Rosetta: Catching a comet
Sen—Rosetta has spent ten long years chasing down Comet 67P/Churyumov-Gerasimenko and, after a journey of more than ten years and six billion kilometres, she is on the brink of launching one of the most audacious missions ever attempted: to land a probe, called Philae, onto the surface of a comet.
The comet, a 3.5 kilometer-wide lump of rock and ice (shaped a little like a giant rubber duck), is currently barreling through space (tumbling head-over-heals as it goes) at some 135,000km/h—making any attempted landing hazardous to say the least.
To make matters worse, the lander (a roughly cuboid device, about the size of a washing machine) will have to make the seven-hour descent to the comet’s surface without any ability to steer itself, or communicate with its mission controllers on Earth, 510 million kilometres away.
Philae’s target will be a one square kilometre region of the comet’s surface, named Agilkia. Although the landing site is relatively boulder-free, mission controllers admit that there is a 20 per cent chance that Philae will strike a boulder or fall down a slope, potentially leaving it unable to transmit signals back to Rosetta. There is also a chance that the surface could be covered in a deep layer of dust that might cover the lander’s instruments and solar panels.
As if that wasn’t bad enough, although the comet is quite massive (weighing in at some ten billion tonnes), its gravity is extremely weak, meaning that Philae could just bounce back off into space. To prevent this, the lander is equipped with ice screws and harpoons that will be deployed on touch-down to anchor the craft to the surface.
If Philae does land successfully, it will begin science operations immediately, deploying its veritable Swiss Army Knife-like array of instruments in an attempt to learn more about this enigmatic icy traveller.