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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 patreon.com/scishow.

  • [♪ OUTRO]

[♪ INTRO]

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Why Mars Rovers Don't Study Water

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    林宜悉 posted on 2020/03/30
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