A source of speculation since the 19th Century, a new study may reignite the debate about a planet that could be lurking at the edge of our Solar System.
Scientists have previously predicted the existence of a large planet lurking in the farthest reaches of the Solar System. However, no observational evidence for this world has been found to date.
Some researchers think that a hypothetical ninth planet exists in the furthest reaches of the Solar System.
The collective gravity of lots of little objects might add up to a powerful force.
"It will truly be a historical mission to take our first step into interstellar space."
Scientists say an object about the size of Mars is disrupting the orbits of Kuiper Belt objects.