Comet 67P/Churyumov Gerasimenko is a celestial object coming from the Kuiper-Edgeworth Belt, a ring-shaped region in the Solar System located beyond the orbit of Neptune. 67P orbits the Sun along an elliptical path between Earth and Jupiter, and is therefore considered to be a member of the Jupiter family.
The Hubble Space Telescope delivered the first images of the comet nucleus during observations conducted on 12 March 2003 in preparation for the Rosetta mission. The pictures revealed an oval-shaped celestial body measuring three by five kilometres. Its rotation period was determined to be between 12.4 and 12.9 hours, and its mean diameter was identified as roughly four kilometres. One orbit around the Sun is a 6.45-year journey for the comet. Darker than coal, the density of the comet's surface material is comparable with that of a sponge. Images from the OSIRIS camera on board Rosetta, which were acquired at a distance of 14,000 kilometres, show that 67P/Churyumov-Gerasimenko consists of two clearly distinguishable parts. The two components probably collided with one another at low speed during the development of the Solar System 4.5 billion years ago and stuck together.
A turbulent story
Jupiter's gravitational pull has caused the comet's orbit to change radically over the last 200 years. Until 1840, its perihelion distance (the point along its orbit closest to the Sun) was found to be four Astronomical Units (AU), or four times the distance between Earth and the Sun (in total just less than 150 million kilometres). But a close sweep around Jupiter reduced its perihelion distance, which until 1959 was 2.7 AU. A further Jupiter flyby in February 1959 cut the perihelion once more to its current value; its shortest distance to the Sun is 186 million kilometres (1.24 AU), while its farthest (aphelion) is 857 million kilometres (5.68 AU). Estimates suggest that during its perihelion passage in 2002, 67P/Churyumov Gerasimenko released 60 kilograms of dust into space every second, while calculations for the turn of the year 1982/83 indicate quantities of up to 220 kilograms per second.