The pair of Rogues’ Gallery is presented in a set.

There are objects in space that are similar in size to planets and do not revolve around stars. These objects, known as rogue or free-floating planets, are scattered throughout the galaxy like glitter. They can either be created around a star and then expelled, or form on their own from a collapsing gas cloud, resembling a miniature star.

Scientists have recently identified a group of around hundreds of potential rogue planets located in the center of the Orion Nebula. These planets are smaller than previously observed rogue planets and some are even twice the size of Saturn. Interestingly, a large number of these planetary-mass objects are connected to each other in binary pairs, a common characteristic of stars but not typically seen in planets. This discovery suggests that these smaller planets may have formed similarly to stars, despite their size.

The lead researcher, Samuel Pearson, an astronomer at the European Space Agency (ESA) in the Netherlands, inquired about the end of the star formation process and the smallest possible object that can be formed from a gas cloud. Although theoretical estimates have been available for many years, it was not until recently that technology allowed for testing at lower masses.

According to Pearson, it is uncertain if the process of star formation can produce objects as small as planets. If this is indeed possible, it would greatly impact our knowledge of how planets form, the study of stellar astrophysics, and the evolution of galaxies.

Free-Floating Flock

Rogue planets are notoriously difficult to find because they are small and faint. Most have been discovered because they bend the light of a distant star behind them. Some of the youngest rogue planets still radiate a little heat leftover from their formation and can be seen with a high-powered infrared telescope.

Pearson and his co-worker at the European Space Agency, Mark McCaughrean, utilized the James Webb Space Telescope (JWST) to observe the compact core of the Orion Nebula, specifically the Trapezium Cluster of stars. This cluster is estimated to have 2,000 stars and is relatively young, at less than 2 million years old. The researchers hypothesized that any planets that are not orbiting a star would still emit enough light for the JWST to detect them.

The Near Infrared Camera of JWST observed stars and planets hidden in the thick gas clouds of the Orion Nebula. After analyzing the image, the team found 540 potential rogue planets with masses ranging from two times that of Saturn to 13 times that of Jupiter. This discovery is currently being reviewed by peers and was published on a preprint archive in October.

According to Núria Miret Roig, an astrophysicist at the University of Vienna in Austria, the telescope’s exceptional sensitivity and resolution in infrared wavelengths were crucial in facilitating these groundbreaking discoveries.

Measurements of the planets’ motion across the sky, which Miret Roig’s team used to discover a different group of rogues, would help confirm whether these are, in fact, planets. Those measurements are not yet possible for Trapezium because JWST has viewed the region only once, Miret Roig said, but JWST imaged these planets at wavelengths where planets, and not much else, glow bright.

The scientists intend to employ the Near Infrared Spectrograph of JWST to validate whether these entities are planets and assess the composition of their atmospheres.

Jumbo-Sized Mystery

Astronomer Sean Raymond of the Laboratoire d’Astrophysique de Bordeaux in France stated that it is expected for the Trapezium Cluster to have numerous free-floating planets. This is due to the fact that stars in young clusters are in close proximity, increasing the chances of a planet being pulled away from its star through close encounters. Raymond also noted that the discovery’s most intriguing aspect is the presence of binaries.

Out of the 540 objects similar in size to planets that were discovered by the researchers, approximately 9% (or 50) appear to revolve around each other in pairs or trios. While most large stars are found in pairs, it is much less common for small stars and even more so for objects like brown dwarfs. Previous observations of small object pairs have shown them to be orbiting closely together, within a few Earth-Sun distances. However, the team has found a group of Jupiter-sized binary objects, nicknamed JuMBOs, that are on wider orbits and have smaller masses than predicted by binary star theories.

The recent discovery made by JuMBOs adds a new element to the ongoing discussion on the formation of free-floating planets. Raymond, who was not part of the study, stated that the origins of these binaries remain a mystery, although there is a theory that suggests they may have initially formed around stars before being separated by passing stars and eventually becoming wide binaries.

According to Miret Roig, it is unlikely that numerous binary planets could have withstood being separated from their parent stars while still remaining in orbit due to gravity.

According to Miret Roig, it is widely accepted that numerous stars are created in twos. She believes that this is also how binary rogue planets are formed. However, current models are not able to explain this specific situation.

According to Pearson, the nine percent figure is significantly higher than what would typically be seen in planetary-mass systems. It is difficult to justify this with traditional theories of star formation, making it a perplexing observation.

“Kimberly M. S. Cartier, also known as AstroKimCartier, is a writer on our staff.”

Reference: Cartier, K.M.S. (2023). Pairings in the Rogues’ Gallery. Eos, 104, https://doi.org/10.1029/2023EO230417. Published on October 31, 2023.

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