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Our Past and Our Future?
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Do curso por Princeton University
Imagining Other Earths
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Mars
Mars may be the other planet in the Solar System that hosts life. This lecture introduces the basic properties of Mars, Mars’ atmosphere and its seasons. We discuss Martian exploration, the search for water and methane on Mars and potential signature of life. Seasons.
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David SpergelCharles Young Professor of Astronomy on the Class of 1897 Foundation and Chair
Department of Astrophysics
Mars may have been an important part of our past,
and intriguingly, could be an important part of our future.
We'll come back to this topic when we talk more about the origin of life.
But many scientists speculate that our ancestors
may have been Martian. Early Mars, was actually a more hospitable
place for life than early Earth.
It probably had liquid water first, was once warmer, and
when we look at places where life could've originated, and we'll talk a lot more
about this towards the end of the course and we start talking about
the biochemistry of life and what are the ingredients need for its origin.
Mars could have been a place where life could have started.
And since Mars to Earth transfers pretty efficient with these meteorites
as I've mentioned already, we find martian meteorites on the Earth's surface.
It's possible, life started there.
And if so, it'd be very intriguing to find out more about this.
To really go back and trace our origins.
Mars
is an interesting place to get to. And maybe an important part of our future.
And before I talk about Mars exploration,
I want to talk a little bit about one of
the things that makes it so difficult to
get to Mars, and so difficult to explore space.
In order to understand that, we have to think about how rockets work.
The way rockets work, is they send stuff out the back,
momentum comes out the back, and, this goes forward.
Newton's laws say that the momentum that goes out the
back, and the fuel here times the velocity of the fuel.
Balances the mass that goes forward, and the velocity out.
And in order to move something, very fast this way,
you've gotta send a lot of stuff out the back.
This is why when you look at a rocket, and here's a model, of,
NASA's next new big rocket, the space launch system, you
have, a lot of rocket and exhaust, and
relatively little material sent out into space.
This balance could be understood, by the fact that it takes a
lot of momentum going this way, to move a rocket fast this way.
If you want
V here to be big, keep these in balance.
This mass that goes out, has to be much larger than this mass here.
We could quantify this, by solving the balance and looking at the acceleration.
When we do that we get what's called the ideal rocket equation.
Which relates the mass and fuel you'll need, to the mass and payload.
And the fuel mass,
go through this, equals the payload mass,
times an exponential factor of the ratio of
the change in velocity you need to
reach your target, divided by the exhaust velocity.
In order to get to Mars, the change in velocity you
need from the Earth's surface, is about 23 kilometers a second.
To get to Mars and land on its surface. When we look at
the effective exhaust velocity, a material coming out of
modern rockets, we're looking at exhaust velocities in this range.
So we're looking at a factor of 6 or 7 here.
So, the fuel mass is going to be exponential, e to the
6 or e to the 7 times larger, than the payload mass.
So we're going to need a very big rocket, to send a payload
to the Martian surface.
What makes this even more challenging, is if you want to think about the
problem of getting something from Earth to Mars, and then bringing it back.
So right now, we're able to, you know, send things like the curiosity rover,
which is pretty big, from the Earth's surface to Mars and land it there.
But the curiosity rover doesn't come with
a rocket. Imagine you want to go back, to Earth.
You have to land a rocket on the martian surface, and you've got to have this
little piece here, now be big enough, that its payload, it can carry its own payload.
So you've gotta have a rocket carrying another rocket, that carries a payload.
That makes it very expensive
to get to Mars, and then come back from Mars.
What we think of as the next step in
this process, is not sending humans to Mars and back.
But first sending material from the Martian surface back, and the plan
as of a few years ago, was to have a program of Mars sample returned.
Where a joint European, U.S.
effort, would send a mission in
2018, that would begin the process of Mars sample return,
by landing a rocket, landing a rover that would collect samples.
And then begin a project of bringing those samples back to the Earth's surface.
