It is one of the starkest concepts in astronomy, a free-floating planet, not connected to any parent star but drifting by itself in the dark void of space.
Canadian and French researchers have announced the discovery of the best candidate yet for that category of celestial bodies, an independent planet roving just 100 light years from Earth.
In a paper appearing Wednesday in the journal Astronomy & Astrophysics, French astronomers working with colleagues at the Université de Montréal said that their discovery opens exciting new perspectives in our scientific knowledge about planets beyond the solar system.
"Intrinsically, they're interesting on a human level, as solitary planets in space," said Université de Montréal researcher Loïc Albert. "But they can also be a proxy for the study of other planets. They can be models to help us study other objects that are harder to see."
Until now, scientists researching planets outside the solar system made most of their discoveries through indirect observations, deducting the existence of those exo-planets through their impact on a star's brightness or movement.
The newly discovered planet is, however, close and visible to telescopes, thus making it amenable to further detailed studies.
The free-floating planet is part of a group of moving stars called AB Doradus Moving Group. Without the brightness of its own sun, it can only be seen in the infrared spectrum and was detected by data from the Canada-France-Hawaii Telescope and the Chile-based European Southern Observatory's Very Large Telescope.
The planet has been named CFBDSIR2149 (since it was discovered during a project called CFBDSIR, the abbreviation for Canada-France Brown Dwarfs Survey Infra Red.)
CFBDSIR2149 is 10 times wider than Earth and 1,000 times heavier.
The planet is likely of a magenta or dark pink colour, with no solid surface, an inhospitable world with a surface temperature of about 400 Celsius.
"For a planet, it is very hot, but it's very cold for a star," Dr. Albert said.
The concept of free-floating planets is connected with the existence of brown dwarfs.
Brown dwarfs are between 13 to 75 times the mass of Jupiter, the largest planet in the solar system, which itself is 300 times more massive than Earth.
While still very large compared to planets, brown dwarfs are not massive enough to trigger the nuclear hydrogen fusion reaction that would turn them into a full-fledged star.
Free-floating planets display similar characteristics but are too small to even be brown dwarfs.
The paper says that free-floating planets are either space bodies that were ejected at the birth of their solar system, or they are failed brown dwarfs.
Either scenario suggest that there would be numerous independent planets.
"This would mean free-floating, frozen-down versions of Jupiters, Neptunes and perhaps Earths are common throughout the Milky Way," the paper concludes.