Needle in a Haystack

Just how difficult is it to discover a planet moving around another star? The Kepler space telescope finds planets by observing the brightness of stars over long periods. If a planet passes in front of its star, the light will dim slightly. But it doesn’t dim very much, so it takes some serious data analysis to discover.

You can get an idea of this challenge in the image below. It is an image of discovered planets plotted as shadows on the star they orbit. We don’t observe the stars as disks like this, only as points of light, but you can see that larger planets are easier to see than smaller ones. How many planets can you see in the image?

Oh, and that one star all by itself? That is the Sun in comparison to the other stars. You can see the shadow of Jupiter pretty clearly, but can you see Earth as well?

Jason Rowe, Kepler Mission