This image has been used for illustrative purpose.

Niloufar Saleem, Staff Reporter

Exoplanets which are a common sight in the Milky Way, are usually noticed to be orbiting a star, but in an unusual finding, scientists have discovered an Earth-sized free-floating rogue planet which does not orbit any star.

Many astronomers have previously found evidence of such planets actually existing, but this is the first time it has been spotted.

"Our discovery demonstrates that low-mass free-floating planets can be detected and characterised using ground-based telescopes," said study co-author Andrzej Udalski, Professor at University of Warsaw in Poland.

Free-floating planets emit virtually no radiation and -- by definition -- they do not orbit any host star, so they cannot be discovered using traditional methods of astrophysical detection.

These rogue planets can be further examined by what is called the microlensing.

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Microlensing results from Einstein's theory of general relativity -- a massive object (the lens) may bend the light of a bright background object (the source).

The lens' gravity acts as a huge magnifying glass which bends and magnifies the light of distant stars.

Modern surveys hunting for gravitational microlensing events are monitoring hundreds of millions of stars in the Milky Way centre, where the chances of microlensing are highest.

"When we first spotted this event, it was clear that it must have been caused by an extremely tiny object," said co-author of the study Radoslaw Poleski from the Astronomical Observatory of the University of Warsaw.