Astronomers have found lots of water in the atmosphere of a Neptune-sized exoplanet — a planet far outside of our Solar System.
It’s just one of a handful of times that scientists have been able to detect water in the atmosphere of an Neptune-sized exoplanet.
The astronomers are using these measurements to piece together how this world may have formed.
The study, combining observations from NASA’s Hubble and Spitzer space telescopes, shows that the distant planet HAT- P-26b has a primitive atmosphere composed almost entirely of hydrogen and helium.
Located about 437 light-years away, HAT-P-26b orbits a star roughly twice as old as our Sun.
The analysis is one of the most detailed studies to date of a “warm Neptune,” or a planet that is Neptune-sized and close to its star.
The researchers determined that HAT-P-26b’s atmosphere is relatively clear of clouds and has a strong water signature, although the planet is not a water world. This is the best measurement of water to date on an exoplanet of this size.
Compared to Neptune and Uranus, the planets in our solar system with about the same mass, HAT-P-26b likely formed either closer to its host star or later in the development of its planetary system, or both.
Researchers were also able to use the water signature to estimate HAT-P-26b’s metallicity – an indication of how rich the planet is in all elements heavier than hydrogen and helium.
It gives more clues about how a planet formed. They determined its metallicity is only about 4.8 times that of the Sun.