Image: SOHO (ESA AND NASA), LASCO AND UVCS
Hurtling toward the sun at nearly a million kilometers an hour, Comet C/2001 C2 (SOHO) met with a fiery death in February¿but not before instruments on NASA's SOHO spacecraft captured the kamikaze streaker on film. Spotted earlier this month by comet hunters in Germany and China who accessed the images via the Internet, C/2001 C2 (SOHO) is one of nearly 300 comets SOHO has discovered since 1996. Like most of the others, this latest comet belonged to a family of "sungrazers" that scientists believe were once part of a large comet that fragmented long ago.
Both SOHO's visible light coronagraph, LASCO, and its ultraviolet coronagraph, UVCS, observed the comet. In the picture at the right, two of the UVCS images are shown superimposed on a LASCO image. The first UVCS image, taken when the comet's head was 2.7 million kilometers from the sun's surface, shows the comet's broad, well-defined gas tail, reaching more than half a million kilometers in length. In the second UVCS image, taken an hour later, the comet's head is 1.6 million kilometers from the sun, and the comet appears to be flying in a region of significantly higher solar wind density.
The ultraviolet light in these pictures comes from hydrogen atoms formed during the breakup of water vapor released from the comet by the heat of the sun. Estimates based on these pictures indicate that C-201 C2 (SOHO) was giving off steam at about 100 kilograms per second and that its nucleus was only 10 to 20 meters across. Larger objects, such as Halley's Comet, in contrast, feature nuclei measured in kilometers.