Using the space telescope Hubble by NASA and ESA, astronomers have observed the smallest exoplanet, where water vapor has been detected in its atmosphere.

Hubble observed the planet GJ 9827d during eleven transits in which the planet passed in front of its star over a period of three years. The planet completes an orbit around a red dwarf star every 6.2 days. The star GJ 9827 is located 97 light-years from Earth in the constellation Pisces.

At about twice the diameter of Earth, planet GJ 9827d suggests that possible planets with water-rich atmospheres could exist elsewhere in our galaxy.

However, it clarifies that it is too early to tell whether Hubble spectroscopically measured a small amount of water vapor in a hydrogen-rich atmosphere, or whether the planet’s atmosphere is mostly water and was preserved after an initial hydrogen/solar atmosphere evaporated due to stellar radiation .

If the planet has remnants of a water-rich atmosphere, then it must have formed further away from its star, where the temperature is cold and water is available in the form of ice. In this scenario, the planet would have moved closer to the star and received more radiation, and then the hydrogen heated up and escaped, or is still in the process of escaping, the planet’s weak gravity. The alternative theory is that the planet formed near the hot star, with a trace of water in its atmosphere.

Hubble’s discovery opens the door to studying the planet in more detail and makes it a good target for the James Webb Space Telescope to look for other atmospheric molecules with infrared spectroscopy.