Astronomers led by Shubham Kanodia of Carnegie have identified a peculiar planetary system in which a huge gas giant planet revolves around a dim red dwarf star known as TOI-5205. This research, which was published in The Astronomical Journal, casts doubt on conventional wisdom regarding planet formation.
The most prevalent stars in our Milky Way galaxy are M dwarfs, which are smaller and cooler than our sun. These stars are typically much redder and half as hot as the sun due to their small size. They have incredibly lengthy lifespans while having very low luminosities.
Red dwarfs typically host more planets than other, more massive types of stars, but due to their development histories, they are unlikely to harbor gas giants.
NASA’s Transiting Exoplanet Survey Satellite (TESS) first identified the newly discovered planet TOI 5205b as a potential candidate. Kanodia’s team, which included Carnegie’s Anjali Piette, Alan Boss, Johanna Teske, and John Chambers, then confirmed its planetary nature and characterized it using a variety of ground-based instruments and facilities.
“The host star, TOI-5205, is just about four times the size of Jupiter, yet it has somehow managed to form a Jupiter-sized planet, which is quite surprising,” exclaimed Kanodia, who specializes in studying these stars, which comprise nearly three-quarters of our galaxy yet can’t be seen with the naked eye.
In the beginning, if there isn’t enough rocky material in the disk to form the initial core, then one cannot form a gas giant planet. And at the end, if the disk evaporates away before the massive core is formed, then one cannot form a gas giant planet. And yet TOI-5205b formed despite these guardrails. Based on our nominal current understanding of planet formation, TOI-5205b should not exist; it is a ‘forbidden’ planet.
Shubham Kanodia
A few gas giants have been found in orbit around older M dwarf stars. Yet up to this point, there hasn’t been a gas giant discovered in a planetary system with a low-mass M dwarf like TOI-5205.
A Jupiter-like planet orbiting a sun-like star may be compared to a pea circling a grapefruit; with TOI-5205b, however, the host star is so much smaller that a pea circling a lemon would be more appropriate.
In fact, one of the greatest known exoplanet transits occurs when the Jupiter-mass TOI 5205b passes in front of its host and blocks nearly 7% of its light.
Planets are born in the rotating disk of gas and dust that surrounds young stars. According to the most popular idea, this rocky material must first build up to the size of around 10 Earth masses to form a gigantic rocky core, which then quickly scavenges large quantities of gas from nearby portions of the disk to create the giant planet we see today.
The time frame in which this happens is crucial.
“TOI-5205b’s existence stretches what we know about the disks in which these planets are born,” Kanodia explained. “In the beginning, if there isn’t enough rocky material in the disk to form the initial core, then one cannot form a gas giant planet. And at the end, if the disk evaporates away before the massive core is formed, then one cannot form a gas giant planet. And yet TOI-5205b formed despite these guardrails. Based on our nominal current understanding of planet formation, TOI-5205b should not exist; it is a ‘forbidden’ planet.”
The scientists showed that the planet’s very wide transit depth makes it incredibly favorable for subsequent studies with the recently launched JWST, which could clarify its atmosphere and provide some additional hints regarding the enigma of its genesis.
The TESS follow-up research was conducted using the Habitable-zone Planet Finder (HPF; Texas, US) and Low Resolution Spectrograph (LRS2; Texas, US) on the 10-m Hobby Eberly Telescope, the ARCTIC camera on the 3.5-m Apache Point Observatory (APO; New Mexico, US), the NN-Explore Exoplanet Stellar Speckle Imager (NESSI, Arizona, US) at the 3.5-m WIYN telescope, the 0.6-m Red Buttes Observatory (RBO, Wyoming, US), and the 0.3 m Three Hundred Millimeter Telescope (TMMT, Chile).
