A long time ago, something really, really, really BIG hit the Moon. Hard. The explosion was huge beyond human grasp, and when it was all done, the hole it left on the Moon was 900 km (600 miles) across!

Behold, Mare Orientale:

This image was taken by the Lunar Reconnaissance Orbiter’s Wide Angle Camera, and shows the entire basin. It’s located just over the edge of the Moon as seen from Earth, so we can only get hints of it when we look from home. LRO can see it in all its neck-hair-raising glory.

See all those radial features emanating outward from it? Those are crater chains: secondary impact events as huge chunks of debris hundreds of meters or even kilometers across were thrown hundreds of kilometers away by the force of the impact!

Yegads. You can see these better in an interactive pan-and-scan image that allows you to zoom in to scales of 100 meters per pixel. It’s incredible.

But looking at the central part itself, I got a funny familiar feeling. I read reddit, after all. Was the Moon… trolling us?
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The Lunar Reconnaissance Orbiter has been taking extreme close-ups of the Moon since September 2009, and since that time I’ve posted dozens of these images, including shots of the Apollo landing sites, images of Earth from the Moon, craters, lava tubes, and more. But among my favorite of all these are the ones showing action, something that’s happened that you can actually see. And the best of these, I think, are from boulders rolling around on the Moon’s surface. Like this one!

[Click to embiggen and get a somewhat wider view.]

That boulder you see there is about 30 meters across — 100 feet — so it’s pretty big, the size of a house. It’s sitting inside the 110-km-wide crater Gassendi, and rolled down from the crater’s central peak. The trail is obvious, as are several smaller ones around it.

Funny– it seems obvious in retrospect (as so many things do), but I wouldn’t have predicted boulders rolling down slopes on the Moon. In my mind, even now, it’s hard to shake the prejudice that the Moon is dead, dead, dead. But it still has some activity; for example, the changing gravity it feels from the Earth as it loops around us in its elliptical orbit causes the Moon to stretch and compress. This can create seismic activity — moonquakes! And that can cause rocks to tumble downslope.

See? Obvious.

There are lots of images from LRO of this, too. Here’s one with rolling rocks and trails in Tsiolkovsky crater, and one of my all-time favorites shows a boulder that rolled down a slope and into a small crater: a lunar hole in one!

Back to that big guy up top; Gassendi was a landing target for Apollo 17 for a while, but the uncertain terrain (lunain?) made the planners decide to go elsewhere. Too bad: boulders that roll down from higher locations make it easier to get rock samples from different areas, since the rock already did the work of coming to you!

But maybe, just maybe, we’re not quite done with the Moon yet. I hope to once again see people walking on its surface, and instead of seeing pictures like this from above, we’ll have shots of astronauts living and working there, taken by their own hands.

Image credit: ASA/GSFC/Arizona State University

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

When I made my Top 14 Astronomy Pictures of 2010, it was really tough cutting some out. This is a gallery of the images that, for whatever reasons, I decided to leave off. They’re still spectacular and gorgeous, though! Click on the thumbnail in the slider to go to an image, use the arrows to navigate back and forth, and click on the big image displayed below to get more info and a bigger version if available.

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Use the thumbnails and arrows to browse the images, and click on the images themselves to go through to blog posts with more details and descriptions.

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I live less than an hour from some spectacular Rocky Mountain peaks. The view from up there is always magnificent, and when we hike we’re always curious about just how high we are. 11,500 feet? 12,000? That knowledge isn’t necessarily useful, but it’s fun.

Hiking in the Moon is a different matter. How would you know how high up you are? Well, if you had the elevation data made by the the Lunar Reconnaissance Orbiter you’d be all set, because then you’d know that if you were at a latitude of 5.4125° and longitude of 201.3665°, you’d be on the highest spot on the Moon!

[Click to enelevate.]

See that red arrow? That's the spot. If you stood there, you'd be 10,786 meters (35,387 feet, about 6.7 miles) above the average lunar elevation^*.

Funny, too: as soon as I saw that, my first thought — after wondering just how high up it was — was how steep the slope is there. Turns out the LRO folks wondered too, and found that a hike up to that point wouldn’t be very taxing, since the slope is about 3°. That’s a 5 meter rise for every 100 meters hiked. I do some hiking here in the Rocky Mountains, and that slope wouldn’t be too tough. On the Moon, with 1/6th gravity, it would be a snap.

Of course, the air is a bit thinner there.

According to the LRO page, this region of the Moon has such a high elevation probably due to the monster impact that formed the 2500-km-wide Aitken Basin at the Moon’s south pole. The debris piled up all over the place, and near this position would’ve been tremendous. Imagine! Several billion years ago, an asteroid perhaps 200 km (120 miles) across [200 kilometers across aiiieee!!!] plows into the Moon at a speed 30 times faster than a rifle bullet. A huge hole is excavated, and all that debris has to go somewhere. Even on the lunar equator, 2700 km (1600 miles) away, ejecta material falling piles up to depths of 10,000 meters! Incredible!

Still and all, I was trying to think of some sort of scientific use of knowing where this particular point on the Moon is. I’ll be honest: I’m not sure there is one. I mean, sure, having elevation maps is interesting and useful, and knowing where places have higher elevation can lead to insight into formation mechanisms and all that.

But knowing where the actual highest point is?

Well, maybe there isn’t scientific usefulness for it. But you know what? It’s cool. And sometimes that’s enough.

Image credit: NASA/GSFC/Arizona State University

Clearly defeated in their attempt to destroy the galaxy with a laser, NASA sets its sights somewhat closer and tries to destroy the Moon:

Cooooool. Actually, while that is a laser, it’s a bit too low power to do any damage to our friendly Moon. But it does have enough to help NASA track satellites! It’s part of the Goddard Space Flight Center’s Laser Ranging Facility in Maryland. We know the speed of light very accurately, so if you ping a satellite with a laser beam you can time the pulses and very accurately determine the satellite’s position.

In this case, two beams were being used to track the position of NASA’s Lunar Reconnaissance Orbiter, one of my favorite space missions of all time (to see why, check out this gallery of images I posted recently).

I used to work at Goddard, and I remember going to this facility once because it was a dark site from which I could try to spot a comet that happened to be passing us at the time. The laser was being used, and it was positively awe-inspiring and quite surreal to see it streaking up into the sky. And yes, they have to keep a careful eye out for airplanes and such flying past. While that beam isn’t enough to melt a satellite, it’s certainly enough to fry a pilot’s eyes!

Which is why you don’t want sharks equipped with these things. Really, that’s just asking for trouble.

Image credit: NASA