Night of the Comet

In Comets by Brian Koberlein2 Comments

The Rosetta spacecraft has successfully moved into orbit around 67P/Churyumov-Gerasimenko. We’ve been getting images of the comet as Rosetta approached, but now that it’s in orbit we are getting high resolution images such as the one above. You’ll notice the comet really looks like an asteroid, with what seems to be a rocky/dusty surface. That’s because comets and asteroids aren’t as different as often portrayed.

Comets are so-named because they exhibit tails of gas and dust when passing through the inner solar system. These tails are due to volatiles such as methane and water ice on the surface of the comet. We have also seen asteroids exhibit similar tails of dust, though it isn’t as common.

The nucleus of Comet Halley. Credit: NASA

The nucleus of Comet Halley. Credit: NASA

This is the first time we’ve been able to place a satellite in orbit around a comet. We’ve had several flyby missions for comets, including the famous flyby of Comet Halley by the Giotto spacecraft. One huge advantage of having an orbiter is that we can make a long-term study of the comet. Rosetta has arrived at 67P/C-G just before it begins its journey through the inner solar system, so the mission will provide a first hand look at how comets are warmed by the Sun and begin to form a tail.

One of Rosetta’s first missions, however, will be to find a good landing spot for its companion spacecraft Philae. That landing should occur sometime in mid-November.


  1. This is just such an amazing feat I am nearly speechless to express my awe at this achievement. I can hardly wait for the resultsbofbthe further study. Thanks for covering this – I had not been aware of it before today.

  2. This is an outstanding opportunity to observe and measure in situ the physical and electromagnetic properties of a comet. Contrary to what Phil Plait has stated in his article on the Slate website, there is no evidence here – yet – that it is an “icy” body. Others have termed comets “dirty snowballs”. So far none of our visitors have indicated anything other than rough, rocky, possibly semi-metallic bodies in a variety of shapes and degrees of chaotic terrain. They look for all the world, other than scale, like lumps of slag from a blast furnace. Observations of hydroxyl ions in plumes may indicate water as one possible source, but other chemical breakdowns of minerals can also produce hydroxyl that shows up in the same place in the spectrum as water-sourced hydroxyl.

    If Philae, the lander, can drill down and obtain samples below the surface, and analyze them, it should shed a lot of light as to whether a comet is simply an asteroid on an elongated orbit with interesting interactions between itself and the changing solar plasma or “wind” as it moves through the interplanetary portion of the heliosphere. If the radar tomography experiment works, it should shed even more light – so to speak – on this body’s internal geological structure. Lots more to come!

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