Credit: C Lisse, M. Mumma (GSFC)/K. Dennerl, J. Schmitt, J. Englhauser (MPE)

A Million Degree Snowball

Comets are often thought of as "dirty snowballs", since they're primarily composed of ice and dust. Who would have expected that these snowballs could be surrounded by million-degree gas? It seems a surprising thing, but in fact comets are surrounded by extremely hot gas, for at least part of their travels around the sun. The presence of this superhot gas was detected for the first time on March 27, 1996 by scientists at the Goddard Space Flight Center and the Max Planck Institut fuer Extraterrische Physik by studying images of the comet Hyakutake taken by the High Resolution Imager on the ROSAT X-ray observatory. This superhot gas generally lies between the comet and the sun, and perhaps is produced by the exchange of electrons from the cometary gas and the solar wind material as the comet moves around the sun. The gas is far enough away from the comet itself, and has very low density, so there's no danger that the comet itself will melt.

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Each week the HEASARC brings you new, exciting and beautiful images from X-ray and Gamma ray astronomy. Check back each week and be sure to check out the HEAPOW archive!

Page Author: Dr. Michael F. Corcoran
Last modified May 26, 2001