Big, gaseous planets are becoming a commonplace finding in our galaxy, but until now astronomers had never detected a body as small as our Earth orbiting another star. Two new planets announced today matter in the search for life because they are small enough to have a solid surface. They are too close to their sun to have liquid water, but astronomers are optimistic that more habitable worlds will be found soon.
On Tuesday I caught up with Villanova astronomer Andrej Prsa, who was part of the team announcing the planets. They were detected with a space telescope called Kepler, launched in 2009 with the express goal of finding other earths.
Prsa's job is to make sure Kepler is detecting real planets and not reacting to false alarms. The astronomers don't actually see any of these planets but indirectly detect their presence by monitoring stars for tiny periodic dips in brightness. These dips are indications that planets are passing in front and creating mini-eclipses. (The image is an artist's reconstruction)
The newly announced planets only dim the stars by 100 parts per million, said Prsa, but measuring such minuscule changes is within Kepler's ability. The project has led to announcements of hundreds of "candidate planets," he said, but astronomers have high standards of evidence when it comes to naming a true discovery.
To tell which candidates are real, the astronomers watch them for a few orbits to make sure the dimming really is periodic. And they have to rule out the possibility that they're seeing the effects of a series of stars eclipsing each other.
That means the easiest planets to pin down are ones that orbit fast. The new planets, called Kepler 20e and Kepler 20f, orbit every 6.1 days and 19.6 days. They are 1000 light years away. With its much longer orbit, a distant twin to Earth would have to be watched for more than three years.