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 2.10: The upper atmosphere and the Galileo probe
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From the course by Caltech
The Science of the Solar System
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From the lesson
Unit 2: The insides of giant planets (week 1)
Meet the Instructors
Mike BrownProfessor
Planetary Astronomy
We've come up with a couple of different ways of trying to probe
the interior of Jupiter from indirect measurements of things like gravity,
things like magnetic fields.
There's one other way that you can learn about what's underneath
those clouds on Jupiter which obscure our vision of what might be there.
And, that is go there, and go under the clouds.
This was the mission of the Galileo probe.
The Galileo spacecraft went to Jupiter, orbited Jupiter for many years,
took a lot of pictures.
But, the Galileo probe was actually released from the Galileo spacecraft five
months before the spacecraft got to Jupiter.
And, it plunged directly into Jupiter's atmosphere.
It's kind of an amazing thing.
You know, the spacecraft itself used rockets to slow down to go into orbit.
It had been going quite fast on its way to Jupiter there,
going even faster because of the huge gravitational field of, of Jupiter.
The probe just went straight in.
It hit Jupiter at something like 50 kilometers a second, and
had to decelerate, had to brake with a force with 230 G,
230 times Earth's gravity, and it had to live.
And, it did. One of the reasons it lived is because it
had a massive heat shield on it to burn off as it was entering the atmosphere.
And this, this heat shield originally weighed 152 kilograms.
And, as it went through the atmosphere, burning its way in,
it lost 80 kilograms of that heat shield, just vaporizing off the sides of it,
burning off as it's going in.
When Galileo had slowed enough, the heat shield is dropped, parachute was deployed,
and the instruments started collecting information about what was there
on Jupiter.
That moment, at least in artist conception, looked something like this.
You can see the, the heat shield is glowing red hot falling away.
And, there's the probe on its nice big parachute,
suddenly going in the atmosphere.
We can actually take a look at what this thing looked like before it launched,
the actual Galileo probe itself.
It looks like some ancient World War II submarine,
experimental something or another.
And, it looks this way, because it has to withstand these
these incredible pressures as it's going down below.
It's got instruments.
We won't go into detail about all the instruments, but
all of these are different, different sensors that the probe has
that it could measure many different things as it went down.
And, the sort of time line of it's mission looks like this.
So, here it is as it's screaming into the atmosphere at at 50 kilometers a second.
Slows down precipitously, drops a little parachute fir, first.
Drops the heat shield right there.
Heat shield goes plummeting down into the interior of Jupiter.
Now, we know at least one thing that's in the interior of Jupiter.
And, the parachute deploys, and it starts to go.
So, what does it see as it goes down?
It sees wispy clouds down for a while.
Finally, a cloud layer down here at the bottom.
And, about an hour later, communications are finally lost,
as it turns out the probe eventually overheated and died.
Not surprisingly, it was designed to last about this length of time.
Right before it died, it was at a pressure of 24 bars.
Again, a bar is the surface pressure of the Earth,
so it was 24 times the atmospheric pressure of the Earth.
In the grand scheme of things, this is a tiny, tiny,
tiny bit of the interior of Jupiter.
If I drew you Jupiter, and I wanted to show you how far down the Galileo probe
went, I would draw it something like that.
Do you see that?
No, you don't see that.
It's because you could not even draw something that small.
It just was the tiniest, tiniest thin section.
And yet, one of the things that we think we know about Jupiter is that,
rather than we're not quite sure what's going on at the center,
we think that much of the outer part of it should be fairly well mixed.
So, even if you can just sample, a tiny, tiny outer layer,
you're learning a lot about the composition all the way down through.
And, what was found?
It measured the abundances of things like helium,
which we've only been assuming we knew so far.
Methane, which we see in the atmosphere, but
we don't know how much is below the clouds.
Sulphur, neon, argon, all of these things are telling you something interesting
about the formation of the planet.
And, what's been happening since then.
Krypton, Xenon, these sorts of things are great, because these are,
these are noble gases.
Noble gases really don't interact with anything.
So, measuring the abundance of the noble gases gives us a,
a very good understanding of these earliest compositions.
And, what was found?
Well, other than neon and helium,
everything seemed to be more abundant than it is in the sun.
What that means is it's, it's enriched.
If Jupiter formed out of the same nebula full of material that the Sun did,
you would expect Jupiter and the Sun to have the same composition,
unless something different happened to Jupiter.
And, it looks like something different has happened to Jupiter which has added more
Xenon, Krypton, Argon, Sulfur, Methane than it should have otherwise.
One of the things that people were most interested was water.
Water because we cannot detect it
underneath the clouds on Jupiter from telescopes.
Not because its liquid water, not because of the reasons on Mars where it has
interesting implications perhaps for for habitability on Mars.
But, in the Jupiter's case, it's the carrier of oxygen.
Oxygen is one of the most abundant atoms in the solar system, and
we'd like to know how much of it is inside of Jupiter.
And, unlike everything else, all of these things were enriched on Jupiter.
Water was much less abundant than people had originally expected.
Interestingly, water was, was less abundant than initially expected until it
got to the very bottom right where the probe was just about to be destroyed, and
then water started shooting up.
What people think is that the Galileo probe got either extremely lucky,
or unlucky depending on how you want to look at it.
And, it happened to drop into a little dry hole in the atmosphere of Jupiter.
Dropping into that little dry hole would be sort of like dropping into the Sahara
desert on the Earth.
That's just the spot you happen to land.
And, you would look around and say, wow this place is really a dry place,
not much water in the atmosphere.
Seems like a crazy coincidence, doesn't it?
But, astronomers were monitoring Jupiter from the ground before the Galileo probe
went in, and were watching a small series of these dry holes.
There are, there are always a couple of dry holes that we've known about for
a long time.
They're watching a small series of these dry holes, and
mapping where the Galileo probe would go in, and said, you know what?
It's going to land right in this dry hole, and, and it did.
So, we knew it was a dry hole.
Maybe not surprising that there wasn't as much water in there as thought, but
it'd still be nice to know how much water is really in there.
So, what did we, we learn?
Well, we now know that there are more abundant, heavier things than hydrogen and
helium spread throughout the atmosphere of Jupiter.
But, it's not enough to account for that extra mass that we need,
that we know that we need to put inside of Jupiter to make the models fit for
what it, how big it should be given its mass.
And so, it still looks like there needs to be a concentration of material
in the center that's adding the extra mass in Jupiter.
We'll now take all of these ideas together, and try to construct
a model of what we think Jupiter most looks like on the inside these days.
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