Super Earth K2-18b: Exoplanet That Could Harbor Extraterrestrial Life Has a Neighbor Hiding Behind It

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An artist illustrates the K2-18 planetary system, which contains super Earths. Alex Boersma

Astronomers have identified a distant exoplanet as a "super-Earth" that has the potential to harbor alien life. On top of this, the team also discovered that this planet, called K2-18b, has another, similar world hiding behind it.

A super-Earth is a planet with a mass higher than Earth but smaller than larger bodies like Uranus and Neptune.

The two new super-Earths orbit a red-dwarf star around 111 light years away. K2-18b, scientists say, could be in an excellent location for alien life to emerge—having perfect conditions for surface water, a fundamental ingredient for life, to exist.

Hunting planets

Scientists combed the skies with the European Southern Observatory's planet-hunting HARPS device in Chile. They found the planets circling the red dwarf star K2-18, which is part of the constellation, Leo.

The discovery of the first planet, K2-18b, took place in 2015. Sitting within the habitable zone of the star, astronomers have been investigating whether or not it could support life. This meant finding out if K2-18b was a hunk of rock, like Earth, or a dense body of gas, like Jupiter.

Using the fiber-optic HARPS technology, the astronomers watched the changing position and speed of stars. This kind of movement can indicate that a star is being pulled by the gravitational force of orbiting planets. By collecting so-called "radial velocity" data on K2-18, the scientists were able to estimate the size of K2-18b.

"If you can get the mass and radius, you can measure the bulk density of the planet and that can tell you what the bulk of the planet is made of," lead author Ryan Cloutier said in a statement.

Using sophisticated machine-learning techniques, the team figured out the planet could well be an Earth-like planet made mostly of rock and with a gaseous atmosphere. Alternatively, the planet could be made up of water encased in a thick crust of ice. Thier findings have been submitted to the journal Astronomy & Astrophysics.

Second super-earth discovery

As well as taking one giant leap closer to finding a potentially habitable exoplanet, the team also uncovered a second Earth-like planet orbiting K2-18. This super-Earth—K2-18c—unfortunately, is a much poorer candidate for life. It sits too close to its star, meaning the surface is probably too hot to support life.

The identification of two new super-Earths, however, is still a significant advance for astrophysics. According to study authors, the discovery sheds important light on the prevalence of multi-planet systems around dwarf stars like K2-18.

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

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Engineers inspect the James Webb Space Telescope after cryogenic testing in Houston on November 19. Chris Gunn/NASA/Flickr

Researchers will have to wait until 2019 to confirm the atmospheric conditions of K2-18b, when NASA's James Webb Space Telescope is set to launch. "There's a lot of demand to use this telescope, so you have to be meticulous in choosing which exoplanets to look at," said study co-author René Doyon. "K2-18b is now one of the best targets for atmospheric study, it's going to the near top of the list."