September 15, 2008--Some scientists believe that our galaxy contains a disk of mysterious dark matter, as suggested by the red contours in this composite image of the Milky Way released this week.

Dark matter may comprise one-fifth of the universe's mass. It is invisible but can be detected by the gravity it exerts on nearby objects.

If such a disk exists, it could allow scientists to directly detect dark matter particles--and perhaps even locate them on Earth.