NASA’s Kepler space telescope, which searches for exoplanets via a technique known as the transit method, looked closer to home and observed Neptune when the planet entered its field of view between November 2014 and January 2015.
By measuring small changes in Neptune’s brightness with Kepler and comparing the changes with images taken by the Hubble Space Telescope, scientists gained insight into similar changes seen in exoplanets, which cannot be directly observed because they are so far away.
Using the transit method, scientists look for dips in a star’s light caused by an orbiting planet passing in front of the star. The method has been successfully utilized to discover numerous exoplanets.
When Neptune entered its field of view, Kepler studied its rotation, movement of clouds in its atmosphere, and tiny changes in the Sun’s brightness.
The telescope also measured the amount of sunlight reflected off Neptune and its two largest moons, Triton and Nereid.
Kepler found variations of less than one percent in Neptune’s brightness. Direct observations of Neptune conducted by Hubble at the same time revealed these variations to be caused by clouds reflecting sunlight in the planet’s atmosphere.
“The Kepler observations are unique because they allow us to see the light curve of an object close enough to image and resolve cloud features,” said Amy Simon of NASA’s Goddard Space Flight Center in a public statement.
“These observations prove that rapid variations in light curves of brown dwarfs and exoplanets can be caused by changing clouds.”
Kepler orbits the Sun in an Earth-trailing heliocentric orbit.