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The planet Mars has stirred the imagination of scientists and space enthusiasts for hundreds of years.
So Mars has blue sunsets because of the difference in atmospheres and the amount of dust and things like that.
Although Mars doesn't have those sandstorms from the Martian, it has really cool dust devils.
That's Hemani Kalucha.
She's a planetary scientist who recently completed her PhD at Caltech.
And she's spent a lot of time thinking about Mars.
You could think of like the American Southwest as a good analog.
Like if you were to walk through Utah.
That really reminds me of what we see from the rover and what it would feel like to walk around Mars.
Occasionally, in the distance, you would see these giant volcanoes like, bigger than the size of Mount Everest.
Many people, including Hamani, have wondered, was there life on Mars?
And the more Mars is studied, the closer scientists get to answering that question.
The more we learn about Mars through all of the rovers, the more it seems like ancient Earth.
It had these fantastic big rivers flowing and big deltas flowing and lakes just like Earth that were really big.
And it was this wonderfully wet and alive world.
Using the Perseverance rover, Hamani studies the Martian surface, looking for evidence of ancient life.
Anything that might have lived in those rivers and deltas billions of years ago.
Mars looks very different now.
Whenever we get pictures back from the rover, it's always this red-hued layer of dust that's on all these rocks.
And they're sort of broken up by a long history of it being cold and hot and broken up and fractured.
And so a lot of their original glory doesn't remain.
In what does remain, scientists think there could be traces of what ancient life has left behind.
No human has been to Mars to look for these clues, which is where rovers come in.
The Perseverance rover has been roaming across the Martian landscape for more than four years.
As it was driving through dried-up riverbeds, it saw something on the rocks that has scientists, including Hamani, excited.
Something that will get humanity the closest it has ever gotten to evidence of life on Mars.
That something?
Spots on rocks.
Today on the show, life on Mars.
How tiny specks on rocks could be the most convincing evidence of a once-living Mars.
I'm Regina Barber, and you're listening to Shorewave, the science podcast from NPR.
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Okay Hamani, it really does seem like every few months there's this new headline about life on Mars.
What is the evidence that's kind of been stacking up that there most likely was life on Mars at one point?
So the first was that when Curiosity rover was exploring the lake sediments of Gale Crater, it found organic matter rich sediments.
And those are really exciting because, as we know, life likes to leave behind organic matter.
And obviously, there's other ways for organic matter to land on Mars.
It can come in through meteorites.
But that was sort of the first detection of organic matter.
And then the second sort of big discovery from Curiosity I would say is that as the rover traversed higher and higher up this mountain that it's climbing... we continued to find lake sediments and sediments that had experienced water alteration.
And that sort of means that it wasn't just water for a quick second in a lake that immediately disappeared.
It was long-lasting water.
And that's what you really need for life to actually develop, to go through all those steps from organics to becoming a cell, to actually thriving for all this time.
And so long-lived water is a really, really exciting discovery.
Cool.
All right.
So the most recent rover, what has Perseverance found?
With Perseverance Rover, we came over to Jezero Crater and it landed in 2021 and we were exploring this delta for many years.
And then we sort of exited the delta and went into this ancient river channel and we found these millimeter-sized spots.
And the spots are really exciting because they're really intricate features.
Some of them look like poppy seeds on a bagel.
Some of them look like small leopard spots.
Some of them are green spots with these black tendrils.
And they look like something that ancient life on Earth leaves behind.
We've seen it in the rock record on Earth.
So that was the most exciting recent discovery.
In your opinion, out of all of those, what's the strongest evidence that there was once life on Mars?
The spots are definitely the most exciting discovery, because the key difference is you can have long-lived water and life doesn't have to proceed.
You can have organic matter.
Life doesn't have to thrive in it.
The spots are the first thing we've seen that life may have actively made or left behind, instead of just a condition that allows life to happen.
Okay.
So, Hamani, these spots, they do exist on Earth, right?
And those spots came from living things.
How do these spots on Earth form and what do they look like?
So when rocks are sitting in water for a long time on Earth, or then exposed to air for a long time, they get rusty, just like garden tools sometimes when they're sitting out in the shed for a And so the way that these spots form is that the microbes essentially eat a whole spot of rust and leave behind what we see just like a caterpillar sort of eating out a piece of leaf.
