Two super-Earths found around star K2-18

Astronomers have detected a pair of super-Earths just 111 light years away.
By Joseph Scalise | Dec 08, 2017
A group of international astronomers looking at data from the European Southern Observatory (ESO) have found that an exoplanet known as K2-18b could be a scaled-up version of Earth, and that is may also have an Earth-like neighbor.

Both planets move around K2-18, a red-dwarf star located roughly 111 light years away in the constellation Leo. Researchers first found K2-18b in 2015. At the time, they noted that it is in its star's habitable zone -- meaning it could potentially host both liquid surface water and life -- which made it an interesting topic of study.

To get a closer look, astronomers in the new studyused the High Accuracy Radial Velocity Planet Searcher (HARPS) and the ESO's 3.6m telescope at La Silla Observatory, in Chile to better look at K2-18. HARPS is key for such a process because it allows scientists to accurately measure the radial velocities of stars, which are affected by the presence of planets, and make note of any small planets around them.

To determine if K2-18b was a scaled-up version of Earth -- meaning it is mostly rock -- or a scaled-down version of Neptune -- meaning it is mostly gas -- the team first needed to figure out the exoplanet's mass. They did that through a machine-learning approach, which revealed K2-18b is either a mostlymostly rocky planet with a small gaseous atmosphere or a mostly-water planet with a thick layer of ice on top of it.

"With the current data, we can't distinguish between those two possibilities," saidlead author Ryan Cloutier, a PhD student in U of T Scarborough's Centre for Planet Science, according to Phys.org. "But with the James Webb Space Telescope we can probe the atmosphere and see whether it has an extensive atmosphere or it's a planet covered in water."

In addition to their discovery of K2-18b, the team also noticed another rotation taking place around K2-18 once every nine days. After ruling out that the signal was not ambient noise, they found another planet moving around the star. The body -- known as K2-18c -- is closer to K2-18 than K2-18b, and is likely too hot to be in the habitable zone. Even so, it appears to be another super-Earth meaning it has a mass similar to Earth.

"Being able to measure the mass and density of K2-18b was tremendous, but to discover a new exoplanet was lucky and equally exciting," added Cloutier, according toNewsweek.

This new information makes K2-18b one of the best targets for atmospheric study. It will be looked at in greater detail by the James Webb Space Telescope, which is set to launch in 2019.

The new findings are in the outlined in the journalAstronomy and Astrophysics.

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