The decision to try to land a robot on Comet 67P/Churyumov-Gerasimenko on 12 November has been confirmed. Last month, planners on Europe’s Rosetta mission announced a preference for a touch-down location on the head of the icy, rubber-duck-shaped object.
A detailed follow-up analysis, informed by new high-resolution pictures, has found no reason to rescind the choice. The Rosetta probe will eject the Philae robot shortly after 08:30 GMT on the day of landing. The shove will be imparted at a distance of about 20km from the surface of 67P.
The descent to the 4km-wide comet is expected to take about seven hours. Success or failure will be known roughly 30 minutes after that. This additional period is the length of time a radio signal takes to travel 509 million km – the separation between 67P and Earth in mid-November.
Final confirmation of the touchdown sequence and location was given by the Lander Operations Readiness Review, which met at the European Space Agency’s mission control in Darmstadt, Germany, on Tuesday.
“Now that we know where we are definitely aiming for, we are an important step closer to carrying out this exciting – but high-risk – operation,” said Fred Jansen, Esa’s Rosetta mission manager, in a statement.
“However, there are still a number of key milestones to complete before we can give the final ‘go’ for landing.”
Rosetta is currently manoeuvring itself into a circular 10km-high orbit around the comet. This will permit even more detailed pictures of the landing zone – known at present simply as Site J – to be acquired. This may give controllers some additional information as they approach the hazardous venture ahead.
On 28 October, Rosetta will be commanded to start “phasing” its orbit ready for landing.
This involves, in the first instance, raising its altitude to 30km.
On the day of landing, the probe will essentially dive-bomb the comet, to be sure of putting Philae on exactly the right path to contact the middle of Site J. Then, shortly after release, Rosetta will perform a sharp turn, taking itself away from 67P and on to a trajectory that allows it to maintain permanent radio contact with the robot lander.
The rest will be down to physics – and a large slice of luck. To succeed, Philae will have to miss some sizeable cliffs and boulders.
Little is known about the composition and strength of the comet’s surface layers, and the fear is that the robot could simply bounce off 67P in what will be a very low-gravity environment. Foot-screws and harpoons will be deployed at the moment of touchdown to try to ensure that does not happen.
Tuesday’s confirmation sets in train a sequence of decision points that will each require a “go/no-go” from Darmstadt’s controllers. If at any of these key moments, the mission team is unhappy with progress, or with the status of Rosetta and Philae, it can call a “hold” in the timeline.
The sequence to touchdown would then be revised depending on the resolution of any problem.
- •Named after its 1969 discoverers Klim Churyumov and Svetlana Gerasimenko
- •Referred to as a “Jupiter class” comet that takes 6.45 years to go around the Sun
- •It gets as close as 180 million km from our star, and as distant as 840 million km
- •The icy core, or nucleus, is about 4km across and takes 12.4 hours to rotate
- •Rosetta has measured 67P to have a mass of roughly 10 billion tonnes
- •Its volume is 25 cu km, giving it a bulk density of 0.4g/cc – similar to some woods