Category Archives: moons

enceladus, moons, skiing

Ski Enceladus

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Check out the Moguls!

Back in my grad school days my officemates and I decided to take up skiing as a respite from the heavy workload and stress of first-year studies. We formed what became known as the “Klingon Ski Team” and our charge was to “ski with honor!”  The University of Colorado was within an hour or two’s drive of several decent ski areas, and so we skiied with honor as best we could, hardly missing a weekend except during the December holidays, when the slopes were packed with tourists.

Cairo Sulcus on Enceladus, taken by Cassinis narrow-angle camera.
Cairo Sulcus on Enceladus, taken by Cassini's narrow-angle camera. Image size is 1024 x 1024; scale is 10 meters per pixel.

I was reminded of those heady days of Klingon sitzmarks and fearless mogul-jumping when I saw this image of the surface of Saturn’s icy moon Enceladus in the Boston Globe’s “Big Picture” section yesterday.

These ridges and folds are actually wrinkles in the icy crust and some of those chunks of ice are a couple of hundred meters across.  This place would provide some incredible ski runs, if you could figure out a way to get there and get the appropriate ski gear (including oxygen tanks and life-support suits) and find a chopper to drop you for some extreme outer solar system skiing.  Klingons would do it!

Mars Express, moons, phobos

Orbiting Piles of Rubble

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Where Do They Come From?

Phobos as seen by Mars Express
Phobos as seen by Mars Express

Not everything in the solar system is as solid as it looks at first glance. Take Phobos, the larger moon that orbits Mars. It looks solid, but it may well be an orbiting pile of rubble. Now where would that rubble come from?  Most likely a collision of some kind.

The European Space Agency’s Mars Express mission passed by Phobos this past summer and took a series of high-definition stereo images and data. That information got fed into a 3D modeling program that is letting astronomers measure this moon’s characteristics, including its volume and the interacting gravitational tugs between Mars and Phobos.

The analysis suggests that Phobos may be more of an asteroid than a body that evolved as a single piece.

The closest match that scientists can make for Phobos is with D-class asteroids, which are highly fractured and riddled with caverns. They are really more like pieces of rock that stick together by gravity. Scientists refer to these loosely grouped rock piles as “rubble piles.”

So, if it’s likely that Phobos didn’t form around Mars, how did this orbiting rocky junkyard get into its current equatorial orbit around Mars?  There are two ideas. First, Mars gravitationally “captured” a passing rubble pile, which settled into orbit as Phobos. Deimos, the other moon, was likely captured the same way.

Phobos: an orbiting rubble collection?
Phobos: an orbiting rubble collection?

The other possibility is that a meteorite (a chunk of rock from an asteroid) smashed into early Mars and pieces of it got blasted back into space. Eventually, they clumped together into a rubble pile of rocks bound together by gravity, forming what we know today as Phobos.

In the near future the Russian space agency will send a probe called Grunt to Phobos to do study this moon and collect samples of rock for further study.  Studies of rocks and continuing studies of Phobos’s subsurface structure (done using radars onboard the Mars Express spacecraft) will help astronomers figure out at least some of Phobos’s past and possibly even its origin.

As they say: stay tuned!

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