After 31 months in deep-space hibernation, the Rosetta spacecraft is due to awaken again at 10:00 GMT on Monday, 20 January. When its internal alarm goes off, the European Space Agency's mission will find itself close to the orbit of Jupiter and chasing inwards in the wake of Comet Churyumov-Gerasimenko. A manoeuvre in May should put it on course to enter orbit around the comet in August.
Launched from Kourou in French Guiana in 2004, the 3-tonne craft has already flown by the Earth three times, and Mars once, as its orbit was boosted to converge with that of the comet. On the way, it also returned fly-by images of the asteroids Steins and Lutetia.
Comet Churyumov-Gerasimenko was discovered in 1969 and takes 6.45 years to orbit the Sun, its distance varying between 186 million and 850 million km. It is due to reach perihelion, 37 million km beyond Earth's orbit, on 13 August 2015. Studies using Hubble in 2003 suggest that its nucleus measures perhaps 3km by 5km, like a giant icy rugby ball.
From August, Rosetta should have a grandstand view as the Sun's heat causes the nucleus' ices to sublimate, releasing gas and dust to form the comet's characteristic coma and tail. An early objective will be to pinpoint a likely landing site for Rosetta's 100kg lander, Philae. The mission calls for this to make the first gentle touchdown on a comet in November. Rosetta and Philae should then monitor the comet's composition and evolution through perihelion until the nominal end of the mission in December 2015.