Vol. 579
In section 10. Planets and planetary systems

The recent dynamical history of comet 67P/Churyumov-Gerasimenko

In section 11. Celestial mechanics and astrometry

A study of the past dynamics of comet 67P/Churyumov-Gerasimenko with fast Lyapunov indicators

In advance of the A&A special feature on the Rosetta results, two articles analyze the dynamical history of comet 67P/Churyumov-Gerasimenko and provide context to the observations of the comet by the Rosetta spacecraft. The article by Maquet looks at the recent history of the comet and shows that the comet had close approches to Jupiter on October 2, 1923, and on February 4, 1959. The last encounter, with a closest distance to Jupiter of 0.05 au, modified the comet's orbit very significantly, reducing its perihelion distance from about 2.7 au to 1.3 au. Close approaches to the Sun (i.e. within less than 1.5 au) then occurred every 6.4 years. The next close approach on August 13, 2015, will be the ninth since the first in 1963. But because of chaos, the origin of the comet cannot be traced with simple backward integrations to more than about 100 years ago. The article by Guzzo & Lega thus examines the origin of the comet using a probabilistic approach. Although 67P is a Jupiter-family comet (i.e., its orbit is mostly controlled by Jupiter) traditionally thought to originate in the Kuiper belt beyond Neptune, they find that there is a 60% probability that the comet that comes from the Oort cloud. This rules out any firm conclusions, except one: the interplay between observations and theories promises rich discoveries! Stay tuned for further news on 67P!