Rogue planet the size of Mars floating free in Milky Way
A Mars-sized planet discovered drifting through the Milky Way could be one of the galaxy’s rogue planets, astronomers have said.
Researchers believe the galaxy could be teeming with rogue planets moving through deep space on their own, after finding the smallest one to date.
Astronomers hope that studying these planets could help them unlock the turbulent past of planetary systems such as the Solar System.
The free-floating planet has a mass of somewhere between Earth and Mars, and is gravitationally unattached to any star. Its size has led experts to believe it could even be a rocky planet, compared to most rogue planets which are gas.
While most planets orbit a star, 10 similar planets about the size of Jupiter were discovered in 2011.
Radoslaw Poleski, of the Astronomical Observatory of the University of Warsaw, who was the study co-author, said: “When we first spotted this event, it was clear that it must have been caused by an extremely tiny object. We can rule out the planet having a star within about eight astronomical units.”
It is believed to be the smallest rogue world ever found.
Astronomers believe these free-floating planets formed in rotating discs of dense gas and dust around stars and were ejected from their parent planetary systems after gravitational interactions with other bodies.
Such planets are thought to be common but have proven to be extremely difficult to detect, with astronomers relying on a phenomenon known as gravitational microlensing to confirm their latest find.
This is only possible when an astronomer’s telescope lies in almost perfect alignment with the observed object and the source star. The result is an effect similar to a giant magnifying glass, where the light from a background star reveals the presence of a planet.
Researchers examined data collected from the microlensing surveys from the Galactic Bulge, part of the central Milky Way. They used the 1.3-metre Warsaw Telescope at Las Campanas Observatory in Chile to gather the data.
Przemek Mroz, a postdoctoral scholar at the California Institute of Technology and a lead author of the study published in Astrophysical Journal Letters, said: “The chances of observing microlensing are extremely slim because three objects – source, lens and observer – must be nearly perfectly aligned.”