Are we alone? This course introduces core concepts in astronomy, biology, and planetary science that enable the student to speculate scientifically about this profound question and invent their own solar systems. All the features of this course are available for free. It does not offer a certificate upon completion.
Mars and Water
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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
One of the many fascinating features of Mars is Mars has water.
Water, as I'll discuss when we talk more about biology, seems to be vital for life.
It's certainly vital for life on our planet.
And one of the very important discoveries of the last decade or so,
for Mars missions has been the ubiquity of water and the fact that water
exists in Mars today.
It's flowing on Mars today, and as we'll discuss, in the
past, there may have been standing bodies of liquid water on Mars.
When we look at water on Mars, water takes several different forms.
Will often be thinking about whether the waters
existing, within Mars in the form of brines.
Brines are very salty mixtures of water.
They can water
without salt of course freezes at zero
degrees centigrade, but as you add more and
more salts to it, it can stay in a liquid form at lower and lower temperatures.
You can think of, this is adding salt is a lot
like, it actually is really the same thing as adding anti-freeze.
What anti-freeze does is stop the water from freezing.
And we suspect that there maybe subsurface
liquid water on Mars, we actually have pretty
good evidence for this now and a lot of that may
be in the form of these brines that are filled with antifreeze.
We think that early Mars was much wetter.
And we see evidence for, what looks like standing water on early Mars.
And there's a big debate in the Martian scientific
community whether or not the early Mars was cold
and wet or perhaps even a warm, wet planet
perhaps in some ways a bit like Earth today.
Martian history was really divided into three periods.
Its earliest period during its first nearly billion years.
The earliest part of it, like on Earth, was a period of very heavy bombardment
as the solar system was assembled from planetesimals,
small units of smaller than planets that
rained down on the Martian and Earth surface.
This heavy bombardment period ended about 7 - 800
million years after the formation of the solar system.
During this early period there seems to be pretty clear evidence for liquid water.
That was then followed by another period of about half
a billion years, during which there was very active volcanism and
we see extensive lava plains on the martian surface
and these lava plains built up during this period here.
Then we enter our more modern period, this, of the last three billion years.
This modern period, we don't seem to have, much evidence for this
very heavy rate of volcanism, nor for the presence of standing water.
Mars became, after a billion and a half
years or so, a relatively quiet, dry planet.
What we'll talk about on, with Mars with its
water, is the possibility, that deep underground, there could be
life in Mars.
One of the people we'll be talking to, through this course is Tullis Onstott.
T.C. Onstott's a colleague of mine in geosciences.
What T.C. does is he goes down into
underground mines and studies some of the bacteria that
uses, as its energy source, free hydrogen with radioactivity,
rather than solar energy, as the fundamental energy source.
We see these same kinds of bacteria, not just
in these underground mines but also in undersea vents.
And, the presence of these kinds of bacteria, has led to
the speculation that life forms like this, could exist in subsurface Mars.
And we'll talk more about this when we return
to the subject of life later on in the
course, and start speculating about the range of life
forms that could exist through our solar system and beyond.
So, let's get back to talking about water.
When you look at observations of the Martian surface, and again, let
me encourage you to explore Mars yourself and look for these features.
You will see things that look like river valleys and regions
where what looks like a river flows into an alluvial plane.
This looks so different in some ways from the Nile River or some other
river flowing into an ocean, or perhaps flowing into what once was a lake.
We see these channels, we see these aprons.
As you look across the martian surface there are a number
or regions that look like they were produced by flowing water.
And lets zoom in on some of these regions
and you know this doesn't look so different from
when you go to the beach and you see
stream flowing in, and what patterns those streams make.
And geologist
study these features in detail, and many have
inferred the presence of flowing water from these regions.
The water continues to flow today.
This is a fascinating picture of the martian surface here.
Some observations in August of 1999 of a crater wall.
And you can see, let's focus on this region here,
that there's nothing here. This is a scale of about 300 meters.
Now, when the orbiter returned and took an image
about six years later there was this new deposit here.
So something had changed. And this looks a lot like what will happen
if an underground stream reached the surface and deposited material here.
So we find evidence that there's flowing water today on Mars.
At least some surface water that comes out and leads to temporary deposits.
And here we are, zoomed out on this feature.
And you can really see this remarkable feature, which
does look like there's evidence for flowing water on Mars.
