It appears that rogue planets – free floating worlds that aren’t gravitationally bound to a parent star – might be more common than we thought. New data from the James Webb Space Telescope have revealed 540 (yes, that’s right) planetary-mass objects in the Orion Nebula and Trapezium Cluster.
If confirmed, this would be by far the largest sample of rogue planets ever discovered.
Last year, astronomers found 70 free floating worlds throughout the Milky Way.
Astronomers Samuel Pearson and Mark McCaughrean of the European Space Agency made the observations and posted a preprint paper to arXiv. The paper has yet to be peer reviewed, but has been submitted to Nature.
The researchers say a near-infrared survey from JWST allowed them to discover and characterize this large sample of 540 planetary-mass candidates. The team says these planetary mass objects (PMOs) are too small to be stars, as their masses are well below the traditional cutoff for a deuterium-burning brown dwarf, even down to 0.6 Jupiter mass — not much more massive than Saturn.
Within the large group of rogue planets are 42 pairs of planets that are gravitationally bound together, something that’s never been observed before. The astronomers named them Jupiter Mass Binary Objects, or JuMBOs.
Graphic of a rogue star being kicked out of a galaxy. Credit: NASA, ESA, and G. Bacon (STScI)
“How pairs of young planets can be ejected simultaneously and remain bound, albeit weakly at relatively wide separations, remains quite unclear,” the researchers wrote in their paper.
“The Jupiter Mass Binary Objects or JuMBOs are a really big discovery, we believe,” said McCaughrean, a senior adviser for science and exploration at ESA, on Mastodon. In the pre-print, researchers said that these planetary-mass binary objects is “a result that is highly unexpected and which challenges current theories of both star and planet formation.”
The conventional definition of a planet is that it is in orbit around a star. Additionally, current theories of planetary formation suggest that Jupiter-sized objects can only be formed through the process that gives rise to stars inside the clouds of dust and gas found in a nebula.
“It is clear that further simulations and modelling will be needed to understand how a substantial population of objects can form below [5 Jupter masses] and how a significant fraction of them can end up in multiple systems,” the team concluded.
The exact mechanisms for how planets go “rogue” are unknown, but several theories exist. The theories include that planets are pulled away from one star by gravitational interactions with other passing stars, or that supernovae kick them out, or that they free float into space after their sun dies.
Alternatively, for the JuMBOs, the researchers speculate that planetary ejections can be caused through planets scattering in a planetary disk or by dynamical interactions between stars.
“The latter are relatively common in dense star-forming regions like the Trapezium Cluster,” the team wrote. “The ensemble of planetary mass objects and JuMBOs that we see in the Trapezium Cluster might arise from a mix of both of these “classical” scenarios, even if both have significant caveats, or perhaps a new, quite separate formation mechanism, such as a fragmentation of a star-less disk, is required.”
Rogue planets are usually impossible to image in visible light, which makes JWST’s sensitive infrared vision the perfect tool to look for them.
This image shows the full survey of the inner Orion Nebula and Trapezium Cluster made using the NIRCam instrument on the NASA/ESA/CSA James Webb Space Telescope. which reveals the nebula, its stars, and many other objects in unprecedented detail in the infrared. Credit: NASA, ESA, CSA / Science leads and image processing: M. McCaughrean, S. Pearson.
The Orion Nebula has been studied for decades to observe the formation and early evolution of stars and other celestial objects. It lies 1,350 light years away from Earth and is visible to the naked eye as a misty smudge at the bottom of the Orion constellation, part of the ‘sword’ of the mythical Greek hunter after whom the constellation is named.
To see the images in detail, see ESA’s ESASky application, which has a user-friendly interface to visualise and download astronomical data. These are among the largest JWST mosaics observed to date.
Orion Nebula in NIRCam short-wavelength channel on ESASky
Orion Nebula in NIRCam long-wavelength channel on ESASky