10th Planet (Jan. 2006)

A stunning discovery at the far reaches of our solar system raises questions about what makes a planet a planet. Watch now (5 mins.)

Asteroid (Oct. 2006)

Will a doomsday rock the size of the Rose Bowl hit Earth in 2036? Watch now (12 mins.)

Dark Matter (June 2008)

Turns out most of the universe is held together by a mysterious, invisible substance. Watch now (14 mins.)

Phoenix Mars Lander (July 2008)

NASA's latest robot has already found frozen water and is looking for more signs that the Red Planet could support life. Watch now (12 mins.)

Saving Hubble (July 2008)

Two teams of spacewalkers take on the risky mission of reviving the ailing Space Telescope. Watch now (13 mins.)

The Search for ET (July 2008)

Astronomers have their radio telescopes tuned to receive signals from alien worlds. But is anybody out there? Watch now (11 mins.)

Space Elevator (Jan. 2007)

Can we build a 22,000-mile-high cable to transport cargo and people into space? Watch now (13 mins.)

Space Storms (July 2008)

Behind the dazzling display of the aurora borealis are space storms that could turn the lights off here on Earth. Watch now (10 mins.)