Rosetta’s grand finale – probing Comet 67P’s pits

At the end of the month, the Rosetta spacecraft, which has been keeping Comet 67P/Churyumov-Gerasimenko company for the past two years, will crash into its companion near a region of pits that spray dusty jets and end the mission.

On 29 September, Rosetta will be ordered to start its collision manoeuvre, dropping onto a pitted area called Ma’at on the head of the rubber-ducky-shaped comet. 

Its target point is beside a 130-metre-wide pit informally called Deir el-Medina (after an Egyptian town home to a pit filled with archaeological artefacts) taking the measurements all the while – until it crashes around 10.40 UTC on 30 September and we lose contact for good.

Why Ma-at? The pits’ walls are studded with metre-sized lumps nicknamed goosebumps which planetary scientists think might be cometesimals – chunks of material that stuck together in the early days of the solar system.

Despite the simple-sounding final task – dropping on the comet – it’s going to be tricky.  

Operators will need to adjust the precise timing and duration of the final manoeuvre burns, the distance from the comet at that time, the non-uniform gravity of the comet and any effects on Roestta of material streaming from the comet.

A multitude of different trajectories has been calculated taking these variations into account, each resulting in a different touchdown point. But estimates predict that the spacecraft will crash within an ellipse, 700 metres by 500 metres, centred on the target point.

And while the spacecraft managed to find and snap a photo of the Philae probe last week, wedged in a crack on the comet’s small lobe, the pair won’t be reunited. The crash landing site, while on the small lobe, is on the other side.