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Last week, NASA did a thing that, for us in the science communication world, is always
a little bit of a mixed bag.
They were like, “We’ve got some really big Mars news,” and then the entire world
goes crazy and there’s like, “There’s life on M...!”
And then you’re like, “No, they probably would do this a different way if there was
life on Mars,” but we’ll listen, and it will be exciting, but probably not in precisely
the way you’re thinking.
And it was cool!
But let’s get this out of the way in the beginning: The Curiosity rover did not find
evidence of past or present life on Mars.
And when the headlines said ‘Organic Matter on Mars’, for non-science speakers that
can be confusing, and they’re like, “So, like, organic matter like a little bit of,
like, snot?
Like, what is this on Mars?”
No, it’s carbon compounds.
If there was life on Mars, you would find out about it in a really big way, I promise.
And we’d be here.
But, Curiosity did find even more evidence to indicate the planet could’ve been habitable
billions of years ago.
The results came in two papers published last Friday in the journal Science.
And while they don’t prove anything about life on the Red Planet, they do show some
of the strides Curiosity is making in understanding Mars’ history.
Since it landed on Mars in 2012, Curiosity has been hanging out in Gale Crater, which
planetary scientists are pretty sure is an ancient lake bed.
Among its duties, the rover has been drilling into rocks and sniffing the atmosphere to
detect organic molecules.
These are carbon-containing compounds that, on Earth, are often produced by life.
So finding them on Mars might suggest life once existed there, too, although they can
also be made by non-biological processes.
A key one is methane.
We’ve known that there’s methane in Mars’s atmosphere for a while.
But now, Curiosity has shown that the amount, at least in the vicinity of Gale Crater, varies
seasonally.
In the northern hemisphere, it peaks in summer months and drops near the winter.
The paper’s authors suspect the variations come from methane being stored deep underground,
and from temperature changes on Mars’s surface that allow it to flow upward.
For example, the gas could get trapped underground in icy crystals called clathrates, which melt
come summer to free the gas.
At the moment, it’s impossible to know if this methane comes from biological or non-biological
sources.
But we do know it’s getting replenished somehow.
The molecules only survive for a few hundred years before sunlight breaks them down, so
something has to be making more methane.
Even if there is no life producing it, though, this is still very cool news.
For one, Earth’s atmosphere doesn’t have a seasonal variation of many molecules, so
Mars gets to be kind of special that way.
Also, if the variation does come from geologic processes, it would mean that Mars’s interior
isn’t as dead as we thought.
There would likely have to be some kind of heat source down there to drive those methane-producing
reactions.
So it’s probably not aliens, but it’s probably some very cool geology.
And that’s the result of one of the papers.
The other involved organic molecules more complex than methane.
A few years ago, Curiosity ran tests that suggested larger organics existed on Mars’s
surface, but the data was contaminated by other chemicals.
Now, we have some clearer results.
Curiosity found these new compounds by drilling into 3.5 billion-year-old rocks called mudstone.
Mudstone is a sedimentary rock that forms from silt accumulating at the bottom of a
lake.
Unlike other rocks on Mars, it’s likely a better place to store organic compounds.
Now, this could be because of a few reasons, including, like, protective interactions with
other molecules.
After Curiosity powderized and extracted the samples, its tool suite, called SAM, heated
them to more than 500°C.
That was more than enough to get them to release their organics.
Then, SAM could analyze exactly what molecules came out.
Some of the compounds identified included thiophenes, benzene, toluene, and small carbon
chains.
But they likely started off as something else.
See, Curiosity collected its samples from less than 5 centimeters below the ground.
Anything that close to the surface is affected by radiation from space, which, along with
other chemicals in the dirt, breaks down organic matter over time.
So most likely, the compounds Curiosity found are really pieces of larger organic molecules,
although we don’t know what they started out as.
If it were capable of drilling farther down, where radiation isn’t a problem, maybe the
rover could have found some of the original organics.
But the fact that some bits and pieces survived long enough to be detected reveals that Gale
Crater might have once held all the necessary chemical building blocks for life.
Whether or not life actually existed, though, that’s still up in the air.
Just like the methane, there’s no way to know where these organic molecules came from.
Many of them are found elsewhere in the solar system, like in interplanetary dust and on
meteoroids.
So it could be that Curiosity happened to find the remnants of a meteorite impact, not
of life.
At a minimum, the study shows that traces of Martian organics, whether they come from
tiny Martians or just chemistry, can survive for billions of years, to some degree.
Luckily for us, we have a lot of future missions planned that can help us dig into that matter.
Or, rather, drill into it.
NASA’s InSight lander, which launched back in May, will land on Mars in late November.
While it won’t be able to determine chemical compositions, it will be able to drill down
farther than ever before: 5 meters, to lower a heat probe.
So it might be able to help us figure out some of that seasonal methane puzzle.
Also, the ESA’s ExoMars Rover is slated to launch in 2020, and while it will only
be able to drill down 2 meters, it’ll have the tools to extract rocks and analyze what
they’re made of.
So hopefully, the fact that it will be able to go, like, 40 times deeper than Curiosity
means we’ll be able to find more intact organic molecules.
Finally, NASA’s 2020 Rover won’t be doing any deep drilling, but it will have technology
to hunt for and understand any Martian organics it comes across on or near the surface.
So hang on you tiny, probably dead Martians!
If you ever existed, we’re coming for you!
Thanks for watching this episode of SciShow Space!
If you’d like to keep following the latest discoveries in astronomy and planetary science,
we make a news episode like this every Friday!
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