The Sciences

Gettin' high on the Moon

Bad AstronomyBy Phil PlaitNov 3, 2010 4:03 PM


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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!

<br clear="all". [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

^* There's no water flowing on the Moon, so sea level isn't a useful standard. Instead, the lunar geoid is used; a sort-of average shape of the Moon using its gravity as a reference (go here and scroll down to #4). Getting this shape is really hard, and I imagine the laser altimeter on LRO will be used to refine the surface maps.

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