While staring virtually nonstop at the sun for nearly a decade, the Solar and Heliospheric Observatory (SOHO) satellite has discovered hundreds of comets—roughly half of all that are known. In August, an amateur astronomer analyzing SOHO images found the 999th and 1,000th of these icy chunks detected by the spacecraft.
Toni Scarmato, a high school teacher and a graduate student at Bologna University in Italy, identified the two comets as part of the Kreutz group of sun-grazing comets. About 85 percent of the comets found by SOHO belong to this group, whose members have similar orbits and pass within 800,000 kilometers of the sun’s surface, less than one-seventieth Mercury’s distance from the sun.
At this distance, the sun’s heat and gravity easily break comets apart, and each member of the Kreutz family may be a fragment of what had once been a single large comet. Indeed, many comets in this family are so small—about the size of a house—that they can’t be seen with ground-based telescopes. An instrument aboard SOHO can detect these comets because it has a large field of view and masks the sun’s blinding light.