She ended up blowing my mind with this fact, with this phenomenon that only happens on the planet Mars, of all the planets in our solar system.

Hey, I'm Dianna, and you are probably on planet Earth watching Physics Girl.

I, too, was on planet Earth the other day when I recently dropped by UCLA to visit a really cool friend of mine.

Raquel Nuno is a planetary geologist.

And I brought her probably the most boring question you could bring to such a scientist.

Can I live on planet Mars?

Pretend this is Mars.

Not sounding good.

I don't want to live there.

RAQUEL NUNO: I don't want to live there, either.

DIANNA COWERN: Planetary geologists are creative and sneaky in finding out a lot of things, including the hospitability of Mars.

If you want to know whether Mars is going to kill you and which of its hostile traits is going to kill you first, you have to get creative.

Let's look at all the ways that Mars is a complete death trap and how we know.

Seems like a useless atmosphere is a good place to start.

So one of the biggest differences is the atmosphere of Mars.

So it's about 1% as thick as here on Earth.

So there's not much going on there.

And because there's not much atmosphere, it's hard to keep heat in.

That's actually one of the reasons why Mars is so cold.

Mars is missing a decent gas blanket.

It's like training camp on a glacier with nothing but a bed sheet.

It gets really cold.

The average surface temperature on Mars is minus 63 degrees Celsius.

Plus, with an atmosphere that's 1% the thickness of Earth's atmosphere and 95% carbon dioxide, you would run out of oxygen pretty quickly.

I think that that's very crucial for humans to live in an environment.

You need to breathe.

It'd be like trying to breathe at over 100,000 feet of elevation here on Earth.

We need an oxygen mask to assist with breathing when we get up to only 15,000 feet.

So for my Mars work, what I'm trying to understand is how the thickness of the atmosphere has changed over time.

She ended up blowing my mind with this fact, with this phenomenon that only happens on the planet Mars, of all the planets in our solar system.

Mars has this funny little thing where it tilts.

It goes through cycles where it slowly goes and tilts, and then it comes back up.

And so its orbit-- sometimes it's spinning straight up, and sometimes it's spinning sideways.

Mars is currently tilted at about 25 degrees, which is 2 degrees more than Earth.

But we have evidence that it has tilted from between 0 and 60 degrees.

And it's a chaotic cycle.

It randomly tilts.

I wanted to know why it tilts.

And so of course, I asked Raquel, and we'll get to that answer in a minute.

But first, what are the implications of this tilting?

It is a really dynamic place.

You have the poles, and you have ice sublimating, so that's going from solid to gas depending on how hot it is.

And then, when it's more straight up, it's cold.

So the atmosphere essentially collapses, and it forms back on the poles, and the water goes into the soil.

So not only does Mars tilt.

The thickness of its atmosphere changes over time as more of its poles are exposed to the sun's light.

Whoa.

Now, the atmosphere only changes by about a factor of 10.

And we're still trying to figure out exactly how much it changes.

But this is my burning question, always.

This is always the question I want to know.

How do we know?

How do scientists know that the atmosphere has become thinner and thicker over time?

You can't just send a scientist down to the surface of Mars and ask her to wave her hand around and then ask her, "How thick is the atmosphere, Marge?"

No.

And forget easily trying to figure out how thick the atmosphere was in the past.

But planetary geologists are sneaky.

This is how Raquel goes about detectiving out how thick the atmosphere was on another planet millions of years ago.

I look at small, super tiny impact craters.

So if you have a very thick atmosphere, a small rock isn't going to make it through the atmosphere.

It's just going to burn up.

But if you have a very thin atmosphere, it doesn't care.

It's just going to punch right through and create a tiny little crater at the surface.

What size crater can we make at the surface depending on how thick the atmosphere is, and then looking at the evidence that we find at the surface.

So Mars tilts because-- so a couple of reasons.

One of the reasons is that it's got Jupiter, so sometimes it pulls on it on Mars.

And the other big thing-- it doesn't have a moon like we have to stabilize its orbit.

So it can wobble because there is no moon to keep it straight up.

We're not straight up.

We're 23 degrees offset.

But yeah, we don't wobble as much as Mars does because we have this wonderful moon.

See, another reason to love the moon.

Now, with a thin atmosphere, most people think of the cold and the lack of oxygen.

But there's also no pressure.

