The planet, called KOI-314c, weighs the same as earth but it is 60 percent larger in diameter, meaning that it must have a very thick, gaseous atmosphere, said a study.
"This planet might have the same mass as earth but it is certainly not earth-like," said David Kipping of the Harvard-Smithsonian Centre for Astrophysics (CfA).
It proves that there is no clear dividing line between rocky worlds like earth and fluffier planets like water worlds or gas giants, he added in the study published in the Astrophysical Journal.
KOI-314c is the lightest planet to have both its mass and physical size measured.
The previous record holder for a planet with a measured mass (Kepler-78b) weighed 70 percent more than earth, the study added.
The research team gleaned the planet's characteristics using data from the National Aeronautics and Space Administration's (NASA) Kepler spacecraft.
The new planet orbits a dim, red dwarf star located approximately 200 light-years away.
It circles its star every 23 days. The team estimated its temperature to be 220 degrees Fahrenheit - too hot for life as we know it, said the study, funded by NASA and the National Science Foundation.
"At first, we were disappointed it wasn't a moon but then we soon realised it was an extraordinary measurement," concluded Kipping.
--IANS (Posted on 07-01-2014)