C/2011 W3 (Lovejoy)

Lore & Background

Comet Lovejoy was discovered on 27 November 2011 by Terry Lovejoy using a 20 cm Schmidt–Cassegrain telescope and a QHY9 CCD camera. It was the third comet discovered by Lovejoy, who reported it as 'a rapidly moving fuzzy object' of 13th magnitude. Independent confirmation came on 1 December from Alan Gilmore and Pamela Kilmartin at Mount John University Observatory in New Zealand, and the comet's existence was announced by the Minor Planet Center on 2 December. It was the first Kreutz-group comet discovered by ground-based observation in 40 years.

The comet reached perihelion on 16 December 2011 at 00:17 UTC, passing approximately 140,000 km above the Sun's surface at 536 km/s. Despite extreme coronal temperatures exceeding one million kelvins and an exposure time of nearly an hour, the Solar Dynamics Observatory and other spacecraft observed the comet emerge from the corona intact. Before perihelion, the nucleus was estimated at 100–200 meters in diameter; after survival, it was thought to be larger, perhaps up to 500 meters. A small companion comet, SOHO-2203, was detected in SOHO images on 14 December and is believed to be a fragment that broke away decades earlier.

Post-perihelion, the comet underwent significant changes. Images on 20 December showed the nucleus had become bar-shaped with a bright tail ray. Some observers could not locate a distinct nucleus, and analysis by Zdeněk Sekanina and Paul Chodas determined that following a dust outburst on 19 December, the nucleus underwent a 'cataclysmic fragmentation' event on 20 December and completely disappeared. If any portion survived, the comet's orbit avoids significant planetary perturbation, with an estimated 622-year orbit and a possible return around the year 2633.

Reader's Guide

Comet Lovejoy's significance lies in its remarkable survival of a close passage through the Sun's corona, an event that was not expected to leave the comet intact. It was the brightest sungrazing comet ever observed by the SOHO spacecraft, reaching an apparent magnitude between –3 and –4, comparable to Venus, though largely invisible to the naked eye at peak due to its proximity to the Sun. It was retroactively dubbed the Great Comet of 2011, and also nicknamed 'The Great Birthday Comet of 2011' and 'The Great Christmas Comet of 2011' due to its announcement on the 16th anniversary of SOHO's launch and its visibility during the Christmas holiday. The comet was observed by eighteen instruments on six satellites (STEREO-A and -B, SOHO, SDO, Hinode, and PROBA2). Its post-perihelion fragmentation history, as analyzed by Sekanina and Chodas, suggests it is a fragment of an unrecorded sungrazer that reached perihelion around 1329, with a parent comet possibly observed in 467 CE. This fragmentation chain implies that other similar fragments may return as sungrazers in the near future. The comet's survival and subsequent disintegration provided valuable data on the physical properties of cometary nuclei and the extreme conditions near the Sun.

Did You Know?

• It reached a speed of 536 km/s at perihelion, about 0.18% the speed of light.
• Analysis suggests the nucleus underwent a 'cataclysmic fragmentation' event on 20 December 2011 and completely disappeared.