Mars's atmosphere is 6 millibar, as compared to Earth's 1,013 millibar.

So it would just feel like being out in the vacuum of space-- not fun.

How do we know about Mars's atmosphere?

We've seen evidence for the thickness of Mars's atmosphere by looking at unusual things, like projectile rocks that have shot out of volcano eruptions, and we've observed how far away they landed.

This can tell us how much air resistance the rocks experienced when they were flying through the air, which is correlated with how thick the atmosphere was.

So we were able to learn a lot of things like this before we even landed on Mars's surface by doing flybys, like the 1965 Mariner 4 flyby.

Now we can learn a lot about Mars's atmosphere from probes that we've actually landed on the surface and some that we've crashed.

Oops.

Besides a good atmosphere, there are other missing protections on Mars too.

On Earth, we've got this weird invisible thing that goes buzz, buzz, buzz, buzz to charge particles and other harmful cosmic rays that hit Earth.

It is Earth's magnetic field.

It does really wonderful things for us, and Mars doesn't have one.

Shucks.

And then another thing that I think is really big that people don't think about-- that the sun is always blowing out massive amounts of charged particles just out through the solar system.

And we're really lucky that we have a magnetic field that deflects most of those particles.

Some still do make it to us.

But Mars doesn't have that.

So all of that ionizing radiation comes in and hits the surface, essentially sterilizing it.

That's very dangerous for life.

Mhm.

How do we know about Mars's magnetic field?

Well, now we can measure it.

But before that, there were actual rocks from Mars that landed on Earth with evidence of magnetic metals that were once aligned by a magnetic field and then frozen in place when they cooled.

So you see that evidence for an ancient magnetic field.

So we think that at some point, maybe early in its history where it still had a liquid core, a much bigger liquid core, that it did have a magnetic field, but it cooled down.

We're not sure why or how.

But it could have just been, over time, the planet cooled down and essentially turned off the magnetic field of Mars.

So Mars is smaller than the Earth, so it's cooled down a lot faster.

And we think that you need some sort of liquid component, metal, inside the core to be able to generate dynamos, which is what we call magnetic fields.

And then there's this.

The biggest volcano in the solar system is on Mars, which is amazing to think about.

So one of the things that makes the volcanoes on Mars different is because there's no plate tectonics.

Here on Earth, when the crust moves-- as the crust moves, the hotspots create a new volcano.

On Mars, that doesn't happen, so they get to be really big because of that.

Stuff comes out of the same place over and over, over millions of years, and that's how they get so big.

OK, so for habitability, we're not sure if the volcanoes are still active or not.

There could still be some sort of volcanic activity going on that could potentially erupt in the next few million years on Mars.

So if we have a base somewhere on Mars, you want to make sure that you're not near a volcano, probably, because we just don't know.

There's a lot of things that we still need to learn before I think we can determine whether or not a volcano could affect human settlement on Mars.

Interesting, right?

So then a final challenge in trying to live on Mars is finding an energy source.

Take solar.

Sometimes we look through telescopes at Mars, and we see that the entire planet is fuzzy.

Turns out, there are planet-wide dust storms.

So they can be massive.

They can actually incorporate the whole planet, what we call a global dust storm.

It's pretty nuts.

Sometimes you'll look at images from the spacecraft that are orbiting Mars, and the whole thing is just blurry because the whole planet is covered in these dust storms.

In "The Martian," that was the whole premise of the movie, was this massive dust storm caused all sorts of problems.

But in reality, it wouldn't.

And even though the wind speeds are really high, there's just not enough stuff to go around and actually cause any damage.

It'd be just like a gentle breeze in your face.

You're like, oh, this is nice.

And you know what dust isn't good for?

Solar panels trying to get sunlight.

And there's only about 40% of the amount of sunlight reaching Mars as here on Earth.

Then there's geothermal energy.

There's hardly any geological activity on Mars, because Mars is such a cold planet.

Wind is weaker for wind turbines, because there's no air, bro.

And forget fossil fuels, because we haven't discovered any evidence for any types of life on Mars, not even frogs.

So while there's still hope for crazy life forms that can survive in harsh environments like Mars, it's still a long shot for humans, until Mars rolls over and gets that thick atmosphere and warms the heck up.

Until then, enjoy your Internet videos here on Earth, and happy physics-ing.

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