Phobos is, like, totally groovy

Bad Astronomy
The entire universe in blog form
Jan. 24 2011 7:00 AM

Phobos is, like, totally groovy

As recently promised, the European Space Agency's Mars Express probe made a very close pass of the small moon Phobos, taking incredibly detailed pictures of the spud-shaped rock. Emily Lakdawalla, as always with planetary missions, has the what-fors with this event.

When it was a mere 111 km (66 miles) from the moon, Mars Express took this amazing image:

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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Click it for the full-res version is a whopping 7800 x 5200 pixel, 13 Mb TIF barsoomenated version. The detail is incredible, with features as small as 8 meters (roughly 25 feet across). Since Phobos is about 27 km (17 miles) long, that's a lot of detail!

But as regular readers know, I have a thing for 3D red/green anaglyphs, and as the probe passed the moon naturally took stereoscopic images. The folks at ESA put two together to make this jaw-dropping 3D shot of Phobos:


Click it to get 3800 x 2600 pixel, 13 Mb TIF version. You really want to. If you have red/green glasses, this is one of the best anaglyphs from space you'll see. I've never seen something stick out of my screen like this! Also, the details were so sharp that if I shake my head back and forth (like gesturing "no") I can actually see Phobos rotate a little bit, due to the change of positions of my eyes! That was new to me as well, and is very cool. it really solidifies the illusion that you're seeing an object three-dimensionally.

Mars is an astonishing place, and it's easy to forget how interesting its two moons are (the other is Deimos, which is smaller than Phobos). Their origins are still something of a mystery, and the surface features on Phobos are not totally understood either. Specifically, all those parallel grooves are pretty weird! The current thinking is that they were actually caused by impacts on Mars! It works like this: some giant rock hits Mars and blasts vast quantities of material up and out, some of which reaches up into space (Mars has a thin atmosphere and lower gravity than Earth). Phobos plows into this material, and the direct impacts with big chunks can form craters. But material from impacts on Mars is likely to be ejected in plumes (see, for example, rays around the crater Tycho caused by impact plumes on our own Moon). Hitting those would leave long, linear gouges in the surface. Grooves!

As incredible as it sounds, the evidence does point to this scenario; for example, a lack of grooves on the trailing part of Phobos, where ejecta from below couldn't reach because of Phobos' forward orbital speed (like how rain hits preferentially on a car's front windshield and not the back).

Of course, hypotheses like this live and die on the evidence, so more data and more detailed images of Phobos are always welcome. Mars Express still orbits the Red planet and hopefully will continue to collect such evidence for a long time to come.

Image credit: ESA/DLR/FU Berlin (G. Neukum).



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