Saturday, November 15, 2014
Comets Are Weird
Philae was one of two robot spacecraft launched over ten years ago. Rosetta was the larger of the two, and still orbits Comet 67P.
Philae bounced twice, and landed in a place that was mostly in shadow and so starved for solar power It continued to transmit data until only enough power was left from her batteries to put the craft in hibernation, and it uploaded quite a lot. Plucky robot.
It gave us images of the surface. The one above is the strangest landscape beyond Earth's surface I have seen to date.
But wait, there's more.
We have known for some time that the nucleus of the typical comet is mostly fluffy; typically about half the density of water. They have been described dirty snowballs or snowy dirt balls.
But wait! Some of the uploaded data already show a more complicated picture than we thought. One of Philae's experiments, MUPUS, was designed to hammer one of its sensors into the surface of the comet. The surface turned out to be much harder than expected, and apparently broke the probe.
Perhaps we should think of comets not simply as dirty snowballs, but dirty snowballs that a cosmic prankster dipped in water and then left at subzero temperature until the exterior was as hard as rock. Alternatively, this might be a condition peculiar to impact craters on comets, and Philae happened to fall into one. But Philae also bounced pretty hard at the first landing site.
Or one might think of the comet as a a deep space Mallomar, or in this case a chocolate dipped Peep: a hard crust around a fluffy interior. But the reality is probably still more complex than that, with all but the most recent crater floors dusted with ejecta from later impacts.
And even the fluffy parts of the comet might include large chunks of less fluffy matter: dirt, rocks or ice.
Update: As of November 18, ESA scientists say the data received so far suggests 4-8 inches of dust over hard ice, and a fluffy porous interior below that.