The Solar System: The Kuiper Belt and Oort Cloud

Our solar system is a vast place, with lots of mostly empty space between planets but out there are comets, asteroids and more rocky, frozen objects (including dwarf planets) yet to be discovered in the Kuiper Belt and Oort Cloud.

CREDIT: NASA

NASA's Spirit Rover landed on Mars nine years ago today (Jan. 3), kicking off a surface mission that's still operational thanks to the amazing endurance of Spirit's twin Opportunity.

Mars is currently host to five active space missions, commanding more attention than any planet apart from Earth. But unmanned probes are also exploring many other solar system bodies, from the sun out to Pluto and beyond.



Solar Terrestrial Relations Observatory: NASA's $550 million sun-studying STEREO mission, which blasted off in October 2006, consists of two spacecraft, known as A and B. Both probes are in a heliocentric orbit, with A zipping around the sun faster than Earth and B lagging somewhat behind.