"A team of astronomers has identified a novel
new kind of galactic wanderer - lone, Jupiter-sized
planets expelled from forming solar systems
and drifting in the empty void between the stars.

The researchers, led by Takahiro Sumi of Japan's
Osaka University, spotted 10 such free-floating
"orphan planets" in data from a 2006-7
microlensing survey of our galaxy's centre, which
searched for the tell-tale sign of transiting bodies'
gravitational fields distorting light from distant
stars.

Team member David Bennett, of the University of
Notre Dame in Indiana, explained that this first
sighting in a small portion of the Milky Way
points to enormous numbers of orphans. He
said: "Our survey is like a population census.
We sampled a portion of the galaxy, and based
on these data, can estimate overall numbers in
the galaxy.""

See:

http://www.theregister.co.uk/2011/05/19/orphan_planets/