We've learned more about the Martian's surface from the Mars rovers.
Here's a image
of what a rover sees.
And as they've explored, they find things like silica.
Silica is a product of standing water.
In order to produce a rock like this, you really want to have liquid
water, that sits there for a long time. It's just not something that just
temporarily, bubbles up to the surface. And here,
when the rover, goes in and scoops the surface.
You don't have to go very far below the surface before you find more water.
And one of the other ways we find water is by monitoring it from space.
And we can actually use cosmic rays.
Cosmic rays are protons, mostly, but also other nuclei that have been accelerated by
supernova explosions, and by their shock waves to very high energies.
These galactic cosmic rays are moving at speeds close to the speed of light.
So they carry a great deal of energy.
These cosmic rays are raining down on us in the room right now.
They're actually one of the significant
sources of radiation and mutation on Earth.
They are
partially to blame for some of the cancers on Earth.
Actually, they're completely to blame for some of
the cancers, because they're a source of mutation.
And what happens on Mars is, the cosmic rays come in, they interact
below the Martian surface, and produce neutrons that come off,
and these neutrons interact with materials in the surface and
produce gamma rays. The orbiters then detect these gamma
rays, and because the type of gamma ray that's produced
depends on what the neutrons interact with these gamma
rays can tell us about the composition of sub-surface Mars.
And here's some data showing maps of Mars and the the distribution of
water from the Mars orbiters.
And what we find is one to two meters
below the martian surface, there is significant amount of water.
And I've already touched on the intriguing possibility that
there may be methane on Mars produced from sub-surface life.
Our current best data from Curiosity suggests that this methane might
might not be there, as Curiosity doesn't see it.
But many people remained intrigued by it.
Curiosity is our current Martian explorer.
Let me again encourage you to after this
lecture to go look at the link that describes
Curiosity's landing on Mars, and also go to Curiosity
web page which has a lot of interesting information
about some of its most recent discoveries.
The curiosity rover is a real upgrade from the earlier Mars rover.
It's much larger and has a number of powerful instruments.
Here's a schematic of it.
It has a robotic arm that lets it go out and reach samples.
It has a rock crusher that lets it look at composition.
An X-ray spectrometer that will let it study
the properties of the materials it's, on the surface.
A laser, that will let it vaporize soils.
And it's really going to be able
to characterize the Martian environment in detail.
And it's currently zooming around the Martian surface.
Curiosity has already provided some really intriguing results.
It recently reported that, when you look at your, the typical sample of Martian
soil, taken it's first early samples these samples contain 2% water.
So there's a lot of water embedded in Mars' surface layer.
It found strong evidence that early Mars had standing water.
This is arguing for a planet that was once, not just having
underground streams, but having real lakes that persisted for a long time.
The geology's consistent with the kind of rocks that form in standing water.
And it also helped confirm the martian evidence of earth meteorites.
It was able to get some of the distinctive chemical signatures and isotopic
signatures of the Martian rocks, so that when we find them on Earth, we
know that these meteorites are material that was once on the Martian surface,
and transferred from Mars to Earth in the form of a meteorite.
So we're already starting to learn some really interesting things.
Curiosity rover and
the the future Mars missions are aiming
at addressing a number of fundamental questions that
we have about Mars, we'd like to understand
how Mars has varied through time and why.
As I've mentioned earlier, Mars in its past was once wetter.
It had active volcanism. It had and early magnetic field.
Big question is, did Mars once host life and does it host life today?
We'd like to understand martian climate and understand its evolution.
Mars' climate is evolving both on long time scales
as the composition of this atmosphere changes, and on shorter time scales.
The Martian orbit is changing on the time scale of millions and tens of millions
of years.
And that leads to long term variation to Martian climate.
We'd like to understand Mars's interior what sets
it's properties and how has it evolved in time.
Mars is a much smaller planet than Earth.
That means its interior can cool much
more, has undergone, as a result, significant evolution.
She there's a lot we'd like to understand
about Mars's interior geology.
And we will look at the Martian surface, the Martian surface is very diverse.
And as you explore the diverse geology, you'll find, as you go to
that mars.google site you'll see that we see lots of intriguing features.
And in fact, the thing I'd like you to do next when you exit
here, is to look at that website
and to answer some questions about Martian surface.
So why don't you do that, and then we'll come back and talk
some more.
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