The American Deep Impact spacecraft has caught first sight of its quarry.
Comet Tempel 1 viewed on 25 April
The probe has returned an image of Comet Tempel 1, taken from a distance of 64 million km (40 million miles).
The observation will help Deep Impact's navigators, engineers and scientists as they tweak its flight path for a close rendezvous on 4 July.
The probe will eject a 372kg impactor into the path of the comet to blast a deep hole in it - to learn more about how these objects are put together.
Comets are the "undercooked leftovers" that remained when a sprawling cloud of dust and gas condensed to form the Sun and planets 4.6 billion years ago.
Scientists hope the mission will answer basic questions about how the Solar System came to be, by offering a better look at the nature and composition of these frozen balls of ice, dust and rock.
Deep Impact will punch a crater in Comet Tempel 1
"It is great to get a first glimpse [of] the comet from our spacecraft," said Deep Impact Principal Investigator Dr Michael A'Hearn, of the University of Maryland, US.
"With daily observations beginning in May, Tempel 1 will become noticeably more impressive as we continue to close the gap between spacecraft and comet.
"What is now little more than a few pixels across will evolve by 4 July into the best, most detailed images of a comet ever taken."