SOHO catches 3 new comets

From 29 till 31 March, a number of small chunks of ice and rock approached the Sun and became visible as tiny comets in the LASCO/C2 coronagraph on board the SOHO spacecraft. A coronagraph is an instrument that blocks out the solar disk so that the immediate vicinity around the Sun becomes visible, similar to what our Moon does during a total solar eclipse. Though SOHO's coronagraph is used to observe coronal mass ejections (CME), it has also made SOHO the most successful comet hunter so far. Indeed, late February, it had already 4138 comets on its very long list of comet discoveries since its launch in 1995. Quite a few of those detections were actually made by amateur astronomers ("citizen scientists") who were examining SOHO's imagery. SOHO's coronagraphs were never intended to chase comets, but their high sensitivity, wide field of view, and around-the-clock observing capability make them perfectly suited to see comets, in particular the ones that come very close to the Sun.

The 3 comets are visible in the clip and the annotated LASCO/C2 images underneath (the comets moving from the lower-left to the upper-right). The bright dot at the lower-left is the planet Venus. Only the second comet developed a visible (small) tail, the other two remained mainly dot-like in the C2 imagery. None of the three comets survived their close encounter with the Sun. In fact, as can be seen in the clip, they evaporated before they even came close to the Sun. The comets are members of the Kreutz family. This is a group of comets that all follow pretty much the same orbit that brings them very close to the Sun ("sungrazers"). It is believed that they are all fragments of a comet that broke apart several centuries ago. Most of the Kreutz members do not survive their intimate rendez-vous with the Sun. There are several other comet families, and a list with their apparent orbits as seen by the SOHO coronagraphs can be found at The Sungrazer Project website (C2/C3 comet tracks).  





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