Using observations and archival data from several space- and ground-based telescopes, astronomers have discovered a rich population of free-floating planets — between 70 and 170 such objects — in a nearby region of the Milky Way known as the Upper Scorpius young stellar association. This is the largest sample of such planets found in a single group and it nearly doubles the number known over the entire sky.
This artist’s impression shows an example of a free-floating planet with the Rho Ophiuchi cloud complex visible in the background. Image credit: ESO / M. Kornmesser.
To date, most exoplanets have been detected through modulations induced in their host stars. As such, the vast majority of known exoplanets are gravitationally bound to stars.
However, several free-floating planets have been discovered over the last two decades in surveys of nearby star-forming regions, young associations, the solar neighborhood and in gravitational micro-lensing surveys of the Galactic field.
These ultra-faint objects are less than about 13 Jupiter masses and are not bound to a star or brown dwarf but rather wander among them.
They are incapable of sustaining nuclear fusion and steadily fade in time, making them easier to observe when they are very young.
“We did not know how many to expect and are excited to have found so many,” said Dr. Núria Miret-Roig, an astronomer at the Laboratoire d’Astrophysique de Bordeaux and the University of Vienna.
In the study, Dr. Miret-Roig and colleagues used observations and archival data from a number of large observatories, including facilities from NSF’s NOIRLab, ESO telescopes, the Canada-France-Hawaii Telescope, and the Subaru Telescope, amounting to 80,000 wide-field images over 20 years of observations.
They found between 70 and 170 free-floating planets (depending on the assumed age) in the Upper Scorpius young stellar association, a star-forming region located approximately 420 light-years away within the Scorpius and Ophiuchus constellations.
“We measured the tiny motions, the colors and luminosities of tens of millions of sources in a large area of the sky,” Dr. Miret-Roig said.
“These measurements allowed us to securely identify the faintest objects in this region, the rogue planets.”
“There could be several billions of these free-floating giant planets roaming freely in the Milky Way without a host star,” said Dr. Hervé Bouy, an astronomer at the Laboratoire d’Astrophysique de Bordeaux.
The results were published in the journal Nature Astronomy.
_____
N. Miret-Roig et al. A rich population of free-floating planets in the Upper Scorpius young stellar association. Nat Astron, published online December 22, 2021; doi: 10.1038/s41550-021-01513-x
