Kepler spacecraft discovers 'invisible world'

[steorra]

Kepler spacecraft discovers 'invisible world'

Kepler normally discovers planets orbiting other stars by observing a star's light dim as a planet passes in front of it. Now it's discovered another one by an interesting indirect method. A star has (at least) two planets. Kepler can detect the first planet in the normal way, by observing changes in the star's light when the planet transits it. The second planet has a gravitational influence on the first planet, and changes the timing of its transits by a few minutes. This change in timing shows us that the second planet is there, even though Kepler can't see it transiting.