Smallest exoplanet with a watery atmosphere

Ars Technica : Water vapor has been detected in the atmosphere of HAT-P-11b, an exoplanet about the size of Neptune. Until now, such detection had only been possible in the atmospheres of Jupiter-sized planets. The discovery was made from studying spectrographic data gathered by three spacecraft—the Hubble Space Telescope, the Spitzer Space Telescope, and Kepler. The lack of cloud cover around HAT-P-11b is what allowed researchers to study the spectrum of light that traveled through the planet’s atmosphere as it passed in front of its host star. Because different types of molecules absorb different wavelengths of light, the researchers were able to detect the presence of not only water vapor in the planet’s atmosphere but also hydrogen and small amounts of heavier elements. The ability to determine planets’ atmospheres, in addition to their mass and radii, could provide key insights into planetary formation and evolution. As higher-precision instruments, such as the James Webb Space Telescope, are developed, astronomers hope to be able to detect much fainter signals and even smaller planets.