Zoom in on a HUGE lunar bullseye

Zoom in on a HUGE lunar bullseye

Zoom in on a HUGE lunar bullseye

Bad Astronomy
The entire universe in blog form
June 19 2010 8:49 AM

Zoom in on a HUGE lunar bullseye

If you've ever wanted to download a ginormous image of the Moon and explore it, now's your chance: the Lunar Reconnaissance Orbiter Camera folks have released a monster 185 megapixel image of one of the biggest smackdowns on the Moon: Orientale Basin.

lro_orientale

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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Yowza! Click to get the 1400 x 1400 pixel PNG, or you can try to swallow the 122 Mb TIF at the full resolution of 13,590 x 13,590 pixels!

Orientale is a vast impact basin, the hole left by an asteroid that hit the Moon about three billion years ago. Looking like a humongous bulls-eye, it's a multi-ring crater, and the outer ramparts are a full 950 km (590 miles) across. That's half again bigger than my home state of Colorado.

To give you an idea of just how big this is -- and also, to be honest, to scare myself a little -- I superimposed the picture of Orientale on a map of the United States. This is to scale, folks:

us_orientale

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Holy. Frakking. Crap. Whatever hit the Moon to create this basin must have been about 100 kilometers (60 miles) across. That would have made it 1000 times the mass of the asteroid that wiped out the dinosaurs. If something like that hit the Earth today, there would be no life left on our planet. At all. Happily, nothing that big is headed our way.

Oh, but what a sight that must have been. An impact that size would release the energy of 100 billion one-megaton hydrogen bombs. It would have been visible across the solar system! Amazingly, though, such events were a little more common back then; the solar system used to be filled with monster asteroids itching for a fight. That period of bombardment ended billions of years ago, though. Yay.

The image from LROC is pretty amazing. It's actually a mosaic of quite a few individual images from the Wide Angle Camera. The resolution is about 100 meters per pixel in the full image. If you don't want to download that big picture, you can interactively zoom in on the basin on the LROC website. The black areas are where data are missing (or where the Moon is modest, perhaps).

You can see that Orientale is not like other craters. The event was so huge that it punched right into the Moon, like a fist through a styrofoam sheet, and the crater left behind got partially filled up with lava. That's why there's no obvious rim and bowl shape you usually see in smaller craters. The multiple rings are not fully understood -- it's rather hard to model an impact that releases the energy of a few billion nuclear bombs -- though they are common in giant impacts. It may be that waves of energy blasting out from the impact event ripple through the ground like earthquakes, and where they rebound and interact you get those rings.

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Since the original event, other, smaller impacts have dotted it, but again I refer you to the map of the US above to see what "smaller" means in this case! Some are bigger than cities and counties. Surrounding the inner part of the basin is terrain loaded with scarps (steep cliffs), gullies cut by flowing lava, and cracks caused by the shifting landscape. It's really worth your time to simply scroll around the interactive map and see what's there. And remember, at highest zoom each pixel is about the size of a football stadium.

Friday, June 18, 2010 was the first anniversary of the launch of LRO. Consider this image a fantastic present to us!

Image credit: NASA/GSFC/Arizona State University