Controversial 'JuMBO' planets discovered by James Webb telescope may not be an illusion after all

A mysterious new kind of celestial object discovered by the James Webb telescope just inched closer to reality, a new study reports.

Looking within a large stellar nursery in the southern sky, astronomers found two pairs of "rogue" Jupiter-like objects that are similar to mysteriously paired planets that the James Webb Space Telescope (JWST) previously discovered. The planet pairs — which tumble through space, seemingly untethered to any star — dwell in a different part of the Milky Way than JWST's initial discoveries, suggesting that the enigmatic objects truly are a new kind of object. However, further observations are still necessary for confirmation.

"We were always fascinated by the possibility of finding different kinds of planets," Dante Minniti, a professor of astrophysics at the Universidad Andrés Bello University in Chile and co-author of the new research, told Live Science in an email.

Free-floating planets (FFPs) are "rogue" exoplanets that aren't gravitationally bound to a star. These peculiar objects abound in the cosmos. Surveys by space-based telescopes, especially JWST, have revealed hundreds of FFPs in many star-forming regions, or nebulas. NASA estimates that solitary rogue planets may outnumber stars in the Milky Way 20 to 1.

In contrast, binary FFPs — which comprise two rogue exoplanets that orbit each other — seem much rarer. One subset, in particular, has piqued interest. Called Jupiter-mass binary objects, or "JuMBOs," these binary pairs of widely separated planet-like objects measure 0.7 to 30 times Jupiter's mass.

A jumbo-size mystery

In 2023, JWST unveiled 40-odd JuMBO candidates in the Orion Nebula, a stellar nursery in the constellation Orion. Their discovery raised interest because such planet pairs challenged conventional theories of planet formation. Subsequent research, though, disputed their existence, including a 2024 reanalysis that suggested many of the purported planet pairs were actually just distant stars.

Still, these developments didn't dissuade Minniti from searching for more definitive pairs of exoplanets and low-mass cosmic objects. Also on his search list were brown dwarfs, "failed stars" that are more massive than planets but not big enough to be stably powered by nuclear fusion.

However, rather than scouring the Orion Nebula again, Minniti and his collaborators turned to a different stellar nursery: the Lower Centaurus-Crux (LCC) association, which "spreads hundreds of square degrees across the Southern sky," he said.

It consists of more than 100 young, massive blue stars that move together through space but are not linked by gravity. Objects in the LCC association are, on average, about 15 million years old, said Claudio Cáceres, an associate professor of physical sciences at Andrés Bello University and first author of the new study. Exoplanets this age are still considered young, and at longer wavelengths, "they are more luminous than their older counterparts," he wrote in an email to Live Science.

A new type of object?

First, Cáceres and his collaborators created an enormous database of images of the LCC association by crossmatching two datasets. One comprised archival near-infrared photographs by the Visible and Infrared Survey Telescope for Astronomy at the European Southern Observatory's (ESO) Piranal Observatory in Chile. The second dataset consisted of visible-light snapshots gathered by the European Space Agency's Gaia survey.

The researchers searched the data for faint cosmic objects that might be planets. Of the 9,000-odd low-mass candidates they identified, only about 400 actually belonged to the LCC association, since they showed movement patterns that were mathematically predicted. Minniti said the team then "inspected the candidates one by one carefully in order to find faint companions that could be characterized."

Their analysis, described in a study published April 24 in the journal Astronomy & Astrophysics, revealed 17 object binaries. Only two — named VVVX-FFP-001 and VVVX-FFP-007 — are pairs of planet-size objects, and they share several characteristics with JuMBOs.

Both contain two objects, each of which has a mass less than 13 times Jupiter's — approximately 12 and eight times Jupiter's mass for VVVX-FFP-001 and VVVX-FFP-007, respectively. Additionally, both are widely separated; three and 180 times the distance between the sun and Neptune separate VVVX-FFP-001's and VVVX-FFP-007's members, respectively.

Despite these similarities, Cáceres doesn't call the newly discovered objects JuMBOs, noting that the term hasn't been accepted in the research literature. "I personally prefer free-floating planetary-mass binaries," he said.

While the new objects support the existence of JuMBOs, they also suggest that FFP pairs are rare, accounting for just 2% of rogue planets in the LCC association, Cáceres said. Although much smaller than the Orion Nebula JuMBO fraction of 9%, this value agrees with the fraction of paired "cold" objects like brown dwarfs found elsewhere. This suggests the Orion Nebula sample may indeed have falsely identified members.

Additionally, Minniti said, some FFP pairs may be "tight binaries" that orbit each other at narrow separations. He said such planets may retain liquid water because their companions' gravitational tugs heat them up. This could make them habitable, Cáceres said, "even when there is no star. … This is very interesting because these binary planets may transport life through different regions of the Galaxy."

The researchers plan to continue studying the objects using instruments like the ESO's Very Large Telescope. "These observations will help to better characterize the whole sample of low-mass binary objects," Minniti said.