Free floating planets, or wandering planets, roam the Milky Way without orbiting a star. Now, through simultaneous observations from ground and space, a team of scientists has detected one of these planets and has measured its mass and distance.
The study, carried out by an international team of astronomers and led by Subo Dong of Peking University (China), demonstrates that coordinated observations can overcome the difficulties in determining both the position and mass of a wandering planet and improve the understanding of how these planets form.
Details of the discovery were published in the journal Science.
Most planets are gravitationally linked to one or more stars but, as anticipated by theories of planetary formation and evolution, there are planets that wander around the galaxy without orbiting any star: they are called wandering planets.
These planets are very difficult to observe because they do not emit enough light to be seen with current telescopes but, despite the difficulties, in recent years a few have been identified, some more massive than Jupiter.
The most common methods for discovering planets use the variation in light that is produced in a star when one of the bodies that orbit it passes in front of it periodically (transit method), or measure the gravitational variations produced by its movements around the star (Doppler method).
However, since they do not orbit any star, these methods are not useful for detecting rogue planets. To do this, astronomers use a phenomenon called gravitational microlensing.
This is a consequence of the general theory of relativity, which predicts that a massive object bends the path of light arriving from another body behind it. This phenomenon, therefore, acts as a magnifying crystal that allows the observation of distant objects and detects a lens (in this case a planet) in the foreground.
In the study, Dong and his colleagues report the discovery of a new free planet that was discovered thanks to a fleeting microlensing phenomenon.
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Rogue planets could form around stars
Unlike previous detections, the team observed the event, for the first time, simultaneously from Earth and space, with observations from ground-based telescopes (from the Polish OGLE project – Optical Gravitational Lens Experiment – and the Korean Microlensing Telescope Network), and observations from the European Gaia space telescope, located 1.5 million kilometers from Earth.
Combining data from the telescopes, the team determined that the planet’s mass is similar to that of Saturn and equivalent to 22% of the mass of Jupiter, and that it is 3 parsecs away (an astronomical unit for measuring great distances) from Earth.
Because the mass of this planet is comparable to that of Saturn, the team argues that it probably formed within a planetary system analogous to other planets, and not in isolation like a small star or a brown dwarf, which are considered neither stars nor planets because they are objects more massive than planets but not as massive as stars.
Therefore, the study suggests, smaller rogue planets could form around stars, within a planetary system, before being ejected from their orbit through dynamic interactions with other sister or neighboring planets, or with a star within a binary system.
In a Perspective published in the same journal, Galvin Coleman, from Queen Mary University of London, recalls that the first rogue planet was discovered in 2000, when an astronomical object with a mass similar to that of Jupiter was directly observed in a nearby star-forming region, the Orion Nebula.
Since then, he notes, although studies to date have only revealed a handful of rogue planets, detections are expected to increase in the coming years thanks to observations from NASA’s Nancy Grace Roman Space Telescope, which is scheduled to launch in 2027.
“This observatory will survey enormous expanses of the sky 1,000 times faster than the Hubble Telescope and in infrared light, and this will allow the detection of thousands of new planets and the rigorous testing of planetary formation models,” he points out.
Meanwhile, the astrophysicist emphasizes, the discovery by Dong and his team demonstrates “the effectiveness of the microlensing technique and how the detection of wandering planets can shed light on the process of planetary formation.”
With information from EFE
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