Comet Ikeya-Seki, photographed by Roger Lynds at Kitt Peak, Arizona, on the morning of October 29, 1965.
Credit: NASA / Roger Lynds
"The storm began on Dec 13th and ended on the 22nd," said Karl Battams of the Naval Research Lab in Washington, DC. "During that time, the Solar and Heliospheric Observatory (SOHO) detected 25 comets diving into the Sun. It was crazy!"
Sundiving comets — a.k.a. 'sungrazers' — are nothing new. SOHO typically sees one every few days, plunging inward and disintegrating as solar heat sublimes its volatile ices. "But 25 comets in just 10 days, that's unprecedented," said Battams.
"The comets were 10-metre class objects, about the size of a room or a house," noted Matthew Knight of the Lowell Observatory in Flagstaff, Arizona. "As comets go, these are considered small."
SOHO excels at this kind of work. The spacecraft's coronagraph uses an opaque disk to block the glare of the sun like an artificial eclipse, revealing faint objects that no Earth-bound telescope could possibly see.
Every day, amateur astronomers from around the world scrutinise the images in search of new comets. Since SOHO was launched in 1996, more than 2000 comets have been found in this way, an all-time record for any astronomer or space mission.
Battams and Knight think the comet-storm of December 2010 might herald a much bigger sungrazer to come, something people could see with the naked eye, perhaps even during the day.
"It's just a matter of time," said Battams. "We know there are some big ones out there."
Comet Ikeya-Seki is a good example. In 1965 it appeared out of nowhere, dove toward the Sun and swooped over the stellar surface only 450,000 km away. Because Ikeya-Seki's nucleus was large, about 5 km wide, it survived the encounter and emerged as one of the brightest comets of the past thousand years.
Japanese observers saw it in broad daylight right beside the morning Sun. People watched in amazement as Ikeya-Seki fell into at least three pieces before receding back into the solar system. Similar but lesser sungrazing comets were observed in 1843, 1882, 1963 and 1970.
These sungrazers are all related to one another. Astronomers call them the 'Kreutz family' after the 19th century astronomer Heinrich Kreutz who first studied them as a group. Modern thinking about the family is attributed to Brian Marsden (1937-2010) of the Harvard Minor Planet Centre.
