Planetary Profile: Mad Mars

The 13^th anniversary of the Curiosity rover’s landing on Mars seems like a good opportunity to continue my weird solar system series (here’s the posts for Mercury, Venus, and Earth, if you’re interested!). As the planet we’ve visited the most, you might think that Mars has the least amount of mystery to it (well, for planets that aren’t Earth anyway).

But the Red Planet has a way of confuddling us like no other world. Every time we learn something new it just raises twelve new questions. So let’s get to know our ruddy neighbor and find out some of the ways Mars definitely qualifies as weird!

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Rose-Colored Everything

Let’s start with Mars’ distinctive coloring. It is, after all, famously the Red Planet. That’s because the dang thing is rusty. The color comes from iron oxide, aka rust, in the Martian soil. Mars’ bedrock is rich in iron. Combine iron with oxygen and you get rust.

But it turns out there’s rust and then there’s rust and they’re not all the same. Figuring out just what kind of rust Mars has can help us a lot in figuring out its history. For a long time we thought Martian rust was best described as hematite which, importantly, does not need water to form (we know there was definitely a watery period of Mars’ past—more on that later!).

If that was the case it actually means Mars went rusty after its early wet period was well over. That would mean our Red Planet actually spent a big chunk of its history as the Gray Planet. A more recent study, however, suggests something very different. It says that a better match for Mars’ rust is ferrihydrite, which needs water to form. That would mean Mars went all red when it was still damp, and it’s had its distinctive coloration for most of its existence.

So our Red Planet started out as the Gray Planet before it rusted. That’s weird.

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Warmer and Wetter

Let’s talk about Mars’ past a bit. We know it used to be warm enough for liquid water to form because there is a ton of evidence for flowing water on its surface that our spacecraft have tracked down. Riverbeds and deltas, silica deposits, sedimentary rock laid down in lakes…we’ve found it all. Mars definitely had liquid water on it once upon a time.

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Which means it had to be warmer, given that Mars’ average temperature these days is around -80F (-62C). It’s cold. It does, occasionally, reach more pleasant temperatures around the equator on a summer’s day, but apart from those infrequent circumstances, Mars is frigid. So how could it have been warmer in the past? Easy, it used to be a much livelier planet.

When Mars first formed, it had a moving liquid iron core, much like Earth’s. Earth’s core creates its magnetic field and so did that of early Mars. These sizzling innards also drove extensive volcanism on the surface. Between the two of these, Mars once had a lot more atmosphere.

The volcanoes belched out gases from Mars’ interior, augmenting whatever atmosphere Mars originally formed with. Volcanic gases can make good greenhouse gases, trapping heat from the Sun, so Mars essentially once had a very nice gas blanket around it. And it had a magnetic field to protect that blanket from the forces of the solar wind streaming off the Sun, which can strip an atmosphere from a planet that’s close enough. The magnetic field would have directed most of the force of the solar wind around Mars, like how Earth’s works today.

So as long as Mars had this highly active interior, it was constantly adding to its atmosphere and protecting it at the same time. All good, right? (Please, you can guess where this is going.)

It’s Dead, Jim

Yup, that interior did not remain highly active. For…reasons?? Nobody is quite certain why, although there are many theories, but the movement of liquid iron in the core that was generating the Martian magnetic field ceased. The solar wind moved in, stripping away atmosphere. The volcanos may have helped keep pace at first, but with the chilling out of the planetary interior major volcanic activity on Mars is thought to have ceased by around 3 billion years ago.

Today Mars’ atmosphere is about 1% as thick as Earth’s. Despite most of that being a notorious greenhouse gas, carbon dioxide, Mars is absolute rubbish at holding in heat from the Sun. Its blanket is gone, leaving the frigid world we see today where the air is so thin that even though we think Mars can generate nearly hurricane-force winds, the force from them would barely be enough to fly a kite properly.

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(If you’re wondering about that opening scene in “The Martian” where a catastrophic Martian windstorm tears pieces off an astronaut base, that’s a little creative storytelling. Andy Weir, the author, fully acknowledges that such a storm would feel like a light breeze in real life, but he didn’t know how else to get his story going, so he made it up.)

