Comets Panstarrs & ISONS

Comets

Comets are bodies of rock dust, and ice that exhibit a coma (or atmosphere) and orbit the Sun extending away from the Sun as a tail when they are near to the Sun. Observable comets are occasionally scattered into the inner Solar System by the gravitational fields of nearby stars and giant molecular clouds. There are about 50 known periodic comets in the 'Jupiter' family whose aphelion distance is near Jupiter's, their orbits having been affected by gravitational interactions with that planet. These are potential targets for spacecraft missions, and represent the most primitive material, dating back to the origin of the Solar System. International Cometary Explorer encountered Comet Giacobini-Zinner in 1985, and a small 'armada' of spacecraft (Sakigake and Suisei, VEGA 1 and 2, Giotto) encountered Halley's comet in 1986. In 2004, the Stardust probe captured particles from Comet Wild 2 and is expected to return to Earth in Jan 2006. (Science.nasa.gov)

In 2004 NASA's Stardust mission, controlled from the Jet Propulsion Laboratory in Pasadena, California, collected samples of comet dust for the first time. The stardust probe passed within 240 km/150 mi of the nucleus of Comet Wild 2 and collected samples of comet dust using a lightweight glass foam mesh. The probe also obtained the highest-resolution pictures ever taken of a comet. (Chapman, 33-39)

In July 2005, Scientists effectively launched an exploration into the core of comet Tempel 1. The 372 kg/820 lb probe launched by the NASA Deep Impact mission spacecraft recorded high-resolution images of the impact. The 37,000 kmph/23,000 mph collision took place 133 million km/83 million mi from Earth. Comets are thought to be unchanged since the formation of the Solar System and obtaining information from a comet's interior should provide new insight on the original composition of the Solar System. (Chapman, 2004)

The majority of comets observed from Earth have perihelions near the Earth. This is simply due to observational selection. The brightness of a comet is proportional to 1/rnd2, where r is the remoteness between the comet and the Sun and d is the comet-Earth space. The power n is on average 4.2 but can vary widely around this value. On average a comet passes perihelion about 1000 times before decaying away. Cometary decay produces meteoroid streams.

Comets are named after their discoverers. In any year, say 1994, comets are designated 1994a, 1994b, etc., in order of discovery. Permanent designations 1994 I, 1994 II, ...