Lunar Flashlight trouble, Immense Martian basin has a surprising origin

Subscribers have a huge impact

News Cues

I choose a few to imbue clued views

Back in BAN #487 I wrote about the Lunar Flashlight space mission, which will orbit the Moon and map out ice in dark craters at the south pole using infrared lasers to illuminate them. It launched in December, and is taking a complicated trajectory using very little fuel to get into its prescribed orbit.

It’s a small satellite — literally called SmallSats — designed to be inexpensive and use very little consumables during flight. One of the secondary goals of the mission is to test out a new “green” fuel, which is safer to store and use than the usual hydrazine. The fuel has been used in a couple of missions before but never to put something into lunar orbit.

Well, there’s a problem. Three of the four thrusters on the spacecraft have been experiencing low performance, not generating as much oomph as they should. Engineers suspect clogged fuel lines. The thrusters have only been used for short duration bursts so far, but much longer ones are planned to give Flashlight the right velocity to achieve orbit, and the engineers hope this may unclog the lines.

I like these little space probes. They have a lot of bang for the buck, and can do amazing science and ground work (so to speak) for future, bigger missions. I hope that Flashlight can clear its lines soon and get on the right path.

Also, until I read the Flashlight press release I didn’t know NASA has a SmallSat blog! I’ll be keeping an eye on that, too.

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

There are a lot of weird things about Mars. A lot. Of all of them, though, one of the very weirdest is the Martian Hemispheric Dichotomy.

That’s a fun name, isn’t it? It refers to the fact that the two hemispheres of Mars are entirely different. In very broad terms, the southern hemisphere is mostly highlands; rough hills that are heavily cratered. The northern half, in contrast, is dominated by a huge smoother area that is on average much lower elevation (with the exception of the Tharsis volcanic bulge). This immense dip is called the Borealis Basin — the northern basin. It covers nearly half the planet, and is on average 10 kilometers lower elevation than the southern hemisphere.

Literally, walking from south to north on Mars is walking downhill.

Why?

The obvious idea is that something very, very large whacked into Mars near its north pole long ago. An asteroid upwards of 1,000 km across, perhaps, blasting so much material away from the impact site that it created the hemispheric dichotomy. This hasn’t ever been proven to the degree scientists would accept it as reality, but it seems the most likely explanation.

This is the fun part.

A paper recently published looked into the physics of the situation. There have been plenty of studies done in the past looking at how an enormous impact would shape Mars, but the planetary scientists who wrote the new paper thought it could be done better. They used a sophisticated simulation (called smooth-particle hydrodynamics, which uses the physics of how particles collide and interact in collisions) to look at what would happen. But they did something that hadn’t been done before: They included the physics of material strength.

That turns out to be critical. If the impactor hits ice, or rock, or water, or iron, the material will react differently. Many older sims also used equations that worked for smaller-scale events, but the scientists in the new work claim those don’t scale up to an impact this size well. In this work they tried to be as accurate as possible, so they used better equations.

What they found really surprised me: An impact in the northern hemisphere just doesn’t reproduce what we see on Mars today. They varied the size and speed and angle of impact, but no matter what they did the actual low northern elevations were never reproduced in the sims.

So they did what any good scientists would do: They let the simulated asteroid hit in the southern hemisphere. And lo: They got a good fit!

What they found is that after the impact the mantle under the crust bubbles up to form a huge magma ocean that covers the southern hemisphere, and when it solidified it actually raised the elevation by a lot. So it’s not that an impact scraped away the northern half, it’s that the impact released so much magma it built up the southern half.

And what kind of impact fit the data best? An asteroid 1,000 – 1,500 kilometers wide — bigger than any asteroid in existence today! — smacked into the austral Martian crust at a low 15°-30° angle at about 23,000 kilometers per hour. Holy yikes. The resulting cataclysm would’ve been obvious from across the solar system.

The biggest problem with their sim is that they predict an even thicker southern crust than exists now. They’re not sure why their simulations don’t get that right, but it could be due to special circumstances of the material composing the Martian mantle. They had to guess at that a bit and the actual situation there could be somewhat different, accounting for the difference.

If this pans out it’s a very interesting result, the opposite of what you might expect. It also means that we now have a better way to simulate very large impacts, which do happen. Well, they did happen long ago; they’re much more rare now. But we see evidence of impacts like that on a lot of solar system bodies, including the Earth and Moon. Understanding how they formed and the effects they had would really help scientists get a better grip on why these moons and planets are the way they are today. It also helps us understand what’s going on deep under their surfaces, which is hard to determine otherwise.

Our entire planet, and whole other worlds, were shaped by impacts. It’s about time we started knowing just what that means.

P.S. I talk about the hemispheric dichotomy, Borealis Basin, and more in my upcoming book Under Aliens Skies. The Mars chapter is like taking a tour of the planet as if you were there. If that’s you’re sort of thing — and I’m willing to bet it is since you read my newsletter — you’ll like this book, It comes out on April 18, 2023, and you can pre-order it here.

Et alia

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!