2. Sun Existing for about 4 and a half billion years, it has burnt up about half of the hydrogen in its core. This leaves the Sun's life expectancy to 5 billion more years, at which time, the Sun's elements will "swell" up, swallow Earth, and eventually die off into a small white dwarf. ( Professor Stephen Lawrence, Columbia University )
3. Mercury Mercury speeds around the Sun in a wildly elliptical (non-circular) orbit that takes it as close as 47 million km and as far as 70 million km from the Sun. The planet completes a trip around the Sun every 88 days, speeding through space at nearly 50 km per second, faster than any other planet. (About.com)
