Alan Pickup tracks the European Space Agency craft as it pursues its icy target on a headlong dive into the Sun
The European Space Agency’s Rosetta spacecraft, which awoke in January from 31 months of hibernation, sighted its target, Comet Churyumov–Gerasimenko, in March and soon glimpsed signs that the comet, too, is reawakening as it plunges closer to the Sun.
By May, the comet’s icy nucleus, only some 4km wide, was surrounded by a coma of dust extending 1,300km into space – clearly material ejected from the nucleus as it began to feel the Sun’s warmth. Surprisingly, the coma had disappeared by early June, suggesting that its development into a fully-fledged comet may be erratic. At the same time, but reported only this week, Rosetta’s microwave spectrometer detected water vapour escaping from the nucleus.
Meanwhile Rosetta began a series of manoeuvres in May that by 2 July should take it 94% of the way to matching its velocity to that of the comet, currently some 570m km from the Sun. A further five minor manoeuvres should end on 6 August with Rosetta 100km from the nucleus and ready to creep even closer.
As the pair dive Sunwards, eventually to reach perihelion 186m km from the Sun a year later, Rosetta could not be better placed to monitor the nucleus, its dust emissions, and how the rates of production of water, and the expected carbon monoxide, methanol and ammonia, change with time.
With results from Philae, a small lander carried by Rosetta but due to touch down on the nucleus in November, the mission should yield vital insights into the origin and makeup of comets.
[Image: Rosetta fly-by near a comet. Frame from the movie "Chasing A Comet – The Rosetta Mission," via Wikipedia Commons]