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| Lead image: An artist’s interpretation of a rogue planet with the Rho Ophiuchi cloud complex in the background. Credit: Bordeaux University / ESO. |
A team of astronomers have discovered at least 70 new rogue planets. There may even be up to 170 rogue, or free-floating planets (FFPs). It’s the largest group of rogue planets discovered at once.
The new study outlining the research has been published in Nature Astronomy. The first author, Núria Miret-Roig, is an astronomer at the Laboratoire d’Astrophysique de Bordeaux, France and the University of Vienna, Austria. Miret-Roig said, ‘We did not know how many to expect and are excited to have found so many.’
To find so many rogue planets, the team worked through about 20 years of data from various telescopes, including European Southern Observatory (ESO) facilities. ‘We measured the tiny motions, the colors and luminosities of tens of millions of sources in a large area of the sky,’ said Miret-Roig. ‘These measurements allowed us to securely identify the faintest objects in this region, the rogue planets.’ Rogue planets are elusive. Their masses are similar to planets in our Solar System, but without a star to orbit, rogue planets are exceedingly hard to spot.
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| The very small red dot at the center of this image (click to enlarge) is a recently discovered rogue planet, located in the area of the sky occupied by Upper Scorpius and Ophiucus. Credit: Bordeaux University / ESO |
Per the ESO news release, the team used observational data from the ESO’s Very Large Telescope (VLT), the Visible and Infrared Survey Telescope for Astronomy (VISTA), the VLT Survey Telescope (VST) and the MPG/ESO 2.2-meter telescope in Chile. ‘The vast majority of our data come from ESO observatories, which were absolutely critical for this study. Their wide field of view and unique sensitivity were keys to our success,’ said Hervé Bouy, an astronomer at the Laboratoire d’Astrophysique de Bordeaux, France, and project leader of the new research. ‘We used tens of thousands of wide-field images from ESO facilities, corresponding to hundreds of hours of observations, and literally tens of terabytes of data.’ The team also used data from the European Space Agency’s Gaia Satellite, which is a space-based telescope. Combining data from ground- and space-based telescope for the new research is a momentous occasion.
What makes a rogue planet so difficult to find? A rogue planet is far away from stars, so rogue planets are very dark and challenging to image. However, for a few million years after they form, rogue planets still glow, so they can be detected by sensitive cameras on large telescopes. The ones found by Miret-Roig and her team have masses comparable to Jupiter and the planets the team found are within the Scorpius and Ophiuchus constellations.
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| This image shows the location of 115 possible rogue planets, as noted by red circles. The precise number of rogue planets discovered by the team range from 70 and 170, depending upon the age assumed for the region that was studied. This image assumes an intermediate age. Credit: Bordeaux University / ESO |
A previous study by US scientists claims that the Milky Way may be home to more than 100 billion free-floating planets. ‘There could be several billions of these free-floating giant planets roaming freely in the Milky Way without a host star,’ Bouy added. By studying the newly located rogue planets, astronomers hope to learn more about planet formation. Currently, there are two primary theories about rogue planet formation. Some people believe that the planets form from a gas cloud collapsing that was too small to form a star. Others think that rogue planets may be planets that somehow got away from a parent system. The team’s paper outlines that they found an excess of rogue planets by up to a factor of seven, which suggests that other formation mechanisms may be at play, and also adds credibility to the planetary system ejection theory.
Advancing technology will aid in rogue planet discovery and research, including the ESO’s new Extremely Large Telescope (ELT), which is currently under construction in the Chilean Atacama Desert. The ELT should begin observations later this decade. ‘These objects are extremely faint and little can be done to study them with current facilities,’ said Bouy. ‘The ELT will be absolutely crucial to gathering more information about most of the rogue planets we have found.’