When the expelled iron-2 reacts with the phosphate and water in the environment, it forms vivianite.
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Chapter 3: What did NASA's Perseverance rover find in Jezero Crater?
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, olivine doesn't have strong silicon-oxygen-silicon bonds.
Instead, it's made up of negatively charged silicate 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 orthosilicic 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 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 labelled with radioactive carbon-14. If microbes were present, they'd metabolise 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 perchlorate, 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 84001 made headlines.
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Chapter 4: How do scientists identify potential signs of life on Mars?
And that was before we discovered this potential biosignature on our neighbouring planet. All we can do is hope this puts political pressure on leaders to mobilise 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-handed, 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. Carbon comes in a few different flavours, 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 7 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 Jezero 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 neighbour?
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 volcanism. So when we study Mars, we're not just asking whether it once carried life, we're also peering into a record of planetary conditions that resemble Earth at the dawn of biology.
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Chapter 5: What are the implications of finding organic compounds on Mars?
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 Jezero 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 McColgan, and you're watching Astrum 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' 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, as 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 protocells, if conditions were just right. Finally, on the note of those conditions, you need some kind of selective pressure to choose some chemical structures and discard others.
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Chapter 6: What challenges do scientists face in proving life existed on Mars?
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 clearer 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 search 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 centre 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 vapour. 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 photosynthesise 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 a planet's atmosphere.
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