Mysterious 'Sub-Neptunes' Are Probably Water Worlds

[Judi Lynn]

By Charles Q. Choi 2 days ago Science & Astronomy

Most exoplanets between Earth and Neptune in size are probably all wet.



An artist's illustration of the K2-138 system, which contains at least five "sub-Neptune" planets orbiting closely around their parent star.(Image: © R. Hurt (IPAC)/NASA/JPL-Caltech)


Water worlds that each possess thousands of times more water than Earth does may be more common than Earth-like rocky planets in the Milky Way galaxy, a new study finds.

Over the past 20 or so years, astronomers have confirmed the existence of thousands of exoplanets, or planets around other stars. NASA's recently deceased Kepler spacecraft discovered 2,702 confirmed exoplanets, and several thousand more "candidates" it found are awaiting confirmation.

Many exoplanets are quite unlike any planets in our solar system. For example, so-called super-Earths have diameters up to twice that of Earth, and "sub-Neptune" worlds are two to four times wider than Earth. (Neptune's diameter is about four times Earth's.)

Much remains hotly debated about sub-Neptunes, such as how they formed. Their compositions remain unknown, and understanding them could help shed light on these exoplanets' origins. Previous research suggested that sub-Neptunes were either gas dwarf planets with rocky cores surrounded by envelopes rich in hydrogen and helium, or water worlds with major amounts of liquid and frozen water in addition to rock and gas.

More:
https://www.space.com/water-world-exoplanets-common-milky-way.html?utm_source=notification