Lead scientist Dr Jason Dittmann, from the Harvard-Smithsonian Centre for Astrophysics in Cambridge, US, said: "This is the most exciting exoplanet I've seen in the past decade".
The rocky planet, named LHS 1140b, orbits a red dwarf star 40 light years away.
In a paper detailing the discovery, the researchers also say they believe the planet has an atmosphere, adding that both star LHS 1140 and planet LHS 1140b are so close to Earth that "telescopes now under construction might be able to search for specific atmospheric gases in the future".
There's been compelling evidence lately that some of these planets around red dwarfs could, in fact, retain an atmosphere.That's the case of GJ 1132b, a hellish world with Venus-like temperatures around an M-dwarf star that, despite all odds, seems to hold on to an atmosphere. Meaning, one side of the planet always faces the star while the other faces away. That means in the next several years, new telescopes can spy its atmosphere in a targeted search for signs of life. It is over six-times as massive as Earth and about 1.5-times larger - fitting the description of a so-called "super Earth": It's bigger and more massive than Earth but smaller and less massive than the next biggest planet, Neptune.
The newfound planet is described in a paper appearing in the April 20thissue of the journal Nature.
The super-Earth and its parent star are located in the constellation Cetus, the Whale, 39 light years from the Sun, thus - relatively speaking - putting it in our galactic "neighbourhood", according to Felipe Murgas, the coauthor of the study and a researcher with Spain's Canary Islands Institute of Astrophysics.
Currently, the MEarth project is studying small stars that are less than a third the size of the Sun. "LHS 1140 is brighter at optical wavelengths because it's slightly bigger than the TRAPPIST-1 star".
The MEarth-South instruments enabled scientists to measure the planet's diameter and, using the HARPS spectrograph at the LaSilla ESO Observatory in Chile, they also were able to measure its mass, density and orbital period.
With Earth Day fast approaching, it's once again time for us to take stock of how we are treating our planet.
There are also lessons to glean from, and apply to, the TRAPPIST-1 system whose discovery was announced in February this year. This planet, designated LHS 1140 b, orbits its star every 25 days. They have called it LHS 1140b and said that it probably formed in its current location in a similar way to our planet.
Researchers believe it may be one of the best candidates for a closer look in the future by the James Webb Space Telescope, which NASA will launch in 2018. Three of the planets are in the Goldilocks zone, though all of the TRAPPIST-1 planets are believed to be rocky.
Just because LHS 1140b shares a few key traits with Earth doesn't mean this planet is exactly like ours, though.
"We originally thought it was just something amusing going on in the atmosphere", Harvard astronomer Jason Dittmann, the study's lead author, told Gizmodo.
In the case of LHS 1140b, the starlight is bright, the orbit is only 25 days and the planet is seen nearly edge-on from Earth. If the planet gets bombarded by too much high-energy radiation, at least we know to look elsewhere for alien life.
The planet is 10 times closer to the star than Earth is to the sun, but red dwarfs are much smaller and much cooler than the giant inferno that keeps us warm.
"For now, we do not have the technology to travel at a velocity close to the speed of light", Astudillo-Defru said. "Because LHS 1140 is nearby, telescopes now under construction might be able to search for specific atmospheric gases in the future". "We plan to search for water, and ultimately molecular oxygen".