Rosetta finds oxygen on comet 67P in 'most surprising discovery to date'

To be clear, the mass doesn't change, but the gravitational force is equivalent to that on a 1 gram mass on Earth.

Philae's gas rocket was jammed, the wax seal had frozen or the sensor had broken. The pilots wanted an extra day to get it working but they were told the fanfare had begun and the various Presidents couldn't be disappointed so they had to launch.

Therefore they had to throw the Philae 'paperclip' exactly right using only Rosetta's thrusters to toss it toward the comet - no retrorocket to damp landing, only math.

Calculations were further complicated by 67P's dual lobed masses with Lagrange points inbetween the two lobes and an low escape velocity of 0.5 metres / second - practically a 3-body problem. Dr Matt Taylor is an awesome pilot.

Add to this the unexpected surface density (hard ice-crete shell rather than powdery floof) so the harpoon and leg screws would be worse than useless - it was an incredible piece of spaceship trajectory design and luck.

Thankfully the anchoring harpoon failed to fire, it would likely have ejected Philae from the comet.

The extreme reluctance of the OSIRIS team to share high resolution images of the surface may have complicated the search for Philae ( for which they were rightly but ineffectively chastised by the head of ESA ).

As the mission nears its close Rosetta will land on the comet and so post-perihelion close views across the surface will become available.

The 6 CIVAS photos returned from the surface of 67P by Philae IMHO rank alongside Armstrong's lunar footprint as humanity's greatest artworks.