Small rocky planets formed throughout the history of the universe
Tiago Campante/Peter Devine
Some planets were already billions of years old when Earth was a mere twinkle in our sun’s eye.
The Kepler space telescope has unearthed the oldest known solar system. Five tiny rocky worlds snuggle up to the 11.2-billion-year-old Kepler 444, a cool red star more than twice as old as our sun. Because planets form at the same time as the stars they orbit, the discovery implies that the universe has been churning out rocky planets throughout its entire history, providing ample time for alien life to develop and perhaps flourish (SN: 2/7/15, p. 7).
Kepler 444 itself, however, is not the best place for life to get going. The star’s planets, all between the sizes of Mercury and Earth, are too close to it for liquid water to endure on their surfaces. The longest year for any of the planets is less than 10 days long, astronomers