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Earlier this month I wrote about a SpaceX Falcon 9 upper stage booster that impacted the moon on August 5. The rocket sent two missions to land on the lunar surface, and the upper stage, fuel spent, was in an elliptical orbit around Earth with an apogee (farthest point away from us) near the moon’s orbit. Over time, an impact was inevitable.

A lot of telescopes looked for the impact plume — the debris thrown up off the surface — but the only one with direct evidence I saw was from the IAA-CSIC (Institute of Astrophysics of Andalusia - Consejo Superior de Investigaciones Científicas) that shows the very faint material ejected.

However, now the crater from the impact has been seen directly in images from NASA’s Lunar Reconnaissance Orbiter, a mission that has been mapping the moon for over 17 years now. On August 11 and 12 it passed over the region several times, and took these very clear before-and-after shots:

The image covers an area about 400 meters on a side. The new crater is about 20 meters across, pretty much what was predicted. There is dark and bright material fanned out around the crater that was blown out by the impact. The darker stuff is from close to the surface, where exposure to sunlight radiation had already darkened the lunar surface, and the lighter stuff was excavated from deeper down.

There is some science to be had from this impact, like how the crater was formed, what the ejected material looks like, and more. But it also points a pretty big arrow at a pretty big problem. As humans send more probes and eventually people to the moon, this sort of unpredictable impact is a real danger. It’s not just the direct impact, either. Material thrown out from such events can travel many kilometers, which can be dangerous to sensitive machinery on the surface. Lunar dust is a horror of sharply angled particles similar to volcanic ash, and can foul moving parts, coat optics, and be a danger if breathed in (once it gets on spacesuits and machinery it can get into habitats).

There has been some work on this (here’s a good Space News article covering some of it) but we need international treaties about disposing of spent rocketry. If they are on orbits like the Falcon 9 was, it’s difficult or even impossible to predict exactly what they will do (there are multiple forces acting on such space litter — the gravity of the moon, Earth, and the sun, plus radiation pressure from sunlight). The bottom line is we can’t put rockets on these kinds of “disposal orbits” any more. 

It’s not clear to me how to avoid this; once a rocket is out of fuel there’s not much it can do. But then, we can make it illegal to launch a rocket that runs out of enough fuel to avoid such an orbit. That means more expense, delays, and difficulties, but that’s a small price to pay for safety of lunar astronauts.

It’s easy — and appropriate — to point to SpaceX for the blame here, but to be fair NASA and China have done this as well (according to Alice Gorman, aka Dr. Space Junk, this is the tenth rocket body to crash into the moon). There is a laissez faire attitude by many private space companies, though, when it comes to pollution and other environmental impacts. With the current regime in the White House I have no doubt nothing will get done about this, but it’s a critically important issue for the future. I hope enough countries take it seriously and get momentum going for an international treaty about it.

When the New Horizons spacecraft passed by Pluto in 2015 and started sending images to Earth, I remember watching the press conference where they showed close-ups of a region of smooth surface and I literally yelled out, “There are no craters!”

That’s critical because there’s no way to avoid impacts over time on an airless body. If the surface is smooth, that means it must have been resurfaced somehow, paving over older craters. On Earth that’s from tectonic processes, and on other bodies it might be lava (Io) or water ice (Europa) repaving the surface.

All these processes need energy in the form of heat to work, though. Pluto is tiny and frozen solid.

… isn’t it?

A new paper focuses on the Sputnik Planitia region, the iconic heart seen in the southeast part of Pluto. The western half is very smooth, and thought to be frozen nitrogen. Even at the time of the flyby, scientists speculated it could have liquid nitrogen beneath the surface welling up and freezing, creating the smooth feature.

The new work puts a lot of science behind the idea [link to journal paper]. The northern part of the “lobe” is broken up into segments reminiscent of polygonal ice segments in floating ice sheets on Earth. That was the first clue seen. But they point out the regions between the segments, the borders where they abut.

These areas are darker. Why? The authors look at several different mechanisms, but favor the idea that liquid nitrogen below the surface is seeping upwards (they posit basal melting of the glacier ice, the bottom melting due to pressure or warmer liquid below). As it pushes into the cracks it infiltrates the ice, making it darker (similar to how a snowball gets darker if it gets slushy).

This is a very interesting idea, even compelling, and supported by the physics they present, but isn’t conclusive. If I had to bet I’d say they’re right, but it’s hard to come to firm conclusions when we only have literal snapshots of Pluto — the entire flyby only lasted a few hours! I would love to see a lot more of these large trans-Neptunian objects seen up close, especially with orbiters that can stay and observe for a long time to look for changes. At the moment that’s not even in the planning stages, but dang, it sure would be cool to learn more about these weird and weirdly, surprisingly dynamic bodies out past Neptune.

I will be attending the March on Washington DC on Friday, August 28, 2026. This is on the anniversary of Martin Luther King Jr.’s march in 1963, and is in his honor to publically defend the right to vote. You can read all about the march on their website, which includes logistics. It’s hosted by Al Sharpton, and speakers include Bernie Sanders and AOC; I think she’s a great orator so this will be exciting. The whole thing starts at 09:00, so if you attend be sure to plan accordingly. We’re staying with friends in DC the night before and taking the Metro in, for example. I hope y’all will attend!

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!