What?
I love this.
Yeah.
It is very easy to visualize.
Okay.
But, like, that's not the only way these spots could have formed on Mars, right?
There could have been other things that made these spots.
They might not have formed by ancient bacteria.
Yes.
So in addition to ancient bacteria, sometimes you can just have organic matter laying around that when the rocks are heated up it sort of leaves behind these spots.
You can think of like steam rising through some grates and leaving behind the pattern, essentially.
So why is this so convincing that it's not that?
Like that it's not heat and it is maybe a microbe?
So there's a couple different lines.
One is there's so many different variations that we're seeing.
And life likes to be variable and not homogenous.
And anything that's not life is usually pretty homogenous.
The other reason is that the minerals that are left behind in the spots are also things that life likes to leave behind.
And so that's another way that we sort of look for ancient life, is we look for specific minerals that we know ancient life on Earth likes to leave behind?
Okay, so you're telling me there's a few reasons why maybe the easiest explanation for these spots is ancient life.
Location is one of them.
Can you tell me about that?
Yeah, so we, interestingly, find these spots across the whole river channel.
Which is really exciting, because if they were just next to a heat source or something like that, you might be more suspicious.
But the fact that they're found everywhere and in these different forms, and usually life likes to leave behind intricate stuff.
So the tendrils in the green spots, for example, are really intricate things.
Tell me why the color, like some of these spots are green.
Why would that color be important for life?
Yeah, so rusty rocks are all red, and so that's sort of the background of red that we're looking at.
But you could think of how a penny starts out brown and then rusts to green.
Well, iron rusts to red, but then when it's reduced back, it goes to green.
And so we're seeing a change in iron, but just in the little spot.
We're not seeing it everywhere.
So that points to a really specific process.
And you had talked about these leopard spots and poppy seeds.
So is the shape of these spots important?
Yes, absolutely.
Because you can think of minerals.
You might have seen the gem collection at the Natural History Museum.
They're very regular in their shape.
They're crystals with very definite shapes.
And these spots are not that.
They've got flimsy borders and squiggly lines and all the sorts of things that point to life.
What's the ideal next step, though?
Like if you Hamani had all the money in the world.
What would you do next to verify that there was indeed like ancient life on Mars?
Yeah.
I mean, there's only one thing to do.
We would collect a core of these and we'd bring them right back to Earth as soon as possible, revive Mars sample return and then put all of our laboratory instruments on them and just see what was there.
If Mars sample return miraculously happens and we get these cores back, what would we have to see in that microscope to tell us yes, there was ancient life on Mars?
Yeah.
So with the rover, we can see pretty small things.
We can see millimeter-sized things.
But with our microscopes on Earth, we can see micron-sized things, nanometer-sized things.
And so we could see the mineral shapes down to the micron, down to the nanometer, and we could see the organic matter that's maybe trapped within there.
And the type of molecules that would be in there would tell us something.
We could measure the isotopes of these minerals to really accurate degrees and see if they point to something life has made.
There's a whole host of tests that we could do.
Is it possible that we would actually see an organism like a fossil?
On our luckiest day, but we might not be so lucky.
Because these things are so old, they tend not to preserve the microfossils.
And even on Earth, these types of spots don't tend to preserve microfossils.
Okay, got it.
So yeah, we have to look for other signs and it's a bit like detective work and it's really old detective work, so it's not always clear, but it's worth trying.
Why does it matter that maybe there was life once on Mars?
I was actually at a wedding recently and I was asked the same thing.
So I feel I'm prepared for this.
It's kind of not about Mars, really.
It's not about one specific place.
It's the concept of are we alone in the universe or not?
And you could say well, you know, that doesn't affect my taxes and it doesn't really change anything about my day to day life.
But it's kind of like why poetry matters or good writing heals you and things like that.
It's the art of finding these questions is something worth living for.
Hamani, thank you so much for talking with us today about the possibility that there was life on Mars.
Anytime.
It's my favorite thing.
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This episode was produced by Burleigh McCoy, edited by Megan Cain and fact checked by Tyler Jones.
Kwesi Lee was the audio engineer.
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I'm Regina Barber.
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