Learn about the science behind the current exploration of the solar system in this free class. Use principles from physics, chemistry, biology, and geology to understand the latest from Mars, comprehend the outer solar system, ponder planets outside our solar system, and search for habitability in our neighborhood and beyond. This course is generally taught at an advanced level assuming a prior knowledge of undergraduate math and physics, but the majority of the concepts and lectures can be understood without these prerequisites. The quizzes and final exam are designed to make you think critically about the material you have learned rather than to simply make you memorize facts. The class is expected to be challenging but rewarding.
Lecture 1.25: Introduction to guest lecturers
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Do curso por Caltech
The Science of the Solar System
311 classificações
Na lição
Unit 1: Water on Mars (week 3)
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Mike BrownProfessor
Planetary Astronomy
This lecture is a little bit different, because I just want to introduce
the next two guest lecturers that we're going to have.
It's also different, because you realize a couple things,
that you can actually see my office, here.
This is where I'm sitting recording the lectures, all the time.
Usually, I have a big green screen behind me.
But this is where I am.
Another thing that you may have noticed is that I do actually own
more than one shirt.
This shirt would not be a very good shirt with the green screen.
I wear the same shirt all the time the green screen because it actually is
the best shirt that I have for the green screen.
If I did this when all the little spots would disappear,
it actually looks pretty funny.
The other thing you might have realized is I actually wear glasses.
I don't wear the glasses during the recording because again, the, it doesn't
work very well for the green screening because I'm sitting here with a big.
Window in front of me, and I sometimes get green reflected off of my glasses.
And when I try to green screen the glasses, I get little, weird sparkly
holes in my eyes and it makes me look like I'm possessed or something.
So for the rest of the time, you'll see me without glasses and with my fine,
fine blue shirt.
and you won't get to see my office behind me.
In any case, one of the really nice things about being here at Cal Tech in
the Planetary Science department is that there are people up and
down the halls who are the world's experts on so many different subjects.
Including the ones that we've been talking about.
And I can grab them as they're walking down the hall and
sit them down right here and make them record a lecture.
And so I've done that.
The next two sets of lectures are going to be from
Bethany Ehlmann who is a Professor of Planetary Science here.
And, she worked on the rover that went to that region with the hematite,
the, the opportunity that went to Meridiani Planum.
She's also done a lot of work with,
the orbiting spacecraft that take data looking at spectra.
We've talked about spectra some,
we've showed the spectrum of hematite, but since that time there has been much more
detailed spectroscopy to learn about the detailed minerology of what's.
Going on, in different regions on Mars.
And she's going to tell you all about that.
And use that to spin an entire story of the history of Mars.
After she's done with that, we're going to drag in John Grotzinger,
John Grotzinger was the chief scientist on the Curiosity Rover,
that one that's on Mars right this very minute.
And he's primarily a geologist, he looks at the.
The land forms on Mars and
tries to construct stories of what might be going on there.
It's interesting that you will, if you listen carefully,
you'll notice that Bethany Ehlmann whose mostly a mineralogist,
thinking about certain, the chemistry, and John Grotzinger, whose mostly a geologist,
thinking more about the landforms.
They actually come to some different conclusions about the history of Mars and
what might have been going on over the past four and a half billion years.
The story, the overall story is the same but the details are different.
See if you can pick out where they don't agree with each other.
And after they're all done, we'll come back, summarize everything that we
think we have learned about Mars, and how we're going to answer these.
Final questions that we'll still have, particularly after we see
the two different interpretations of what might have been going on.
Oh, hey, it's me again.
Before you watch the next set of lectures,
I just wanted to have a quick discussion about some terminology that's going to be
used, that we haven't used in class before.
You'll hear both Bethany Ehlmann and John Grotzinger use the term oxidizing or
reducing.
To describe environments, atmospheres, or subsurface environments.
These are words that are actually from a long time ago when
iron ore was first being smelted to form iron.
To form iron you take the iron, you put it inside of a kiln,
you heat it up very hot, and you reduce the amount of oxygen in the environment.
And the oxygen that's in the iron ore comes out of the iron.
It is reduced from its iron.
It's reduced in mass from the iron ore to turn into the iron.
That was called a reducing reaction because it was reduced in, in,
in mass and oxygen was released.
Oxidizing, well, it's sort of the opposite.
If you take iron.
And you put it in an, a oxygen rich environment.
What happens?
We know it, it gets rusty if you have a little water in there.
You get an oxidized iron.
Although the terminology comes from a long time ago, it's still the same terminology
that's used now to generally describe different types of chemical reactions.
We're not going to go into detail about the types of chemical reactions that
are either oxidizing reactions or reducing reactions.
But I just want you to, in your mind, when these words are used,
oxidizing or reducing, think of it as either an oxygen rich environment,
oxidizing or an oxygen poor environment, reducing.
It's not strictly true.
You can have oxidizing environments that have no oxygen in them at all.
But we're not going to worry about that for now.
On the Earth, well, as you know,
the, the surface of the Earth is generally an oxidizing environment.
That's a good thing.
We sort of like oxidizing.
Where do you find a reduced environment?
Anywhere that is anoxic, anywhere that oxygen doesn't exist.
You can get these in, in marshes, underneath the waters,
in very stagnant water where there's no oxygen flowing through the water.
These sort of anoxic environments are ones that certain types of microbes
really like quite a bit.
You'll hear a couple different statements about about oxidizing and
reducing environments.
One of them that you'll hear.
Is that a reducing environment is favorable for
the development of life, and so finding a reducing environment is a good thing.
Sounds a little bit weird given that we like oxygen so much, but
the Earth didn't always have oxygen in it's environment, as we'll talk about.
Later when we talk about the development of life on Earth,
the first life that developed on Earth developed in reducing conditions.
And it's thought that those reducing conditions are a lot easier for
early life to develop.
Now that life eventually lead to oxygen being created and
now we have a nice oxidizing environment.
Nice to us.
Poison to all those other microbes.
Another thing that you'll hear is that a reducing environment is good,
not because it's better for life.
But because it's better for preservation of the, the remnants of life.
If life existed somewhere in a surface.
Better to have it existed in a reducing environment so
we can still see the signatures.
What does that mean?
Well you, you sort of have heard this sort of terminology before.
You know that oxidants in your bloodstream are considered bad, and
you're supposed to take antioxidants to get rid of the oxidants that are in there.
Antioxidants are just reducing agents.
Oxidants in your bloodstream.
What do they do? Well they attack the organic molecules in
your body and they destroy them.
Oxidizing agents in the Martian atmosphere or Martian environment will do the same
thing to any organic material that you would have liked to have persevered.
On the Earth, what do we do to prevent oxidation of our organic material?
I think the answer is we're supposed to eat blueberries or something.
Or, what we do?
We, we mummify.
What does mummify do?
Mummify puts you in an anoxic environment.
Burying things inside of swamps probably also a good thing.
On Mars, we keep an eye out for these reducing environments.
The current surface of Mars, you might think to yourself, well, it doesn't have
oxygen, so it's probably reducing environment, but it's actually not true.
This is where some of the complication gets in.
The actual surface, the chemical reactions that are taking place at the surface due
to radiation coming in, and due to the the surface composition, is actually
oxidizing, so any sort of organics that were sitting out exposed on the surface
right now would be quickly eaten up and we would have no idea that they were there.
So as we go through the next couple of lectures and
we talk about different environments on Mars, keep these thought in mind about
reducing environments, about oxidizing environments and
you'll have a much better understanding in general what's being discussed.
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