I quoted Star Trek to say Mars is dead, so I’ll quote Monty Python to say that actually it’s possible that Mars is “not dead yet!”. The core movement generating the magnetic field stopped, but the core didn’t go solid. NASA’s InSight lander measured something like 450 Marsquakes during its first year on the Red Planet. There’s definitely still stuff moving around down there, and also it sure looks like there’s a giant magma plume rising up beneath Elysium Planitia. If it reaches the surface Mars may yet experience a new major period of volcanism!

Highs and Lows

That’s a whole bunch of stuff about Mars that is not only weird but also mysterious enough that a whole lot of really smart people are spending their careers trying to figure out. Let’s look at a few simpler ways in which Mars sticks out. For one thing, its topography is insane.

Have you ever seen the MOLA images of Mars, with rainbow colors used to represent the height of the surface features? If so, you know that Mars is a world of highs and lows. Most of northern Mars is colored blue for lowlands, while most of southern Mars is red for highlands, except for one gigantic blue hole. Then there are at least four points that are so high they’re white rather than red and a great big slice of low not far from those white points in the midst of the highlands.

The weird dichotomy in altitude between Mars’ northern and southern hemispheres is a major Martian mystery. There is one theory that suggests that the northern lowlands of Mars may actually represent the largest impact site in the solar system, which is crazy and awesome and would have probably come close to tearing the planet apart.

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Then there’s that giant hole in the southern highlands. That’s Hella Planitia, also sometimes called Hellas Basin, and that is most definitely a giant whopping impact site. It’s 1,400 miles (2,300 km) across and somewhere around 30,000 ft (9,000 m) deep. It’s huge. I tried to find speculation on how big an impactor it would take to form something like this and couldn’t even find it, but it would have been a Bad Day to be on Mars.

That slice of low in the midst of the upper highlands is Valles Marineris, aka Mariner Valley. It’s also big, just in a long, skinny, deep way. It’s a canyon, but that’s like saying the Pacific Ocean is a puddle. Valles Marineris is the biggest canyon in the solar system, as long as the continental US is wide, and gets over 4 miles (7 km) deep. So. You know. Just a canyon.

What’s more, we think Valles Marineris might have formed in a single traumatic day when pressure below the crust reached a breaking point and epically split the ground open. That pressure probably would have come from some of those four white points in the MOLA data. Three of them are in a row, and represent one of the craziest landforms on Mars, Tharsis Plateau.

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Tharsis is a region where Mars bulges outward dramatically and is topped by three enormous volcanos, Arsia, Pavonis, and Ascraeus Mons. A hotspot under the crust in the old volcanic days probably raised the plateau and kept all three volcanoes good and busy. Just a little ways off is the Big Grandaddy of Them All, one of the most famous landforms in the whole solar system: Olympus Mons.

This ancient shield volcano rises to a height of 13 miles (21 km) above the surrounding plains. If you put in on Earth it could cover France. It barely misses out on being the tallest mountain in the solar system, edged out by Rheasilvia on Vesta (which I’ll get to when I tackle the weird asteroid belt!). Mars may be smaller than Earth (only a little more than half its size) but that doesn’t mean it doesn’t go to ridiculous extremes!

Wrapping Up

This is, of course, only a taste of why Mars is weird. I could have talked about the periodic dust storms that cover the whole planet. Or the fact that clouds of methane play hide and seek with our spacecraft. Or its two wee dinky moons which may be captured asteroids or could be chunks of Mars blasted off into space by impacts. Or the fact that we think it’s entirely possible this planet once supported life (though, to be clear, we have no definitive evidence for that. Yet).

But I think I’ll wrap up with my favorite fact about Mars: it is the only planet in our solar system that is entirely inhabited by robots! With the big rovers Curiosity and Perseverance powered by nuclear energy sources that can keep them going for years and years, this might just remain true right up until human boots set themselves into the red dust of Mars for the first time. We’ll just have to wait and see!

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