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Rovers like Curiosity search for life on Mars using rock and soil samples, but why don't they examine liquid or frozen water?

Hosted by: Caitlin Hofmeister
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[♪ INTRO].

Sometimes you hear stories in the news about how we found frozen or maybe even liquid water on Mars. And those stories are always fun to get excited about because, if Mars is anything like Earth, there might be alien microbes in that water.

But you may have also noticed that we’ve never actually sampled any of the water. And it’s not because of some global conspiracy to keep the public from finding out about aliens. The real reason we haven’t studied water on Mars is because almost nothing we’ve sent there is sterile enough to do it.

Nearly every spacecraft we’ve sent to the Red Planet has carried thousands of microbes with it, which could infect any water we tried to analyze. We haven’t contaminated the entire planet or anything. But to really search for life on Mars, our sterilization skills are still gonna have to get a whole lot better.

Ever since we started going to the moon, scientists have been taking precautions to avoid forward contamination, or infecting the rest of the solar system with microbes from Earth. To sterilize a spacecraft, engineers use variations of the methods you might think of, from wiping parts with alcohol to baking it with extreme heat. So, we do try and keep things squeaky clean, but it’s not easy.

For one thing, sterilizing a spacecraft takes a lot of time and money. But no matter how much we spend, it’s almost impossible to get rid of all microbes, since our world is full of them. To make this process more cost-effective and efficient,.

NASA has created different tiers of sterilization. So based on where you want to explore, this policy allows some spacecraft to have more microbes than others. For example, if you want to send a probe into the Sun, where there is definitely no life, your mission can harbor as many microbes as you want.

But if you want to go to Mars, the standards are a lot more strict, because there could be life there. But there’s still some wiggle room. Like, if you want to go to the planet just to study some cool, totally dead rocks, your spacecraft can have up to 30,000 microbes on it.

And that might sound like a lot, but for comparison, your computer mouse probably has more than twice that. And a spacecraft is a lot larger than your mouse. Allowing up to 30,000 microbes still keeps Mars safe, because research suggests that none of those microbes will survive long enough to establish a colony.

They’d likely be killed off by radiation from the Sun first. It also means companies don’t need to spend millions of dollars to make a perfectly sterile spacecraft, which is a nice bonus. This is the category that our rovers, like our sweet little Curiosity, fall into.

So, really, it’s not a surprise that Curiosity couldn’t go splashing around in puddles, because no matter how much water we find on Mars, that’s just not how it was designed. Instead, Curiosity was built to figure out whether or not there could have been life on Mars using rock and soil samples. It wasn’t testing to see if there was life in those rocks, just if they suggested that there could have been the right conditions for it.

So as long as we don’t let Curiosity near any liquid or frozen water, a few microbes are totally okay. If we did want to sample water on Mars, or check out any other regions with a high probability of life, we’d have to make a much cleaner spacecraft. It could only have 30 microbes on the entire thing, three zero, which seems basically impossible.

But there are some ways to do it. One method is to use what’s called a dry-heat cycle, or baking, where you expose the spacecraft to temperatures around 125 degrees Celsius for 30 hours or so. That’s enough to kill some of the most stubborn microbes.

That’s what we did for the Viking landers in the 1970s, back when we thought there was a chance all of Mars could be habitable. But it’s a really expensive process, and a lot of materials can’t handle those temperatures, which is why NASA doesn’t bake everything. So scientists are also coming up with some other options, like using hydrogen peroxide or even gamma rays, a form of high-energy radiation, to kill stray microbes.

Ideally, these methods would kill the microbes without damaging any sensitive parts of the spacecraft or its instruments, which can be a hard balance to find. Many of these processes are still very much in development, and there are a lot of pieces we have to figure out. But we have some time.

Right now, there aren’t any planned missions that are expected to be this clean. Even NASA’s next rover, called Mars 2020, will have the same sterilization levels as Curiosity. But like it’s predecessor, it’s not allowed to go anywhere near water, so it’ll be okay.

The same is true for the InSight lander, which will go to the Red Planet later this year. It won’t have any instruments designed to search for life, so it’ll have those same requirements. Right now, sampling water on Mars just isn’t our main focus.

There are a lot of other ways we can learn about Mars’ history, like with the rock and soil samples Curiosity is taking. But as we learn more about Mars, we might eventually want to start taking those water samples. And if we do, we’ll hopefully have the right technology to check them out, without killing any aliens in the process.

Thanks for watching this episode of SciShow Space, and especially thanks to our patrons on Patreon who make it all possible! If you’d like to help us keep making episodes like this, you can go to [♪ OUTRO].