Planets are known to be orbiting a star, just as Earth goes around the Sun, however, scientists have discovered 70-172 such planets that do not have a parent star. This is by far the largest sample of free-floating planets discovered at once and is almost double the number of free-floating planets known to date.
Free-flowing planets are the result of a star formation process, however, the origin of the newly discovered planets remains a mystery. These planets are celestial objects with masses of less than 13 times the mass of Jupiter which are not bound to a star but just roam among them.
Researchers are pondering over questions like do they form like stars through the gravitational collapse of small clouds of gas? Or do they form like planets around stars and are then dynamically ejected or stripped off?
In a paper published in the journal Nature Astronomy, astronomers said that ejection from planetary systems might have a contribution to the formation of these free-floating planets. The researchers looked for these objects in the Upper Scorpius young stellar association, the closest star-forming regions to the Sun.
This image shows the locations of 115 potential free-floating planets in Upper Scorpius. (Photo: astronomycommunity.nature.com)
Astronomers collected all the pictures available in this region, compiling over 80,000 wide-field images, and built the largest catalogue of observations in the region.
“Identifying free-floating planets is a major challenge, in many ways, similar to the “needle in the haystack” parable. One must identify the rare planetary-mass members (the “needles”, typically a few hundred) within the overwhelming multitude of field stars and background galaxies (the “haystack”, millions of interlopers),” said Núria Miret Roig, postdoctoral researcher and lead author of the paper in a blog.
Astronomers said that the free-floating planets discovered in this study are excellent targets for follow-up studies, for instance with the James Webb space telescope. The newly discovered worlds will be interesting to study since their atmosphere has developed in the absence of a star and the comparison with atmospheres of planets orbiting stars will provide key details about their formation and properties.
“Extrapolating the fraction of free-floating planets that we measured in Upper Scorpius to the entire Milky Way, there should be several billions of Jupiters roaming the Milky Way without a host star,” Núria Miret Roig said, adding that the number would be even greater for Earth-mass planets since they are known to be more common than massive planets.