Kreutz Sungrazers - Recent Observations

Recent Observations

Until recently, it would have been possible for even a very bright member of the Kreutz Sungrazers to pass through the inner solar system unnoticed, if its perihelion had occurred between about May and August. At this time of year, as seen from Earth, the comet would approach and recede almost directly behind the sun, and could only become visible extremely close to the sun if it became very bright. Only a remarkable coincidence between the perihelion passage of the Eclipse Comet of 1882 and a total solar eclipse allowed its discovery.

However, during the 1980s, two Sun-observing satellites serendipitously discovered several new members of the Kreutz family, and since the launch of the SOHO Sun-observing satellite in 1995, it has been possible to observe comets very close to the sun at any time of year. The satellite provides a constant view of the immediate solar vicinity, and SOHO has now discovered hundreds of new sungrazing comets, some just a few metres across. About 83% of the sungrazers found by SOHO are members of the Kreutz group, with the other being referred to as 'non-Kreutz' or 'sporadic' sungrazers (Meyer, Marsden, and Kracht1&2 families). Apart from Comet Lovejoy, none of the sungrazers seen by SOHO has survived its perihelion passage; some may have plunged into the Sun itself, but most are likely to have simply evaporated away completely.

More than 75% of the SOHO sungrazers have been discovered by amateur astronomers analysing SOHO's observations via the Internet. Some amateurs have managed remarkable numbers of discoveries, with Rainer Kracht of Germany having chalked up 176 identifications, and Michael Oates of the United Kingdom making 144 discoveries. As of October 2008, 1500 Kreutz Sungrazers have been identified.

SOHO observations have shown that Sungrazers frequently arrive in pairs separated by a few hours. These pairs are too frequent to occur by chance, and cannot be due to break-ups on the previous orbit, because the fragments would have separated by a much greater distance. Instead, it is thought that the pairs result from fragmentations far away from the perihelion. Many comets have been observed to fragment far from perihelion, and it seems that in the case of the Kreutz Sungrazers, an initial fragmentation near perihelion can be followed by an ongoing 'cascade' of break-ups throughout the rest of the orbit.

The number of Subgroup I Kreutz comets discovered is about four times the number of Subgroup II members. This suggests that the 'grandparent' comet split into parent comets of unequal size.