Astronomers took a second look at an exoplanet and discovered that it is probably a super-Earth. They also discovered that the planet probably has a neighbor.
The two planets orbit around a star called K2-18, which is a red dwarf star (dimmer and smaller than our sun) located about 111 light-years from Earth. The star is part of the Leo constellation. In 2015, another research team discovered the planet K2-18b and observed that it is in the habitable zone. Since K2-18b is probably rocky, this means that the planet could have liquid water on its surface, which is one of the many conditions to sustain life.
"Being able to measure the mass and density of K2-1
The newly found super-terrestrial state of K2-18b comes after a series of other recent rocky discoveries related to the planet. Last month, another research team announced that the Ross Earth mass 128b, which orbits a red dwarf star 11 light-years from Earth, is perhaps the most likely candidate to host alien life. It is the closest rocky planet found in a habitable zone found from Proxima Centauri b in 2016, which is only four light-years away. And in February, another scientific team announced that the planet TRAPPIST-1 hosts seven rocky planets, including some that could be in the habitable zone.
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The K2-18b researchers used data from the high-speed planetary finder of search for high precision planets (HARPS) at the La Silla Observatory in Chile. HARPS is designed to measure the radial velocities of stars, which are influenced by the presence of planets in orbit.
Previously, researchers were not sure if K2-18b was a super-Earth, which means it is a bit larger than our planet, but mainly rocky, or a mini-Neptune composed mainly of gas. The HARPS measurements provided information about the mass of the planet, while the radius of the planet was determined by other instruments that measure how much light it blocks from its parent star.
"If you can get the mass and the radius, you can measure the apparent density of the planet and that can tell you what the bulk of the planet is made of," Cloutier said. The data from the researchers showed that K2-18b is a rocky planet with a small gas atmosphere (similar to Earth) or a water planet that has a lot of ice on its surface.
Finding out what's really true will require more observations, perhaps from NASA's powerful James Webb space telescope, to be launched in 2019. But the research team acknowledged that many other teams will request the use of the new telescope, so they will need to justify your goal carefully.
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The second planet appeared when Cloutier noticed a different signal in the data than that of K2-18b, which orbits its star every 33 days. The second signal happened every nine days. After ruling out the possibility of noise, astronomers announced a second planet called K2-18c. The planet is also a super-Earth, but probably orbits too close to its parent star to have liquid water on its surface.
Other team researchers are affiliated with the Geneva Observatory in Switzerland, the French University of Grenoble and the University of Oporto in Portugal. The research will be published in the journal Astronomy and Astrophysics and is currently available on the Arxiv website.
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