Scientists have discovered a new, frozen planet that has the same mass as that of Earth and is located 13,000 light-years away.
The finding may help understand the types of planetary systems that exist beyond our own.
The planet is likely far too cold to be habitable for life as we know it, however, because its star is so faint, researchers said.
"This 'iceball' planet is the lowest-mass planet ever found through microlensing," said Yossi Shvartzvald, a postdoctoral fellow at NASA's Jet Propulsion Laboratory in the US.
Microlensing is a technique that facilitates the discovery of distant objects by using background stars as flashlights.
When a star crosses precisely in front of a bright star in the background, the gravity of the foreground star focuses the light of the background star, making it appear brighter.
A planet orbiting the foreground object may cause an additional blip in the star's brightness.
In this case, the blip only lasted a few hours. This technique has found the most distant known exoplanets from Earth, and can detect low-mass planets that are substantially farther from their stars than Earth is from our sun.
The newly discovered planet, called OGLE-2016-BLG-1195Lb, aids scientists in their quest to figure out the distribution of planets in our galaxy.
An open question is whether there is a difference in the frequency of planets in the Milky Way's central bulge compared to its disk, the pancake-like region surrounding the bulge.
The planet is located in the disk, as are two planets previously detected through microlensing by NASA's Spitzer Space Telescope.
"Although we only have a handful of planetary systems with well-determined distances that are this far outside our solar system, the lack of Spitzer detections in the bulge suggests that planets may be less common toward the center of our galaxy than in the disk," said Geoff Bryden, astronomer at JPL.
Although the new planet is about the same mass as Earth, and the same distance from its host star as our planet is from our sun, the similarities may end there.
It is nearly 13,000 light-years away and orbits a star so small, scientists are not sure if it is a star at all. It could be a brown dwarf, a star-like object whose core is not hot enough to generate energy through nuclear fusion.
This particular star is only 7.8 per cent the mass of our Sun, right on the border between being a star and not.
Alternatively, it could be an ultra-cool dwarf star much like TRAPPIST-1, which was recently found to host seven Earth-size planets.
Those seven planets all huddle closely around TRAPPIST-1, even closer than Mercury orbits our sun, and they all have potential for liquid water.
However, OGLE-2016-BLG-1195Lb, at the sun-Earth distance from a very faint star, would be extremely cold - likely even colder than Pluto is in our own solar system, such that any surface water would be frozen.
The study was published in the Astrophysical Journal Letters.
Photograph: NASA
