Their analysis revealed another surprise: K2-18b has a neighbor. At that time they noticed that the super-Earth was orbiting the dwarf-star within its habitable zone.
The planet is closer to its star than K2-18b, and probably too hot to be in the habitable zone.
Of course in addition to discovering K2-18b, the team also discovered that it has a sibling.
The two planets orbit a star called K2-18, which is a red dwarf star (dimmer and smaller than our sun) lying about 111 light-years from Earth. K2-18b, scientists say, could be in an excellent location for alien life to emerge-having flawless conditions for surface water, a fundamental ingredient for life, to exist.
In order to figure out whether the planet was a scaled-up version of Earth (mostly rock), or a scaled-down version of Neptune (mostly gas), Cloutier and co-authors had to first figure out the planet's mass.
The large rocky exoplanets were discovered using data collected by the European Southern Observatory's HARPS instrument.
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"So if we can detect that wobble, we can infer the presence of a planet, like this super-Earth, and we can actually measure its mass, which is great, because it tells you something about how big the planet is", Cloutier explained.
"Being able to measure the mass and density of K2-18b was tremendous, but to discover a new exoplanet was lucky and equally exciting", stated lead author Ryan Cloutier, an astronomy and astrophysics Ph.D student at the University of Toronto and the University of Montreal's Institute for Research on Exoplanets.
On top of that, the radial velocity measurements discovered by HARPS allowed researchers to calculate planets' mass, enabling them to measure their bulk density, and thus whether they are gaseous, rocky, whether they contain water, etc.
"With the current data, we can't distinguish between those two possibilities", Cloutier said.
The second planet popped up when Cloutier noticed a different signal in the data than from K2-18b, which orbits its star every 33 days. As per the researchers, the James Webb Space Telescope (JWST) will play a significant role in finding out further information about this super-Earth.
Researcher Professor René Doyon said that there's a lot of demand to use this telescope, so you have to be accurate in picking which exoplanets to look at.
Engineers inspect the James Webb Space Telescope after cryogenic testing in Houston, November 19, 2017. "But whether or not there is surface water, we're going to have to do some follow up observations to figure that out for sure, because right now we just don't know".