Amazing stuff!
"Planets ... But some can go rogue, breaking away from their orbit and meandering through the galaxy. Researchers have discovered one such free floater, named Gaia24cdn, which they reported last week in Science.
Spotting rogue planets is challenging because they emit hardly any light. While astronomers typically track exoplanets by the dips in light they cause when passing in front of a star, astronomers must find rogue planets through subtle gravitational effects. Unfortunately, the gravitational method cannot reveal the distance or mass of a planet, making our knowledge of these floaters limited.
Using Polish and Korean-run ground-based telescope networks and the European Space Agency’s Gaia space telescope, a team detected a fleeting gravitational event where an object magnified the light from a star behind it.
Due to the multiple telescope angles, the team was able to determine the object’s location and mass: about 10,000 light-years from Earth and comparable to the mass of Saturn. Since the telescopes did not detect a host star, the researchers determined the object was a rogue planet. They think it likely formed in a typical solar system, then got expelled during a period of gravitational turmoil caused by interactions with neighboring planets or unstable stars.
Rogue planets like Gaia24cdn won’t be so sneaky for long. ... that the impending launch of the Nancy Grace Roman Space Telescope will “allow [for] the detection of thousands of new planets and the rigorous testing of planet formation models.”"
From the abstract (Perspective):
"Planets are often found orbiting a star or a group of multiple stars. However, planets have also been observed to drift independently without a known accompanying star system. These celestial objects, called free-floating or rogue planets, are difficult to detect because they don’t emit enough light to be spotted through current generation telescopes. ... report the discovery of a rogue planet by a short-lived microlensing event, an astronomical phenomenon in which the gravitational effect of a foreground object magnifies the light from a background star.
By combining simultaneous measurements on Earth and in space, the mass of the planet was estimated to be 22% that of Jupiter. This finding demonstrates how coordinated observations can overcome difficulties in determining both the position and mass of a rogue planet and improve the understanding of how these planets form. ..."
From the editor's summary and abstract:
"Editor’s summary
Gravitational microlensing causes the apparent brightness of a background star to vary when a foreground object passes across our line of sight. The mass and distance of the lensing object are usually degenerate parameters. Dong et al. have identified a microlensing event caused by a planetary-mass object with no associated host star ... By combining observations from Earth and a distant spacecraft, the mass-distance degeneracy can be broken, allowing for measurement of the lensing object’s mass, which is similar to Saturn’s. The researchers argue that this free-floating object did not form in isolation but was ejected from a host planetary system by dynamical interactions. ...
Abstract
A 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.
We report a microlensing event—KMT-2024-BLG-0792/OGLE-2024-BLG-0516, which was observed from both ground- and space-based telescopes—that breaks the mass-distance degeneracy. The event was caused by an object with
Jupiter masses that is either gravitationally unbound or on a very wide orbit. Through 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). Dynamical processes then ejected it from its birthplace, producing a free-floating object."
Two views of a rogue planet (Perspective, no public access)
A free-floating-planet microlensing event caused by a Saturn-mass object (no public access)
A free-floating-planet microlensing event caused by a Saturn-mass object (preprint, open access)
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