Astronomers using NASA’s Hubble Space Telescope observed the smallest exoplanet where water vapor has been detected in the atmosphere.

At only approximately twice Earth’s diameter, the planet GJ 9827d could be an example of potential planets with water-rich atmospheres elsewhere in our galaxy. However, it remains too early to tell whether Hubble spectroscopically measured a small amount of water vapor in a puffy hydrogen-rich atmosphere, or if the planet’s atmosphere is mostly made of water, left behind after a primeval hydrogen/helium atmosphere evaporated under stellar radiation. If the planet has a residual water-rich atmosphere, then it must have formed farther away from its host star, where the temperature is cold and water is available in the form of ice, than its present location. In this scenario, the planet would have then migrated closer to the star and received more radiation. The hydrogen was heated and escaped, or is still in the process of escaping the planet’s weak gravity. The alternative theory is that the planet formed close to the hot star, with a trace of water in its atmosphere. The Hubble program observed the planet during 11 transits – events in which the planet crossed in front of its star – that were spaced out over three years. During transits, starlight is filtered through the planet’s atmosphere and has the spectral fingerprint of water molecules. If there are clouds on the planet, they are low enough in the atmosphere so that they don’t completely hide Hubble’s view of the atmosphere, and Hubble is able to probe water vapor above the clouds. GJ 9827d was discovered by NASA’s Kepler Space Telescope in 2017. It completes an orbit around a red dwarf star every 6.2 days. The star, GJ 9827, lies 97 light-years from Earth in the constellation Pisces.

Hubble has found water on a small rocky planet beyond our Solar System

Nu voor het eerst ook waterdamp gevonden in de atmosfeer van een kleine planeet