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The origin of pits on 9P/Tempel 1 and the geologic signature of outbursts in Stardust-NExT images

By Mike Belton, Co-Investigator

The origin of the circular pits that are distributed across the surface of comet Tempel 1 in an irregular band following high terrain in Stardust-NExT images is analyzed. A few are shown to be either collapse features analogous to terrestrial calderas and associated with eruptive cryo-volcanic flows or impact craters, which is the result of impacts with asteroidal material.

The vast majority are shown to have been caused by cometary outbursts, another form of cryo-volcanic activity. This follows from the observed rate of occurrence of outbursts observed in the Deep Impact mission and Earth-based observations as compared to the large number of pits seen on the surface.

To examine their geologic signature we found that the location of the mini-outbursts observed by Deep Impact fell within images taken by Stardust-NExT. The mini-outbursts apparently leave behind closely packed groups of pits of similar size. The size distribution of Tempel 1's pits is shown to be identical with those seen previously on comet Wild 2, even though the visual appearance of the pits on the two comets is quite different. We suggest that this difference in appearance is an evolutionary effect.

Finally, we use the observed size distribution to develop rough relationships between the magnitude of an outburst, its energy release, and the size of the resulting pit. We show that Tempel 1 probably experienced mega-outburst activity in its past.

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“When we see comets up in the sky they're really spectacular. But unless you get close to a comet, you can't really figure out what's going on.”

-Joe Veverka