This digital painting by Erik Viktor shows the European Space Agency Rosetta spacecraft in orbit around Comet Wirtanen in 2011 after a voyage that lasted for 8 years.
Note the small Roland Lander carried piggyback by the larger mother ship.
The mother ship would map and photograph the surface of the comet whilst analysing its surface and distant atmosphere with various scanners.
Rosetta would also act as a relay transmission station whilst the lander is on the surface of the Comet.
The illustration pictures the tiny Roland cometary lander separating from the mother ship - its undercarriage unfolded-  and preparing to approach and land on the rough surface of the tumbling comet.

Comets are among the oldest bodies in the solar system. Although most remain in the Oorst cloud at the boundary of the Solar system, some are swung towards the Sun by a combination of various gravity forces within the Galaxy.
Comets, also called “dirty snowballs” are believed to be highly volatile, made out of a mixture of various types of ice, dust and rocks.
When a cometary wanderer approaches the Sun the solar radiation and heat evaporate the volatile elements and dust away from the comet and the Sun and create the highly spectacular and often multiple tails that make comets so typical. This gaseous activity and the resulting geysers tend to act like giant reactors making the comet tumble on its axis.
Until recently Asteroids, albeit similar in shape, where believed to be totally different bodies but new theories suggest that some may in fact be extinct comets that have expended all of their volatile elements.
 

© Erik Viktor/Spaceworld 2000