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<\/p>\nA population of free-floating planets is known from gravitational microlensing surveys. None have a directly measured mass, owing to a degeneracy with the distance, but the population statistics indicate that many are less massive than Jupiter. Now, astronomers have discovered a microlensing event that breaks the mass-distance degeneracy. Designated KMT-2024-BLG-0792\/OGLE-2024-BLG-0516, the event was caused by an exoplanet about 21.9% the mass of Jupiter at a distance of 9,785 light-years (3,000 parsecs) from the center of our Milky Way Galaxy.<\/p>\n
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An artist\u2019s impression of a free-floating exoplanet. Image credit: Sci.News.<\/p>\n
Planets are most often found bound to one or more stars, yet a growing body of evidence shows that some wander the galaxy alone.<\/p>\n
These objects, called free-floating or rogue planets, lack any known stellar companion.<\/p>\n
And, since they don\u2019t emit very much light, they reveal themselves only through their subtle gravitational effects \u2014 a phenomenon called microlensing.<\/p>\n
One of the main limitations of this discovery method is that it cannot determine the distance to these planets, making independent measurement of their mass difficult.<\/p>\n
As a result, much about this elusive population of solitary worlds remains speculative.<\/p>\n
In new research, Dr. Subo Dong, an astronomer at Peking University and the National Astronomical Observatories, and colleagues detected a new free-floating planet via a fleeting microlensing event: KMT-2024-BLG-0792\/OGLE-2024-BLG-0516.<\/p>\n
However, unlike previous detections, they uniquely observed this microlensing event simultaneously from both Earth and space, using several ground-based surveys alongside ESA\u2019s Gaia space telescope.<\/p>\n
Tiny differences in the timing of the light reaching these distantly separated vantage points enabled measurement of the microlensing parallax, which, when combined with finite-source point-lens modeling, allowed the authors to determine the planet\u2019s mass and location.<\/p>\n
\u201cThrough comparison with the statistical properties of other observed microlensing events and predictions from simulations, we infer that this object likely formed in a protoplanetary disk (like a planet), not in isolation (like a brown dwarf),\u201d the astronomers said.<\/p>\n
\u201cDynamical processes then ejected it from its birthplace, producing a free-floating object.\u201d<\/p>\n