|  | | | | | | | Comet 46P/Wirtanen
After its brief encounters with Otawara and Siwa, Rosetta will travel far beyond the asteroid belt to reach its main target, Comet Wirtanen. Wirtanen is a large dirty snowball that orbits the Sun once every 5.5 years. During this time, it commutes between the orbits of Jupiter and the Earth. However, little is known about it, despite its regular visits to the inner Solar System.
Most of the time, its faint image is drowned in a sea of stars, making observations with Earthbased telescopes extremely difficult. However, during its short-lived excursions to the inner Solar System, the warmth of the Sun causes ices on its surface to evaporate and jets of gas to blast dust grains the surrounding space. Unfortunately, although this enveloping 'coma' of dust and gas increases Wirtanen's
brightness, it also completely hides the comet's nucleus.
Rosetta's task is to rendezvous with the comet while it still lingers in the cold regions of the Solar System and shows no surface activity. After releasing a Lander onto the dormant nucleus, the Orbiter will chase Wirtanen as it charges headlong towards the inner Solar System at speeds of up to 135 000 km/h.
| Comet 46P/Wirtanen | | | Diameter of nucleus – estimated (km) | 1.2 | | Orbital period (years) | 5.45 | | Minimum distance from Sun (million km) | 159 | | Maximum distance from Sun (million km) | 768 | | Orbital eccentricity | 0.657 | | Orbital inclination (degrees) | 11.72 | | Year of discovery | 1948 | | Discoverer | Carl Wirtanen
(Lick Observatory, USA) |
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Over an entire year, as it approaches the Sun, Rosetta will orbit the comet, mapping its surface and studying changes in its activity. As its ices evaporate, instruments onboard the Orbiter will study the dust and gas particles that surround the comet and trail behind it as streaming tails, as well as their interaction with the solar wind.
| | Last update: 13 December 2002 |  |
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