Layered terrains on Mars discovered just last year by NASA's Mars Global Surveyor spacecraft bear a striking resemblance to sedimentary deposits here on Earth that form under water. Liquid water is scare on Mars nowadays, but it might have been common four billion years ago. Studying Mars's sedimentary deposits, if that's what they are, could tell scientists if water existed on Mars long enough for primitive life to begin. Indeed, the layered rocks themselves may be the best places to go fossil hunting. No object except for a black hole can have an event horizon, so evidence for its existence offers resounding proof of black holes in space.
Gravity draws gas from a companion star onto a black hole in a swirling pattern.
As the gas nears the event horizon, a strong gravitational red shift makes it appear redder and dimmer. By comparing the energy output of different types of X-ray novae while they were inactive, the Chandra team determined that systems suspected of harboring black holes emitted only one percent as much energy as systems with neutron stars.