Artist’s conception of a large gas giant planet orbiting a small red dwarf star called TOI-5205. Credit: Image by Katherine Cain, courtesy of the Carnegie Institution for Science
“Forbidden” Planet Orbiting Small Star Challenges Gas Giant Formation Theories
Based on our current understanding of planet formation, TOI-5205b should not exist; it is a “forbidden” planet.
A team of astronomers has discovered an unusual planetary system in which a large gas giant planet orbits a small red dwarf star called TOI-5205. Their findings challenge long-held ideas about planet formation. Led by Shubham Kanodia from the Carnegie Institution for Science, the researchers published their findings in The Astronomical Journal.
Smaller and cooler than our Sun, M dwarfs are the most common stars in our Milky WayThe Milky Way is the galaxy that contains our Solar System and is part of the Local Group of galaxies. It is a barred spiral galaxy that contains an estimated 100-400 billion stars and has a diameter between 150,000 and 200,000 light-years. The name "Milky Way" comes from the appearance of the galaxy from Earth as a faint band of light that stretches across the night sky, resembling spilled milk.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Milky Way galaxy. Due to their small size, these stars tend to be about half as hot as the Sun and much redder. They have very low luminosities, but extremely long lifespans. Although red dwarfs host more planets, on average, than other, more massive types of stars, their formation histories make them unlikely candidates to host gas giants.
Artist’s conception of a large gas giant planet orbiting a small red dwarf star called TOI-5205. Until now no gas giant has been found in a planetary system around a low-mass M dwarf like TOI-5205. Credit: Image by Katherine Cain, courtesy of the Carnegie Institution for Science
The newly discovered planet—TOI 5205b—was first identified as a potential candidate by NASA’s Transiting Exoplanet Survey Satellite (TESSLaunched on April 18, 2018, aboard a SpaceX Falcon 9 rocket, NASA’s Transiting Exoplanet Survey Satellite (TESS) is a space telescope mission to search nearby stars for undiscovered worlds with a goal of discovering thousands of exoplanets around nearby bright stars.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>TESS). 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 JupiterJupiter is the largest planet in the solar system and the fifth planet from the sun. It is a gas giant with a mass greater then all of the other planets combined. Its name comes from the Roman god Jupiter.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>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. He also wrote a blog post about the discovery.
A small number of gas giants have been discovered orbiting older M dwarf stars. But until now no gas giant has been found in a planetary system around a low-mass M dwarf like TOI-5205. To grasp the size comparison here, a Jupiter-like planet orbiting a Sun-like star could be compared to a pea going around a grapefruit; for TOI-5205b, because the host star is so much smaller, it is more like a pea going around a lemon. In fact, when the Jupiter-mass TOI 5205b crosses in front of its host, it blocks about seven percent of its light—one of the largest known exoplanet transits.
A Jupiter-like planet orbiting a Sun-like star could be compared to a pea going around a grapefruit; for TOI-5205b, because the host star is so much smaller, it is more like a pea going around a lemon, said lead author Shubham Kanodia. Credit: Artwork by Katherine Cain is courtesy of the Carnegie Institution for Science
Planets are born in the rotating disk of gas and dust that surrounds young stars. The most commonly used theory of gas planet formation requires about 10 Earth masses of this rocky material to accumulate and form a massive rocky core, after which it rapidly sweeps up large amounts of gas from the neighboring regions of the disk to form 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 team demonstrated that the planet’s very large transit depth makes it extremely conducive for future observations with the recently launched JWST, which could shed some light on its atmosphere and offer some additional clues about the mystery of its formation.
Reference: “TOI-5205b: A Short-period Jovian Planet Transiting a Mid-M Dwarf” by Shubham Kanodia, Suvrath Mahadevan, Jessica Libby-Roberts, Gudmundur Stefansson, Caleb I. Cañas, Anjali A. A. Piette, Alan Boss, Johanna Teske, John Chambers, Greg Zeimann, Andrew Monson, Paul Robertson, Joe P. Ninan, Andrea S. J. Lin, Chad F. Bender, William D. Cochran, Scott A. Diddams, Arvind F. Gupta, Samuel Halverson, Suzanne Hawley, Henry A. Kobulnicky, Andrew J. Metcalf, Brock A. Parker, Luke Powers, Lawrence W. Ramsey, Arpita Roy, Christian Schwab, Tera N. Swaby, Ryan C. Terrien and John Wisniewski, 21 February 2023, The Astronomical Journal.
DOI: 10.3847/1538-3881/acabce
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).
Other members of the research team were: Penn State University’s Suvrath Mahadevan, Jessica Libby-Roberts, Caleb Cañas (also of NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. Its vision is "To discover and expand knowledge for the benefit of humanity." Its core values are "safety, integrity, teamwork, excellence, and inclusion." NASA conducts research, develops technology and launches missions to explore and study Earth, the solar system, and the universe beyond. It also works to advance the state of knowledge in a wide range of scientific fields, including Earth and space science, planetary science, astrophysics, and heliophysics, and it collaborates with private companies and international partners to achieve its goals.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>NASA Goddard Space Flight Center), Andrea Lin, Arvind Gupta, Luke Powers, and Lawrence Ramsey; Princeton UniversityFounded in 1746, Princeton University is a private Ivy League research university in Princeton, New Jersey and the fourth-oldest institution of higher education in the United States. It provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences, and engineering.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Princeton University’s Gudmundur Stefansson; University of Texas Austin’s Greg Zeimann and William Cochran; University of Arizona’s Andrew Monson and Chad Bender; UC Irvine’s Paul Robertson; the Tata Institute of Fundamental Research’s Joe Ninan; University of Colorado Boulder’s Scott Diddams; the Jet Propulsion Laboratory’s Samuel Halverson; University of WashingtonFounded in 1861, the University of Washington (UW, simply Washington, or informally U-Dub) is a public research university in Seattle, Washington, with additional campuses in Tacoma and Bothell. Classified as an R1 Doctoral Research University classification under the Carnegie Classification of Institutions of Higher Education, UW is a member of the Association of American Universities.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>University of Washington’s Suzanne Hawley; University of Wyoming’s Henry Kobulnicky, Brock Parker, and Tera Swaby; the Air Force Research Laboratory’s Andrew Metcalf; the Space Telescope Science Institute’s Arpita Roy (also of Johns Hopkins University); Macquarie University’s Christian Schwab; Carleton College’s Ryan Terrien; and George Mason University’s John Wisniewski.
Source: SciTechDaily
