22P/Kopff

Lore & Background

22P/Kopff was discovered when August Kopff analyzed photographic plates exposed on 20 August 1903, comparing them with pre-discovery images of the same region. On 23 August 1903, he concluded it was a comet with an estimated apparent magnitude of 11. In mid-September 1906, a team headed by Kiel Ebell of the Berkeley Astronomical Department recognized its short-period nature. The comet was missed on its return of 25 November 1912, but was recovered on 25 June 1919, less than three days from the predicted position. Close approaches to Jupiter in 1938 and 1943 decreased the perihelion distance and orbital period, leading to a notable brightening in 1945 when the comet peaked at magnitude 8.5. The 1951 return was unusual: the comet was 3 magnitudes fainter than expected when recovered in April, yet still reached magnitude 10.5 in October. A very close pass to Jupiter in 1954 increased the perihelion distance to 1.52 AU and the orbital period to 6.31 years. On 30 November 1994, Carl W. Hergenrother recovered the comet at a stellar magnitude of 22.8 using the 1.5-m reflector at the Catalina Sky Survey; it reached magnitude 7 during the 1996 perihelion passage. The nucleus is estimated to be 3 km in diameter with an albedo of 0.05, and its dark surface is due to hydrocarbons converted to a tarry substance by solar ultraviolet radiation.

Reader's Guide

22P/Kopff was the planned target for the joint NASA/ESA Comet Rendezvous Asteroid Flyby (CRAF) mission, a Mariner Mark II spacecraft that would have launched in February 1996. After a flyby of Earth and 449 Hamburga, CRAF would have reached the comet by August 2001 and studied it for two years. The mission was developed in tandem with Cassini–Huygens but was cancelled in 1992 due to cost overruns. In 2000, a comet orbiter named Odyssey was proposed for NASA's Discovery Program to rendezvous and orbit 22P/Kopff by September 2009, launching from a Delta II rocket in June 2006; it was not selected in favor of Dawn and Kepler. The comet's orbit continues to evolve: it will pass 0.439 AU from Jupiter on 25 April 2026, then come to perihelion on 28 June 2028 at 1.32 AU from the Sun, and pass 0.353 AU from Earth on 13 July 2028. Its dark nucleus and history of orbital perturbations make it a subject of ongoing interest.

Did You Know?

• 22P/Kopff was discovered on photographic plates exposed on 20 August 1903, but not identified as a comet until 23 August 1906.
• The comet was missed on its 1912 return but recovered in 1919 less than three days from the predicted position.
• Close approaches to Jupiter in 1938 and 1943 decreased the comet's perihelion distance and orbital period.
• 22P/Kopff was the planned target of the cancelled NASA/ESA CRAF mission.