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Mars sample return has been a high priority for the scientific community for a long time. The
dark comedy sort of joke has always been that Mars sample return is 10 to 15 years away,
no matter what year it is. So here we are, we actually have a mission, it's built, it's
sitting at the Cape, it's getting ready to be launched. That will be the first stage
in returning samples from Mars. It's just huge. It's an Apollo 11 type mission, because
of the unique properties of Mars, because of the whole question of, "Has life ever existed
anywhere else?" All of those things are all wrapped up into this particular mission.
The question of whether any environments on Mars were habitable or are habitable today is really
what drives things. There's this remarkable global climatic change that occurred right
around three and a half to four billion years ago on Mars that took it from a planet that
probably was habitable  to something that's desolate and dry and irradiated at the surface
with a thin atmosphere now. The really interesting thing is to do this comparative planetary
geology to say, well, why did the Earth evolve the way it did with abundant life? And why
did Mars evolve the way it did in its own unique way? To find answers to these questions,
scientists use orbiters, landers, rovers, and recovered Martian rocks that can survive
the trip down to Earth. I'm sitting in the University of Alberta, Meteorite Curation
Facility. It's a lab that I built and designed, where we have a clean room, which you can
see over my shoulder here. It's the sort of glassed in area and the rock cabinets in there
have about 1800 specimens of different meteorites from around the world. The Martian meteorites
are a unique set of rocks that have been blasted off the surface of Mars, naturally. There's
140 or more meteorites and over 80% of them are basically lava flows that float out on
the surface of Mars in the last few hundred million years. Now Mars is four and a half
billion years old. So there's a whole history there that's missing because of a bias in
the way that these samples are delivered to us. And that's what makes this upcoming launch
an ambitious new chapter in Mars exploration. It's the first step in a series of proposed missions
over the span of a decade to bring samples back, with all of the source material. The
idea is to go to a place where the rocks are of that age of at least three and a half billion
years, so that we can probe those for evidence for ancient life. The landing site is Jezero
Crater. It's a remarkable 45 kilometer diameter crater that was filled with water, had a river
flowing into it and a river flowing out of it in a key timeframe in Mars' history. There
are mineral signatures that have been detected from orbit, including carbonate. And carbonate
is a mineral that life can sometimes use, as part of producing, say a hard shell. Those
rocks are beautifully preserved. You can see them from orbit. And that's the real reason
why this was chosen.
The whole idea is to get a cache of samples that are so compelling
to the scientific community, that the space agencies could do nothing less than spend
the money to basically bring everything back. That's a tall order for this new rover,
but luckily, NASA's engineering teams are experts at building capable robot geologists. Mars
2020, the advancement is adding the sample caching system. We have a bit carousel that
holds all of our various bits or tools that we have for working on Mars. We have a five
degree of freedom robotic arm that's on the outside of the rover that allows us to not
only dock for tool exchange but also for placing some of the science instruments. The drill
is able to not only be the jackhammer where it actually takes out the sample from the
rock, but it's also able to do very delicate tool drop-offs. It's a very complex system.
This is the inside of Building 248 on the NASA JPL campus. It's where Eric and his
team put the sample caching system to the test. So in order to really make sure that
the system's going to work, we always try to emulate the environment that we're going
to work in. We have a Geo analog team that allows us to collect rocks something approximately
close to what we might see on Mars. We created this unique test setup, where we're able
to be in a thermal vacuum chamber, that allows us to get down to the Mars pressure. We have
to make sure that we've learned how to get the teeth of the drill just right to get a
sample. Our testing over time has been an iterative process that helped us design a
better, more reliable sampling system.
