08:24 UK time, Friday, 17 October 2014
One of the fascinating things about comets is their blackness - akin to a lump of coal or the briquettes you put on the BBQ.
The Atlantis shuttle lands at the Kennedy Space Center in Florida, bringing a close to Nasa's 30-year orbiter programme.
135 missions 33 for Atlantis
355 astronauts taken into space since 1981
The fleet has flown well over 870 000 000 km
The shuttle and its boosters have 2.5 million moving parts
'The shuttle made possible the permanent presence of humans in space'
We detail five of the possible successors to the shuttle
The Challenger disaster was both a tragedy and profoundly shocking
How space fans are blogging farewell to an era
Newsnight's Science editor Susan Watts visits the world's first fully commercial spaceport
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