The MESSENGER spacecraft, orbiting Mercury for nearly a year now, took this pretty nifty shot of the tiniest planet’s south polar region, showing deep, dark craters in the Goethe basin:

This region is about 300 km (180 miles) from the true south pole of the planet. On Earth that might be a cold spot, but on Mercury, cold spots are hard to come by.

… however, see how dark those craters are? Since they’re near the pole, the Sun never gets far above the horizon for them, and the crater floors are shrouded in perpetual darkness. That does make them cold! Well below the freezing point of water, it’s thought. Interestingly, radar observations of Mercury have indicated something in the crater floors is highly reflective, and water ice fits that bill. It’s not at all confirmed, but it’s entirely possible Mercury — a planet hot enough in the open Sun where zinc can exist as liquid lakes on the surface — might have frozen lakes of ice locked in crater bottoms near its poles!

While gazing idly at this picture, another thought popped into my head. (more…)

Last night, at 02:56 UTC, it was the 42nd anniversary of humans putting a bootprint on another world. Before Apollo 11 touched down on the Moon, though, NASA and the USSR sent a fleet of unmanned probes there. Since that time we’ve sent many more, including the Lunar Reconnaissance Orbiter, one of my favorite spacecraft of all time. It takes amazing high-res images of the Moon… and to celebrate today’s anniversary, they released this mysterious picture:

Cooool. Click to enlunenate.

This image is about 400 meters across, and shows an impact site with two lobes of material laid down to the sides. This butterfly-shape is a clear indication of a low-angle impact; it’s seen on many bodies in the solar system including the Moon, Mars, and even Earth (though the physics of exactly how the bi-lobed patterns form is still not well understood). Features like this are very rare… but it’s known that when a satellite orbit decays, it will impact at a low angle.

As the LRO site notes, in October 1967, the Lunar Orbiter 2 spacecraft impacted the lunar surface, possibly very near this spot. Could this be the final resting ground of an early NASA robotic explorer? It’s hard to say. When something hits hard enough to excavate material, it’s common to see ejected junk of different brightnesses, and here we see the dark patterns overlaid on a brighter surface. If that’s the impact area, though, the size of the impact looks too big for the mass and speed of the probe. Maybe it coincidentally hit a brighter area, but that stretches credulity, given the darker area all around.

So what happened here? The folks at LRO are planning follow-up observations to see if they can get pictures at a different Sun illumination angle, which will make any crater easier to spot. That might clear things up.

Or it might not. The Moon is the nearest astronomical object in the heavens by far, but it also has 38 million square kilometers of surface to explore! That’s four times the size of the Unites States… and LRO sees it at a resolution of roughly a half a meter. That’s a whole lot of pixels, and a whole lot of landscape in which to hide fun little mysteries. I hope there are many, many more.

The Dawn spacecraft is now in orbit around the main belt asteroid Vesta! Yay!

The spacecraft entered orbit around the main belt asteroid on Saturday, July 15. Two days later — today — it snapped this spectacular high-res image:

[Click to enprotoplanetate.]

Wow, what a mess! As expected, it’s littered with craters, but there are some interesting things to note. Some craters appear to be very deep, while others are shallow — that indicates a different type of terrain (asteroidain?) where the impactors hit (although in some cases it might be a lighting effect; a more direct sunlight angle makes craters look shallow). The grooves I mentioned in a previous post are everywhere, some looking more like scarps (cliffs) now. And look at that huge cliff on the upper right! I’ll be very curious to see that area at different angles. Is it part of a big basin, a collapse feature? Or is it a cliff caused by cracking in the surface? By the way, that lump in the center casting a shadow to the left is actually a mountain or mound of some kind well over 100 kilometers across.

The resolution is stunning; each pixel in the high-res version is about 1.4 km (0.9 miles) across — the asteroid itself is 530 km (330 miles) wide. Dawn is orbiting at a distance of 16,000 km (9900 miles; a bit more than the diameter of the Earth) and will slowly lower its orbit over time. Vesta’s mass is uncertain, so engineers played it safe and put it into a high orbit. This will allow an accurate mass to be determined, and then scientists and engineers can calculate how much thrust is needed to safely close in. That will take some time, about three weeks. During that time Dawn scientists will search the region around Vesta for tiny moons. None has ever been seen from Earth, but there’s nothing like being there.

… and I’ll add, we almost didn’t go. Back in 2005/6, this mission was actually canceled by NASA, causing quite the stir in the astronomy community. However, a strong voice was raised against this cutback, and Dawn was back on. After a long, long journey, it’s now where it belongs: in deep space, exploring, doing science, and expanding our frontiers.

I can hope the same will be true for JWST.

This is a pretty neat picture taken by the Lunar Reconnaissance Orbiter: two craters, side by side:

[Click to impactenate.]

What’s cool about it is the obvious age discrepancy between the two craters. The Moon lacks water and air, but it has erosion nonetheless: micrometeorite impacts, solar wind, and even thermal stress cause by the month-long day night cycle slowly wears away at the surface. Old craters have a rounded look to them, while fresher craters are sharp-edged, and show the debris from impact.

The full-res image has a scale of just a meter per pixel, so a lot of the smaller boulders you see around the younger crater on the right are the size of cars. Both craters are roughly 300 or so meters across; you could walk briskly across them in a couple of minutes.

I noticed the young crater has an odd shape, non-circular, almost diamond-shaped. Then I looked at other, nearby craters, and saw the same thing, so it must mostly be due to lighting. However, there is a funny hillock just to the right of the crater, and the boulder field around it is not symmetric; there are more above and below it. I wonder if there is a density change in the underlying rock just to the right of the crater, which helped shape the crater…?

That area is mostly flat lava flood plains, and in the zoomable and pannable larger-area context image there are some interesting features that look like very old crater rims poking up through the plain. Check it out! One of my favorite things about LRO is the pile of high-res pictures like this one you can zoom in an out of. It really helps give you a feel for what you’re seeing.

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What the heck hit Mars and made this?

[Click to barsoomenate.]

This image is from my favorite Red Planet paparazzo, the HiRISE camera on Mars Reconnaissance Orbiter. It shows three craters, each about 1.5 to 2 km (0.9 to 1.2 miles) across… and they all formed at the same time!

How can I tell? Well, for one thing, if this were a coincidence, with three impacts happening at very different times, then you’d see overlap in the crater rims; the earliest crater would be partially obscured by the later crater, and that in turn by the most recent impact. But that’s not the case here, since the rims aren’t overlaying each other. In fact, the straight walls between them are exactly what you’d expect if you have impact explosions happening simultaneously: the expanding shock waves smack into each other and create a linear feature.

Not only that, but let your eye follow the straight lines between craters up and down, above and below the craters themselves and onto the landscape. You can see that the hellish expanding wall of fire etched itself onto the Martian surface well beyond just the crater rims, and those linear features match the crater wall orientation. I annotated the image here to show you what I mean; the red lines are just outside the linear features.

I can picture what must have happened, millions of years ago over Mars…
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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.