Unique “Neptune-like” Exoplanet Found to Contain Water Vapor

Rebecca Jean T.
2 min readMar 15, 2022

New research presented in a series of virtual American Astronomical Society media briefings announces the discovery of a Neptune-like exoplanet orbiting unusually close to its host star. What’s more, this planet has also been found to contain water vapor, making its existence even more puzzling.

Artist concept of TOI-647b. Credit: NASA/JPL-Caltech

The newly discovered exoplanet TOI-674b is a Neptune-like planet 23 times more massive than Earth. This exoplanet is unique because of its close orbit to its star, which should make it nearly impossible for it to contain water vapor.

TOI-674b completes an orbit around its red dwarf host star approximately every 2 days. This is an extremely short orbit and one we would not expect to see from this type of planet. Most Neptune-like planets orbit very far away from their star, much like Neptune itself. In fact, it is so rare to see these types of planets in such as close orbit that this orbital zone is often referred to as a “Neptune Desert.”

Because of TOI-674b’s extremely close orbit, researchers were surprised to find that it has water vapor in its atmosphere. Planets that orbit close to their star are normally too hot to contain water at all, so this puzzled the research team. Most water-containing planets orbit outside of what is known as the water ice line, where compounds such as water can condense into solid ice.

“Planets forming closer to their host stars inside the water ice line should have less atmospheric water than those forming further away… it [TOI-674b] almost certainly didn’t form this close to the star and needed to migrate into its current orbit somehow.” — University of Kansas doctoral student Jonathan Brande

More research on TOI-647b’s origins will be conducted in the future. The recently deployed James Webb Space Telescope will be studying the atmospheres of TOI-647b and other exoplanets to learn more about their composition and possible origin. Webb could reveal new information about this unique exoplanet, including how much water it contains and if heavier elements are also present.

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Rebecca Jean T.

Published author on NASA’s Radio Jove project. Researching science topics to deliver to you in bite-sized stories.