Spacewatch: Countdown to Philae’s comet landing

The European Space Agency’s Rosetta probe is returning stunning views of the 4km-wide nucleus of comet Churyumov-Gerasimenko from an orbital distance of 10km. These include details of the selected landing site of its Philae lander, riding piggyback on Rosetta. In the meantime, jets of gas and dust are spewing from the neck region of the nucleus’ famous rubber-duck shape. The landing site sits on the crown of the duck’s head.

On 31 October, Rosetta should soar into a more eccentric path before further manoeuvres take it closer again to release Philae at 08:35 GMT on 12 November while 22.5km from the comet. Philae will then fall slowly, snapping images of Rosetta and the surface on the way. If all goes well, it will set down on tripod legs at its target site at about 16:00 GMT, firing a tethered harpoon to anchor it down.

As Philae completes a 360° panorama, its other instruments come into play. Indeed some, measuring the magnetic field, plasma and dust, should have been active already during the descent. Others, on the soles of the tripod legs, will use sonar to investigate the subsurface and seismographs to listen for comet-quakes and dust and rocks tumbling back on to the surface.

Several permittivity probes are tuned, in particular, to reveal how the water content varies up to a depth of 2 metres. A dust impact monitor will also count the number, masses, and rough directions of dust particles hitting Philae as the nucleus rotates every 12.4 hours and becomes more active with its decreasing distance from the Sun.