Mysterious Galactic Nomads: At Least 70 Rogue Planets Uncovered in Our Milky Way
Rogue planets are elusive cosmic objects that have masses comparable to those of the planets in our Solar System but do not orbit a star, instead roaming freely on their own. Not many were known until now, but a team of astronomers, using data from several European Southern Observatory (
Astronomers have used ESO telescopes to detect at least 70 rogue planets in our
To spot so many rogue planets, the team used data spanning about 20 years from a number of telescopes on the ground and in space. “We measured the tiny motions, the colors and luminosities of tens of millions of sources in a large area of the sky,” explains Miret-Roig. “These measurements allowed us to securely identify the faintest objects in this region, the rogue planets.”
The team used observations from ESO’s
This artist’s animation shows what a rogue planet — a planet that does not orbit a star but instead roams freely on its own — could look like. Recently, a team of astronomers, using data from several European Southern Observatory (ESO) telescopes and other facilities, discovered at least 70 new rogue planets in a region of the sky occupied by Upper Scorpius and Ophiucus. The cloud complex Rho Ophiuchi is visible in the background.
The team also used data from the European Space Agency’s Gaia satellite, marking a huge success for the collaboration of ground- and space-based telescopes in the exploration and understanding of our Universe.
The study suggests there could be many more of these elusive, starless planets that we have yet to discover. “There could be several billions of these free-floating giant planets roaming freely in the Milky Way without a host star,” Bouy explains.
This animation lets us plunge into a region of the sky occupied by Upper Scorpius and Ophiucus, where the largest group of rogue planets — at least 70, highlighted in the circles — has recently been discovered. Here we zoom in on one of them.
By studying the newly found rogue planets, astronomers may find clues to how these mysterious objects form. Some scientists believe rogue planets can form from the collapse of a gas cloud that is too small to lead to the formation of a star, or that they could have been kicked out from their parent system. But which mechanism is more likely remains unknown.
Further advances in technology will be key to unlocking the mystery of these nomadic planets. The team hopes to continue to study them in greater detail with ESO’s forthcoming Extremely Large Telescope (ELT), currently under construction in the Chilean Atacama Desert and due to start observations later this decade. “These objects are extremely faint and little can be done to study them with current facilities,” says Bouy. “The ELT will be absolutely crucial to gathering more information about most of the rogue planets we have found.”
- The exact number of rogue planets found by the team is hard to pin down because the observations don’t allow the researchers to measure the masses of the probed objects. Objects with masses higher than about 13 times the mass of Jupiter are most likely not planets, so they cannot be included in the count. However, since the team didn’t have values for the mass, they had to rely on studying the planets’ brightness to provide an upper limit to the number of rogue planets observed. The brightness is, in turn, related to the age of the planets themselves, as the older the planet, the longer it has been cooling down and reducing in brightness. If the studied region is old, then the brightest objects in the sample are likely above 13 Jupiter masses, and below if the region is on the younger side. Given the uncertainty in the age of the study region, this method gives a rogue planet count of between 70 and 170.
“A rich population of free-floating planets in the Upper Scorpius young stellar…