MSGID: 1:317/3 63f6ebe8   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    '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.'    
      
     Date:   
         February 22, 2023   
     Source:   
         Carnegie Institution for Science   
     Summary:   
         Astronomers have 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.   
      
      
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   FULL STORY   
   ==========================================================================   
   A team of astronomers led by Carnegie's Shubham Kanodia has discovered an   
   unusual planetary system in which a large gas giant planet orbits a small   
   red dwarf star called TOI-5205. Their findings which are published in The   
   Astronomical Journal, challenge long-held ideas about planet formation.   
      
      
   ==========================================================================   
   Smaller and cooler than our Sun, M dwarfs are the most common stars in our   
   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.   
      
   The newly discovered planet -- TOI 5205b -- was first identified as   
   a potential candidate by NASA's Transiting Exoplanet Survey Satellite   
   (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 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.   
      
   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.   
      
   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.   
      
   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 Can~as (also of NASA Goddard   
   Space Flight Center), Andrea Lin, Arvind Gupta, Luke Powers, and Lawrence   
   Ramsey; 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   
   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.   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Stars # Extrasolar_Planets # Astronomy # Jupiter #   
                   Eris_(Xena) # Kuiper_Belt # Galaxies # Solar_System   
       * RELATED_TERMS   
             o Extrasolar_planet o Uranus o Eris_(dwarf_planet) o Pluto   
             o Uranus'_natural_satellites o Definition_of_planet o Venus   
             o Saturn   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Carnegie_Institution_for_Science. Note: Content may be edited for style   
   and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Shubham Kanodia, Suvrath Mahadevan, Jessica Libby-Roberts, Gudmundur   
         Stefansson, Caleb I. Can~as, 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, John Wisniewski. TOI-5205b: A Short-period Jovian   
         Planet Transiting a Mid-M Dwarf. The Astronomical Journal, 2023;   
         165 (3): 120 DOI: 10.3847/ 1538-3881/acabce   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230222141146.htm   
      
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