Because of budgetary limitations,
the next Mars mission is now Mars 2020. But 2020 is coming,
and NASA has just announced plans to develop this Mars 2020 mission.
And that will cache samples, it will go along the martian surface.
Identifying interesting rocks and many of us hope,
lead to a future mission.
Mars 2020 will not be capable of bringing material
back, but the hope is it will, collect material,
after that material is collected, a future mission will
take those samples and return them back to Earth.
Once we've done that step, we're able to
bring a rocket, have a rocket that can pick
things up and bring it back to Earth.
The next step, maybe thinking about humans.
And how do we send humans to Mars?
There's, broadly speaking, 2 ways of thinking about sending humans to Mars.
One way is to imagine a mission, that goes
to Mars, lands a rocket on Mars, that rocket then
takes the humans back off the Martian surface, into Martian
orbit, where they then return, and this will again, require
a vehicle that has fuel with it, so they
can change orbit, and go from Martian orbit to Earth's orbit.
That is an extremely ambitious mission.
What a lot of us have recognized, many people have thought about this problem.
It's much easier
to offer a one-way ticket to Mars. And to think about the way that
we will explore Mars, is we will first send, say supplies to the Martian surface.
You'd have a program where over say 2, 4 years before you ever think about
sending humans to Mars, you would send material to Mars, so when the humans land,
there would be places for them to live, there'd be food for them.
Once you've established camp on Mars, you then send the people.
Now, one of the interesting things to thing about how this works, is, you may
end up sending people, but tell them when
they go, there's no guarantee they're coming back.
That they may go to Mars, and live
out the rest of their lives there.
That we would continue to send food supply there, remember it's
a lot easier to get stuff to Mars, than get things back.
But that we might not be able to send them a rocket to come back.
When people think about this, they speculate that perhaps we could
develop a system, so that the astronauts can use material on the Martian
surface, to extract water, extract some of the
things they need to live, and perhaps to
extract some of the materials, that they could
be used for the rocket fuel for their return.
There have been calls for applications for people who
want one way trips to Mars, and many people volunteer.
I've discussed this in my freshman classes over the years.
And I always ask for a show of hands, for
who's willing to take a one way trip to Mars.
I'm always surprised to see that about half of my students, are willing
to take a one way trip to Mars and live there.
There are a bunch of reasons why we might want to go to Mars.
And I think many of us have different answers.
One reason is, scientific.
We can learn a lot about Mars from the rovers, but humans on Mars would
be able to carry out types of
scientific investigation, that can't be done by rovers.
However, scientific arguments alone are probably
not going to motivate a Martian mission.
A Martian mission would be very expensive and we could probably
get more science per dollar, by sending future rovers and orbiters.
What is likely to motivate Martian exploration, are other considerations.
Considerations like sending humans out in space,
might be an important step in the development of the human race.
Personally, I'm intrigued by the possibility, that
it gives us a chance to think about who is we, and how we want to explore Mars.
And some of this is this exploration done
by the United States?
By the United States and some of it's traditional
partners.
Europe and Japan, have often worked together
with the United States in space missions.
The Space Station, one of, I think, it's greatest successes, is not the science
done there, nor the tremendous engineering developments
associated with the station.
But the fact that the United States and
many partners, including Russia, who plays a vital
role in the space station, cooperated together,
to send people into space and to populate the space station.
I think the most valuable thing that Martian exploration might do,
is to have we equal humanity.
That we recognize Martian exploration, as something
that we do as a species.
And that this is something that many
nations would contribute to, in different ways.
In making the investments and developing the technologies needed, to send people to
the Martian surface, and establish a Martian
colony, that is not national, but transnational.
That's my own prejudice on why we should go, and my own
prejudice on how we should get there is, just because
it's cheaper and easier, send people one way, let them stay.
See what develops.
I'd like you to think about this question of,
should we make the investment of, needed to explore Mars?
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