K2-18b even has a neighbouring sister planet, the cleverly named K2-18c, but is unlikely to host life because it is slightly closer to its Sun.
Renewed interest in K2-18b after its initial discovery is the result of new research that determined the planet was both larger than Earth, and likely rocky, which is enough to classify it as a "Super Earth".
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.
Researchers at the University of Toronto in Canada made the discovery by scouring data collected by the European Southern Observatory (ESO).
K2-18b was first spotted by the astronomers in 2015. A recently discovered planet named Super Earth unveiling that it could hold numerous critical components of alien life. At that time they noticed that the super-Earth was orbiting the dwarf-star within its habitable zone.
"It was not a eureka moment because we still had to go through a checklist of things to do in order to verify the data", said Cloutier, lead author of the study published in the journal Astronomy and Astrophysics.
To measure the mass of K2-18b, Cloutier and his research partners used radial velocities of its host star measured by HARPS. By measuring the radial velocities of stars, which can be influenced by the presence of planets around those stars, HARPS can allow for the detection of the planets around the stars.
Harps can help determine the mass and radius of a planet to work out its density.
They found that the planet is probably mostly rocky with a gaseous atmosphere - like Earth, only bigger - however it may be a mostly water planet with a thick layer of ice, so further investigation is needed.
"Once all the boxes were checked it sunk in that, wow, this actually is a planet", he said.
Current technology prevents us from being able to definitively say which one it is but the fact that it could be either is a huge leap forward in our understanding of this distant solar system.
Engineers inspect the James Webb Space Telescope after cryogenic testing in Houston, November 19, 2017.
University of Montreal Professor René Doyon added: "There's a lot of demand to use this telescope, so you have to be meticulous in choosing which exoplanets to look at". In addition to a signal occurring every 39 days from the rotation of K2-18, and one taking place every 33 days from the orbit of K2-18b, he noticed a different signal occurring every nine days. "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".