‘Free-floating’ planet unattached to any star discovered in the Milky Way

An artist’s impression of a gravitational microlensing event by a free-floating planet. (Credits: University of Warsaw / SWNS)

Astronomers have discovered a ‘free-floating’ planet in the Milky Way that is slightly smaller than Earth and is gravitationally unattached to any star.

Scientists say it is the smallest ‘rogue’ planet found to date.

In 2011, the team found 10 such celestial objects that were about the size of Jupiter and did not have parent stars within 10 astronomical units. One AU is equivalent to the distance between the Earth and the Sun.

While most known planets orbit a star, the researchers believe the galaxy may be teeming with rogue planets, possibly outnumbering the number of stars in the Milky Way.

The scientists took advantage of an astronomical phenomenon known as ‘gravitational microlensing’ to spot the planet, which revealed itself by bending the light of more distant stars.

The result was an effect that is much like a giant magnifying glass, which brightens light from a background ‘source’ star to reveal the presence of the massive object.

Gravitational microlensing is only possible when an astronomer’s telescope lies in almost perfect alignment with the observed object and the source star.

Przemek Mroz, a postdoctoral scholar at the California Institute of Technology and a lead author of the study published in Astrophysical Journal Letters, said: ‘Chances of observing microlensing are extremely slim because three objects – source, lens and observer – must be nearly perfectly aligned.’

The researchers examined data collected from microlensing surveys of the Galactic Bulge, which is the central part of the Milky Way.

Researchers examined data from surveys of the Galactic Bulge at the center of the Milky Way (Credits: Getty Images/Science Photo Library)

They used the 1.3-metre Warsaw Telescope at Las Campanas Observatory in Chile to gather the data.

The researchers said the newly detected planet is the smallest rogue world ever found, with models indicating it may have a mass somewhere between Earth and Mars.

Radoslaw Poleski, from the Astronomical Observatory of the University of Warsaw, who was 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.’

Astronomers believe free-floating planets may have formed in the rotating discs of dense gas and dust around stars and were ejected from their parent planetary systems after gravitational interactions with other bodies.

They say studying these objects could enable astronomers to learn more about the turbulent past of planetary systems such as the Solar System.

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