Scientists from the Center for Astrobiology (CSIC-INTA) have discovered the largest collection of wandering planets to date. These worlds are free-floating as they were launched into interstellar space far from their stars. Using observations and archival data from various space and ground-based telescopes with more than 20 years of imaging, this rich population of planets discovered by astronomers would represent between 70 and 170 planets and would be found in a nearby region of the Milky Way known as the young stellar association Upper Scorpius about 420 light-years distant from Earth . This is by far the largest sample of such planets ever found in a single group, almost double the known number in the entire sky.
These planets lurk in the dark universe, without a star to illuminate them, so with our current instruments it is usually impossible to image them. The researchers took advantage of the fact that a few million years after their formation , these gas giant worlds are still hot enough to glow, making them detectable.
“We did not know how many worlds to expect and we are excited to have found so many, ” explained Núria Miret-Roig, from the University of Bordeaux (France) and leader of the study published in the journal Nature Astronomy.
If a good fraction of them are confirmed to be planets, it would suggest that the Milky Way is riddled with solar exiles like these. All rogue planets begin their existence in the same whirlpools of gas and dust that make up a typical solar system, but some of these clouds of matter may be too small to form the stellar part of the system and so are born without a star in sight (although others could have been ejected from their star system by gravitational interactions with other planets, of course).
The team used more than 80,000 observations. They measured the light from all members of the association in optical and near-infrared wavelengths. They also combined that data with measurements of their movement.
“We measured the small movements, colors and luminosity of tens of millions of sources in a large area of the sky. These measurements allowed us to reliably identify the faintest objects in this region,” Miret-Roig clarified.
According to Hervé Bouy, a co-author of the paper, “there could be several billion of these free-floating giant planets freely roaming the Milky Way without a host star.”
Finding so many of these rogue worlds can help astronomers find clues about how they form and how they come to be so alone in the universe.
Scientists hope to study them further when the VLT’s successor, the ESO Extremely Large Telescope (ELT), becomes operational in the next decade. Likewise, the Nancy Grace Roman Space Telescope, due to launch in 2027, will build the first census of them. It is likely to be ten times more sensitive to these objects than current ground-based telescopes, so much more information is to come in the years to come.
Referencia: N. Roig et al. “A rich population of free-floating planets in the Upper Scorpius young stellar association”. Nature Astronomy, 2021. DOI: 10.1038/s41550-021-01513-x