The targeted launch window for this rover is July
through Aug 2020, with a landing date of February 2021. After it survives the trip to Mars
and sticks the perilous landing, the rover will take some time to get situated. There's
usually a commissioning period It's been a long ride and everything's just kind of unfolding
and getting itself ready. At that point, they want to start taking advantage of where
they're at. Where did we land? What can we see? The main approach  is to look at a
region of interest do a walkabout. We have cameras that are able to get the mineral signatures
of rocks. We have the super cam, which is essentially a laser that can zap the rocks a few meters
away, and tell you what they're made of, which I just love that. It's fantastic. That one
has a microphone attached to it now too. So we'll be able to hear the rocks getting zapped
from a distance which is pretty awesome. There is going to have to be a certain balance between
the desire to completely explore and then decide from there what samples you're going
to get. We're trying to keep everything within a one Martian year, which is about two years
Earth time to get all the samples collected. There is a pace that the science and operations
team are working to. There's 43 tubes 37 is the number that we expect to bring back. Our
job is to put a sample in every tube and the scientists will have to choose which ones
to leave behind. So we hope to give them a really tough decision. I'm really looking
forward to those conversations when we're doing the mission operations. We've got a
bit of a hint of it a couple of months ago, when we were all working remotely on a simulated
rover mission, where the folks from NASA JPL went out to the Nevada desert and set up a
bunch of instruments, and made it look like the Rover was there. And the discussions
about what to sample were absolutely fascinating. Something that would be really compelling
would be like a mudstone, like a really fine grain rock that was deposited within the delta,
that has lots of organic matter in it. Another really compelling thing, of course, would
be these carbonate rocks. So this whole discussion about, would you, should you collect that
particular sample, or should you explore more. After some careful decisions, the rover will start
caching. Once we've taken a rock from the ground and it's in the tube, the sample handling
arm, inside the belly of the rover will actually go and pull the sample out and start to process
it. The autonomy that's built into the system is fairly incredible there's a lot of closed
loop motor control activities. Once we actually expose a sterile tube to the Martian atmosphere,
we have a five hour timeline to actually get it sealed. Contamination is a critical part
of our mission. We don't want to take any organics with us. This is something that
feels like a Sci Fi movie but it's reality. The plan is to drop off the samples in bunches
around Mars where a future mission would land and use a fetch rover to go and pick them
up. They'll be installed into a Mars ascent vehicle, which will then launch off of Mars
into a Martian orbit where another mission would come rendezvous and pick up the sample. And
then that orbiter would then turn back and head back towards Earth. The current plans
are for the samples to be returned to Earth in 2031. There's a small, but non zero chance
that there is extant life that could come back with the samples. And so that's where
the other part of Mars sample return is really important, which is the sample receiving facility.
And then the design of that is going to be next level kind of stuff though, because the
same time that we're trying to keep whatever is in the samples from getting out into the
Earth environment, we're also trying to keep the Earth environment from getting into the
samples. I'm one of 10 people selected as a Return Sample scientist, through a NASA
call. These are all people, like myself, who have experience in the lab with samples of
meteorites. You know, age 13, I think, I said I want to be there when the samples come
back and it's a dream come true to really be involved as a return sample scientist,
as someone who is an expert in what you do with the samples when they come back.
I sure hope I'll be able to see them. I'm going to have my favorites. They are going to be curated
under the best possible conditions and preserved indefinitely for generations to come. Each
one of those will be scrutinized like you wouldn't believe, the way that all the Apollo
samples have been scrutinized for 50 or more years, now with the added bonus, of course,
that we're actually going to an environment that could potentially have been habitable.
To hopefully answer the big question: was there life on Mars? I don't really have a
good answer for that but another way to look at that question is to say, well, if we don't
find life that's a significant step toward understanding what life is all about. And
how unique it is, for example, for the Earth. On the flip side, if we do find evidence for
ancient microbial life it just opens that door to life being incredibly abundant throughout
the whole universe on these almost infinite number of planets that are being discovered
in our galaxy and beyond.
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美國宇航局雄心勃勃的將火星樣本帶到地球的任務。 (NASA’s Ambitious Mission to Bring Martian Samples to Earth)

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Summer 發佈於 2020 年 9 月 10 日
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