We’ve known for a while now there’s water on Mars. Lots of it, too. It’s just that all of it that we see is in the solid phase: ice. It exists at the poles, under the surface at mid-latitudes, and a teeny tiny amount in the air, too.

What about liquid water? We know the planet was wet billions of years ago, and lost all its water — and most of its atmosphere — for reasons that are still being argued over (though its magnetic field shutting down is almost certainly the root cause). There have been tantalizing hints of it under glaciers at the poles (maaaaaaaybe), but at best those would be small lakes.

However, a new study has found evidence that there could be liquid water in the mid-crust of Mars, about 11 – 20 kilometers under the surface. And not a little, either: there could be enough water there to cover the entire surface of the planet to a depth of 1 - 2 km! 

That’s a lot of water (assuming, to be very careful, that this work is correct and the water exists). How did they find it?

InSight was a probe that landed on Mars in 2018 and operated for four Earth years. It was a geography mission, equipped with a seismometer to measure marsquakes and other devices to probe the planet’s interior. The seismometer was the key instrument though: the way quakes travel through a planet can tell us a lot about the interior. Heck, it’s how we know so much about what’s going on inside Earth! For example, some kinds of waves travel through solid matter but not liquid, so pinpointing their source and being clever about where you can and can’t detect those waves can tell you how big different regions inside the Earth are. Seismology has given us a picture of a place we (at the moment at least) can never see: what lies thousands of kilometers below our feet.

The same can be done on Mars. Using InSight data, a team of scientists measured the velocities of waves traveling through the Martian interior to determine the density of the rock they passed through [link to journal paper]. They then created a variety of computer models that mimic conditions under the surface — using what’s known about density, water saturation, and other physical parameters to see how this affects the seismic waves.

The best fit they found is for a region called the midcrust, below the upper crust, when it’s saturated with water. The rock there is likely cracked and porous, and water is inside those pores. By looking at the amount of water they find, they can extrapolate the total volume, and it actually appears to be more than the volume of all the water that is thought to have existed in the planet’s ancient oceans!

That’s amazing. And it might explain what happened to all that water that used to be on the surface. Some scientists hypothesize it evaporated and escaped to space. Once the Martian magnetic field shut down, the planet’s atmosphere was exposed to the Sun’s solar wind. This essentially sandblasted the air, blowing it out into space over the course of many millions of years. Once the atmospheric pressure was low enough the oceans may have started to boil (water boils at lower temperatures as pressure decreases, and even boils at room temperature in a vacuum, for example), turning to vapor which in turn was blasted into space over time by the solar wind.

Or the water may have seeped underground, traveling through cracks and fissures until it was all gone. If this new study turns out to be correct, then that may very well be what happened — though, to be honest, I’d bet it was a combination of both methods, since that’s usually the case in situations like these. Some of the water found by InSight could have always been underground, and seeping surface water added to it. But I’m just guessing here.

This is very exciting! First off, to be clear, the water is too deep to be useful to any future explorers; we can’t even easily dig that deep on Earth yet. But if this water is there it gives us insight (yes, I know, but that’s the pun NASA used to name the mission so I kinda have to use it) into the geography and evolution of Mars. It also may help answer the question of what happened to its oceans.

This isn’t just abstract knowledge, either. We don’t really understand Earth’s magnetic field, which is absurdly complicated. The more data we have on planetary magnetism the better we can figure out our own. We’re not in any danger of Earth’s field shutting down like Mars’s did, but it would be nice to know why, for example, it flips polarity every few hundred thousand years, and determine if that’s a problem for our modern electronics-based society.

You never know what practical knowledge will come from scientific research. But don’t discount the sheer coolness of it, too. There may be liquid water on (OK, under) Mars, and gigatons of it! That, my friends, is very cool indeed.

In Issue 759 I wrote about a livestreamed interview I was about to do with Deborah Byrd from the wonderful EarthSky podcast (which used to be a segment on NPR, so it was fun to actually see her during the interview while she talked with her very familiar voice). We talked about Gaia, one of my all-time favorite space missions, and the cool science it’s doing. Black holes, binary stars, binary asteroids, galactic cannibalism and more! So much fun.

That interview is now up on their YouTube channel. However, there were some technical issues on my end so I wound up doing the interview on my phone, and the livestream video quality on my end wasn’t great. Totally my fault: the lesson here is, if you’re using a new (to you) streaming service, make sure you set it up very early in case you have problems. Irritatingly, I spent so much time trying to get my end working I didn’t have time to set up my background (I was mortified after the fact to see I had a hanger dangling off a tripod behind me the whole time) or brush up on a couple of articles so I wasn’t as prepared as I usually am. This was totally my fault, and I apologize.

Anyway, they sent me an mp4 of the interview and asked to put it up on my own YouTube channel, so here it is. The video on my end is directly from my phone and not the stream, so it looks better.

I had fun, and they gave me an open-ended invitation to come back. I’ll be happy to!

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