Friday was the 25th anniversary of the loss of the Shuttle Orbiter Challenger, which I already wrote about as part of a post about Apollo 1 and Columbia. But I wanted to add that after that event in 1986, seven craters on the Moon were named after the astronauts:

This mosaic of LRO images is about 190 km wide, so these craters are actually quite large. Interestingly, these craters are themselves inside a much larger 524-km wide impact basin… named Apollo.

Image credit: NASA/GSFC/Arizona State University

This is very cool: a guy got a grant to comb through satellite imagery to look for terrestrial craters, and found one hidden in plain sight! The Planetary Society has all the details. The man who found it studied geology in college, but is now a systems analyst!

This is a perfect example of citizen science. There’s too much real estate — on Earth and in the sky — for what we normally think of as geologists and astronomers to examine carefully. And this shows there’s plenty of room for "amateurs" to help out… and that word always makes me laugh. I know a lot of amateur astronomers who know far more than I do about pointing a telescope. You’ll almost always find that at their borders, most definitions are pretty fuzzy.

Tip o’ the Whipple shield to David Kessler.

Of all the moons in the solar system, Mimas is one of the most recognizable. And new pictures from Cassini show us again just why.

On Saturday, February 13, the Saturn probe dipped low over Mimas, sliding past the small moon at a distance of just 15,000 kilometers (9000 miles). For comparison, the Earth is about 13,000 km (8000 miles) across, so Cassini really threaded the needle with this pass.

On its way out from the encounter, when it was about 70,000 km (44,000 miles) from the moon, it snapped this astonishing shot:

Yegads. Note that this image is raw and unprocessed — it’s basically straight off the camera (and converted to JPG). But holy cow, there’s a lot to see. The giant crater Herschel is pretty obvious. It’s about 130 km (80 miles) across (compare that to Mimas itself, which is 400 km in diameter!), with a central peak characteristic of large impact basins. I think that’s where the main weapon is located.

Mimas has clearly had an interesting past: it’s battered beyond belief, loaded with impact craters. In fact, one thing scientists hope to learn from this pass of the moon is a bit of its timeline. By counting up the number of craters inside Herschel, and comparing that to the crater counts outside of it, they can estimate its age. Fewer craters inside of Herschel means it’s younger than the surrounding surface, for example. But how much younger? Maybe we’ll soon know. And they’ll be able to see craters that are pretty small; the resolution in the image here is about 200 meters (1/8 mile) per pixel. That’s about the same as we can do on our own Moon from Earth!

Sometimes with raw images like this, the background can be a little screwed up due to artifacts in the camera. But in this case, the glow on the left hand side of the big image is quite real: it’s the face of Saturn itself! The geometry of the shot was just right to capture a bit of the cloudtops of the ringed world. Very cool.

These are gorgeous pictures, and it’ll be nice to see them once they’re completely processed, too. We’ll learn a lot about the moon from them… and as far as Mimas goes, I just hope it’s not fully armed and operational. I suppose I shouldn’t be too worried though. After all, I used to bullseye womp rats in my T-16 telescope, and they’re not too much bigger than Mimas.

Image credit: NASA/JPL/Space Science Institute

Last week, the MESSENGER spacecraft passed the solar system’s smallest planet for the third and final time; when they next meet it won’t be some quick fling, it’ll be for a long term relationship.

Several gorgeous images were returned from the spacecraft, but this one is my favorite so far:

This is a large impact basin about 260 km (160 miles) across. It’s never been seen before! Only one other spacecraft has visited Mercury before — Mariner 10 in 1974 — and its orbit was such that it never did see many parts of the planet. MESSENGER was in the right place at the right time to snap this picture.

Note that it’s a double ringed crater. It’s not quite clear why these features form. It may be due to the forces generated upon impact, when a shock wave travels through the rock and rebounds inside the crater, or it may be from subsequent volcanic flows. Double rings are only seen in large impact events, so that must have something to do with it. You can also see concentric troughs or cracks in the crater middle. Those are due to the stretching of the crater floor after the impact.

Other images of Mercury from this third pass are just as cool: a bright splash around a double crater (seen here; most likely lighter material under the surface blasted out on impact), a crater with an elongated pit in its floor that makes it a pretty good smiley face, and a lovely shot of the northern limb of the planet spattered with craters.

I imagine they’ll release a handful more images over the next few days, but that’ll be it for the most part until March 2011, when MESSENGER meets up with Mercury one last time, settling into orbit… and then we’ll see lots more images. Lots and lots more… and they’ll be even higher resolution than these. What wonders will we see then?