Located at a distance of approximately 285 light-years from our solar system, there exists a beautiful, understated cosmic community. It is anchored by a diminutive, illuminating crimson object named TOI-5205, which serves as the “star” of this community – a red dwarf. As detailed in a recent article published in The Astronomical Journal, we have discovered precisely one planetary companion of TOI-5205 dwelling within the vastness of space.
Scientists have given it the name TOI-5205b, which may sound formal but also has a cute ring to it. This is because it is common for red dwarfs, like TOI-5205, to host planets, often several of them. This is due to the fact that red dwarfs are cooler than the sun, with lower luminosities but much longer lifespans, making them attractive anchors for planets. TOI-5205 has a temperature of around 3,500 Kelvin (3,227 degrees Celsius), which is significantly cooler than our sun’s temperature of 5,800 Kelvin (5,526 degrees Celsius).
However, there are two exceptional characteristics of TOI-5205 and its association with TOI-5205b.
To begin with, it is unexpected for red dwarfs to harbor gas giant planets, yet TOI-5205b does. Moreover, it is generally believed that sunlike stars tend to be accompanied by planets considerably smaller than themselves.
“It is quite astonishing that TOI-5205, a host star only about four times larger than Jupiter, could produce a planet of Jupiter’s size, which defies our current understanding of planet formation,” said Shubham Kanodia, an astronomer at the Carnegie Institute of Science and co-author of the study, in a statement. “According to our presumptive knowledge on planet formation, it is unlikely for TOI-5205b to exist.”
“It’s a planet that’s off-limits.”
For perspective on this difference in size, Kanodia presents a compelling comparison. Consider a Jupiter-sized planet circling a star similar to the sun, like a pea orbiting a grapefruit. However, TOI-5205b orbiting TOI-5205 is more akin to a pea orbiting a lemon.
To clarify, an object of the magnitude of Jupiter cannot be considered small, let alone something that is several times larger than Jupiter. In essence, if you combined the masses of all the planets in our solar system and multiplied the total by two, the resulting chunk would be approximately equal in size to our beloved giant planet.
However, our sun is so massive that it could hold hundreds of Jupiters, whereas only four TOI-5205b’s could fit inside its own star.
A comparison of the size of TOI-5205b in orbit around its host star (left) and in orbit around the sun (right). This image is courtesy of Katherine Cain from the Carnegie Institution for Science.
As for the origin of this peculiar combination of celestial bodies in the TOI-5205 system, we currently do not have a definitive explanation. Kanodia and colleagues have some hypotheses, but they emphasize the importance of further observation to unravel this enigma. The resolution of this mystery may require a reassessment of our understanding of planetary formation theory.
“We acknowledge the existence of TOI-5205 b, indicating a discrepancy in our comprehension of these disks, planetary interiors, or planet formation mechanisms (or alternatively, a combination of all three!),” stated Kanodia in a blog post regarding the breakthrough.
Briefly, when young stars travel through space, they typically carry with them a collection of interstellar gas, rocky debris, and dust known as a disk. According to an accepted theory of planet formation – applicable to gas giants like Jupiter and TOI-5205b – around 10 Earth masses of material from the disk are required to create a rocky planetary core. Following this, a large amount of gas from the disk accumulates around the core and eventually coalesces into giant worlds like the orange-striped icon of our solar system.
However, it’s unlikely that TOI-5205’s original disk contained sufficient building blocks for gas giants to create a planet similar in size to Jupiter. According to Kanodia, “Without enough rocky material in the disk to establish the initial core, the formation of a gas giant planet is impossible at the beginning. Similarly, if the disk vanishes before the massive core is produced, the formation of a gas giant planet is impossible at the end.”
“However,” Kanodia added, “TOI-5205b was created in spite of these constraints.”
Courtesy of the Carnegie Institution for Science, Katherine Cain.
However, on a positive note, the close size ratio between the two celestial bodies in deep space (with TOI-5205b blocking a staggering 7% of the star’s light as viewed from our position) makes them relatively simple to observe and analyze.
The TOI-5205 star system has attracted the attention of researchers, who are keen on exploring its unique origin using the revolutionary James Webb Space Telescope. This telescope is designed to provide a comprehensive view of the universe, and has already made significant discoveries, including the detection of a previously unknown planet, the identification of the chemical composition of a scorching hot planet, and the prospect of possibly discovering the most youthful exoplanet ever recorded – all in just over a year of operation.
Kanodia notes in his blog post that ultimately, the crucial inquiry is: “TOI-5205 b may be an anomaly, but are there other comparable exoplanets in existence? And if so, what is the prevalence of these illicit formations?”
