“A star’s rotation slows down steadily with time, like a top spinning on a table, and can be used as a clock to determine its age,” said astronomer Soren Meibom from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Knowing a star’s age is important for many astronomical studies and, in particular, for planet hunters. With the bountiful harvest from NASA’s Kepler spacecraft (launched in 2009) adding to previous discoveries, astronomers have found nearly 2,000 planets orbiting distant stars. Now, they want to use this new zoo of planets to understand how planetary systems form and evolve and why they are so different from each other.
“Ultimately, we need to know the ages of the stars and their planets to assess whether alien life might have evolved on these distant worlds,” said Meibom. “The older the planet, the more time life has had to get started. Since stars and planets form together at the same time, if we know a star’s age, we know the age of its planets, too.”
Learning a star’s age is relatively easy when it’s in a cluster of hundreds of stars that all formed at the same time. Astronomers have known for decades that if they plot the colors and brightnesses of the stars in a cluster, the pattern they see can be used to tell the cluster’s age. But this technique only works on clusters. For stars not in clusters (including all stars known to have planets), determining the age is more difficult.
