Newly-found distant 'warm Neptune' has primitive atmosphere

A team of scientists has discovered a distant Neptune-sized planet that has clear skies and an atmosphere almost entirely composed of hydrogen and helium, scientists have discovered.

The study led by NASA with contributions from the University of Maryland revealed that the distant planet HAT-P-26b is located about 437 light years away from Earth and orbits a star roughly twice as old as the sun.

The analysis is one of the most detailed studies to date of a "warm Neptune," a planet that is Neptune-sized and orbits close to its star.

By combining observations from NASA's Hubble and Spitzer space telescopes, 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. The study also provides the best measurement to date of water on an exo-planet of this size.

Co-author Drake Deming said, "Not too long ago, it was exciting just to find an exoplanet. But now, as technology and methods become more refined, we are building a whole new understanding of the wide diversity of planetary systems beyond our own. It's a very exciting time to be in this field."

The discovery of such a primordial atmosphere on this Neptune-sized planet has implications for how scientists think about the birth and development of planetary systems. 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 a combination of both.

"Astronomers have just begun to investigate the atmospheres of these distant Neptune-mass planets, and almost right away, we found an example that goes against the trend in our solar system," said lead author Hannah Wakeford. "This kind of unexpected result is why I really love exploring the atmospheres of alien planets."

"This analysis shows that there is a lot more diversity in the atmospheres of these exoplanets than we were expecting, which is providing insight into how planets can form and evolve differently than in our solar system," said second author David K. Sing. "I would say that has been a theme in the studies of exoplanets: Researchers keep finding surprising diversity."

The study is published in the journal Science.