In a display of interstellar teamwork, NASA’s Hubble, Spitzer and Kepler space telescopes have discovered clear skies and water vapor in the atmosphere of a Neptune-sized planet orbiting a star 120 light years from Earth. According to the space agency, this may not only provide insights into the formation of giant exoplanets, but also act as a new tool for detecting water on Earth-like planets orbiting other stars.
Astronomers like clear skies on Earth, because it makes it easier to look out of the atmosphere. They also like clear skies on other planets because it allows them to look in. Otherwise, they just end up looking at a load of cloud tops. In a very distant example of a nice day, astronomer found clear skies on HAT-P-11b; an exo-Neptune planet that orbits the orange dwarf star HAT-P-11 once every five days.
Located 120 light years distant in the constellation of Cygnus, HAT-P-11b is a hot world with a rocky core and gaseous atmosphere. According to NASA, this is the smallest planet on which any sort of molecules have been detected. Previously, molecules, including water vapor, have been detected in the atmospheres of Jupiter and super-Jupiter sized planets because of their size and less dense atmospheres. But HAT-P-11b is the smallest planet yet where water has been detected – nothing of its size has been within the range of current technology until now.
Artist's concept comparing the atmosphere of exoplanet HAT-P-11b (right) and how other exoplanets seen until now may look (left) (Image: NASA/JPL-Caltech)
The technique used for peeking through the atmosphere is called transmission spectroscopy. This involves studying the light from the planet’s star as it passes through the planet’s atmosphere. Obviously, if that atmosphere is laden with clouds, the light won’t go through. Fortunately, HAT-P-11b’s atmosphere has clear skies in at least the higher altitudes. This clearness was demonstrated by the fact that the Hubble could detect the starlight.
Using the Hubble's Wide Field Camera 3, the team took spectroscope readings of the light passing through the planet’s atmosphere and compared it to that of the star. The differences would indicate the presence and nature of any molecules in the air around HAT-P-11b.
According to NASA, the team did detect water vapor, but water can be found in regions of cooler stars called “starspots,” which are analogous to sunspots. To eliminate the possibility that all they were seeing was water on HAT-P-11, the team used data from the Kepler and Spitzer telescopes. Since they can see in the infrared, they could determine the temperature of the star and concluded that any starspots present would be too hot for water, which would break down into its constituent atoms at too high a temperature.
NASA says that HAT-P-11b has an atmosphere of water vapor, hydrogen, and other gases yet to be determined, and that the data will be helpful in learning more about the diversity of giant exoplanets and their formation. NASA plans to continue working to detect clear skies and water vapor on smaller and smaller planets with the goal of ultimately finding water on an Earth-like exoplanet using the James Webb telescope, which launches in 2018.
"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," says Heather Knutson of the California Institute of Technology in Pasadena.