They belong to the Kreutz family of sun-grazing comets, often seen by SOHO while diving towards their final rendezvous with the Sun. But as in humans, twins are rare! Even more so, this pair showed another very unusual trait: What looks like a faint tail (or "puff of smoke") can be seen moving away from the Sun, seemingly emanating from a point in the orbit beyond the comet's closest approach! Normally, sungrazers simply fade and disappear at an earlier stage, obliterated by the intense heat and pressure.

Another pair of Kreutz sungrazers with such a "headless tail" was observed in June 1998 (see MPEG [[an error occurred while processing this directive]] movie), when the observing geometry was very similar. But out of more than 600 sungrazing comets observed during more than six years by SOHO, this is only the third showing any signs of such behaviour!

The puff is most likely the dusty remains of the comet's nucleus, being pushed out by the radiation pressure after all the ice in the nucleus has evaporated, thus eliminating the processes maintaining a bright coma surrounding the core. Studies of the dust cloud may reveal clues to the size distribution of the dust grains.

Comets are balls of dust and ice that zoom around space in elongated orbits. Their dust tails are pushed by the radiation pressure from the Sun. Their ion tails (usually fainter) are pushed away from the Sun by the solar wind. Both tails point away from the Sun, even for comets that are travelling back outwards in the solar system.

Previous Picks of the Week

SOHO began its Weekly Pick some time after sending a weekly image or video clip to the American Museum of Natural History (Rose Center) in New York City. There, the SOHO Weekly Pick is displayed with some annotations on a large plasma display.

If your institution would also like to receive the same Weekly Pick from us for display (usually in Photoshop or QuickTime format), please send your inquiry to steele.hill@gsfc.nasa.gov.