NASA astronomers found evidence of clear skies and water vapor on a super-small gaseous exoplanet.
The planet is about the size of Neptune and is the smallest from which molecules have been detected.
"This discovery is a significant milepost on the road to eventually analyzing the atmospheric composition of smaller, rocky planets more like Earth," said John Grunsfeld, assistant administrator of NASA's Science Mission Directorate. "Such achievements are only possible today with the combined capabilities of these unique and powerful observatories."
The planet's cloudless skies allowed researchers to get a good luck at its underlying molecules and gain insight into its composition. The researchers hope to find more planets of the same size that have similar crystal-clear visibility.
"When astronomers go observing at night with telescopes, they say 'clear skies' to mean good luck," said Jonathan Fraine of the University of Maryland, College Park, lead author of a new study appearing in Nature. "In this case, we found clear skies on a distant planet. That's lucky for us because it means clouds didn't block our view of water molecules."
The planet is classified as an exo-Neptune and dubbed HAT-P-11b, it orbits the star HAT-P-11 once every five days. It is believed to have a rocky core and gaseous atmosphere and is located about 120 light-years away in the constellation Cygnus. Planets such as exo-Neptunes are extremely hard to study because of their small size. While water vapor has been detected on larger Jupiter-sized planets, this is the first times it has been spotted on such a small object.
To make their findings the researchers looked at data from the NASA Hubble, Spitzer and Kepler telescopes. They employed a technique called transmission spectroscopy, in which a planet is observed when it crosses in front of its host star. If water vapor is present on the planet it will absorb starlight, leaving behind light signatures that can be spotted through a telescope.
The researchers observed water vapor on the planet, but needed to make sure it was not actually caused by cool spots on the faces of stars. Kepler and Spitzer data revealed the star spots were too hot to emit steam, indicating the water was indeed from HAT-P-11b.
"We think that exo-Neptunes may have diverse compositions, which reflect their formation histories," said study co-author Heather Knutson of the California Institute of Technology. "Now with data like these, we can begin to piece together a narrative for the origin of these distant worlds."
The researchers hope to examine more exo-Neptunes in the future, and hope the next ones they look at will also be clear-skied.
"The work we are doing now is important for future studies of super-Earths and even smaller planets, because we want to be able to pick out in advance the planets with clear atmospheres that will let us detect molecules," Knutson said.
