MSGID: 1:317/3 649d08ee   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Life after death: Astronomers find a planet that shouldn't exist    
      
     Date:   
         June 28, 2023   
     Source:   
         University of Hawaii at Manoa   
     Summary:   
         The star would have inflated up to 1.5 times the planet's orbital   
         distance -- engulfing the planet in the process -- before shrinking   
         to its current size at only one-tenth of that distance.   
      
      
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   FULL STORY   
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   When our Sun reaches the end of its life, it will expand to 100 times its   
   current size, enveloping the Earth. Many planets in other solar systems   
   face a similar doom as their host stars grow old. But not all hope is   
   lost, as astronomers from the University of Hawaii Institute for Astronomy   
   (UH IfA) have made the remarkable discovery of a planet's survival after   
   what should have been certain demise at the hands of its sun.   
      
   The Jupiter-like planet 8 UMi b, officially named Halla, orbits the red   
   giant star Baekdu (8 UMi) at only half the distance separating the Earth   
   and the Sun.   
      
   Using two Maunakea Observatories on Hawaiii Island -- W. M. Keck   
   Observatory and Canada-France-Hawaii Telescope (CFHT) -- a team   
   of astronomers led by Marc Hon, a NASA Hubble Fellow at UH IfA, has   
   discovered that Halla persists despite the normally perilous evolution of   
   Baekdu. Using observations of Baekdu's stellar oscillations from NASA's   
   Transiting Exoplanet Survey Satellite (TESS), they found that the star   
   is burning helium in its core, signaling that it had already expanded   
   enormously into a red giant star once before.   
      
   The star would have inflated up to 1.5 times the planet's orbital   
   distance - - engulfing the planet in the process -- before shrinking to   
   its current size at only one-tenth of that distance.   
      
   The study is published in today's issue of the journal Nature.   
      
   "Planetary engulfment has catastrophic consequences for either the   
   planet or the star itself -- or both. The fact that Halla has managed   
   to persist in the immediate vicinity of a giant star that would have   
   otherwise engulfed it highlights the planet as an extraordinary survivor,"   
   said Hon, the lead author of the study.   
      
   Maunakea Observatories Confirm the Survivor The planet Halla was   
   discovered in 2015 by a team of astronomers from Korea using the radial   
   velocity method, which measures the periodic movement of a star due to   
   the gravitational tug of the orbiting planet. Following the discovery   
   that the star must at one time have been larger than the planet's orbit,   
   the IfA team conducted additional observations from 2021-2022 using Keck   
   Observatory's High-Resolution Echelle Spectrometer (HIRES) and CFHT's   
   ESPaDOnS instrument. These new data confirmed the planet's 93-day,   
   nearly circular orbit had remained stable for over a decade and that   
   the radial velocity changes must be due to a planet.   
      
   "Together, these observations confirmed the existence of the planet,   
   leaving us with the compelling question of how the planet actually   
   survived," said IfA astronomer Daniel Huber, second author of the   
   study. "The observations from multiple telescopes on Maunakea was   
   critical in this process."  Escaping Engulfment At a distance of 0.46   
   astronomical units (AU, or the Earth-Sun distance) to its star, the   
   planet Halla resembles 'warm' or 'hot' Jupiter-like planets that are   
   thought to have started on larger orbits before migrating inward close to   
   their stars. However, in the face of a rapidly evolving host star, such   
   an origin becomes an extremely unlikely survival pathway for planet Halla.   
      
   Another theory for the planet's survival is that it never faced the   
   danger of engulfment. Similar to the famous planet Tatooine from Star   
   Wars, which orbits two suns, the team believes the host star Baekdu may   
   have originally been two stars. A merger of these two stars may have   
   prevented any one of them from expanding sufficiently large enough to   
   engulf the planet.   
      
   A third possibility is that Halla is a relative newborn -- that the   
   violent collision between the two stars produced a gas cloud from which   
   the planet formed. In other words, the planet Halla may be a recently-born   
   'second generation' planet.   
      
   "Most stars are in binary systems, but we don't yet fully grasp how   
   planets may form around them. Therefore, it's plausible that more   
   planets may actually exist around highly evolved stars thanks to binary   
   interactions," explained Hon.   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Extrasolar_Planets # Stars # Astronomy # Jupiter #   
                   Kuiper_Belt # Eris_(Xena) # Mars # Pluto   
       * RELATED_TERMS   
             o Venus o Eris_(dwarf_planet) o Precession o Uranus o Axial_tilt   
             o Moon o Neptune o Definition_of_planet   
      
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   Story Source: Materials provided by University_of_Hawaii_at_Manoa. Note:   
   Content may be edited for style and length.   
      
      
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   Related Multimedia:   
       * Artist's_impression_of_the_planet's_survival   
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   Journal Reference:   
      1. Marc Hon, Daniel Huber, Nicholas Z. Rui, Jim Fuller, Dimitri   
      Veras, James   
         S. Kuszlewicz, Oleg Kochukhov, Amalie Stokholm, Jakob Lysgaard   
         Ro/rsted, Mutlu Yıldız, Zeynep C,elik Orhan, Sibel O"rtel,   
         Chen Jiang, Daniel R. Hey, Howard Isaacson, Jingwen Zhang, Mathieu   
         Vrard, Keivan G.   
      
         Stassun, Benjamin J. Shappee, Jamie Tayar, Zachary R. Claytor,   
         Corey Beard, Timothy R. Bedding, Casey Brinkman, Tiago L. Campante,   
         William J.   
      
         Chaplin, Ashley Chontos, Steven Giacalone, Rae Holcomb, Andrew   
         W. Howard, Jack Lubin, Mason MacDougall, Benjamin T. Montet, Joseph   
         M. A. Murphy, Joel Ong, Daria Pidhorodetska, Alex S. Polanski,   
         Malena Rice, Dennis Stello, Dakotah Tyler, Judah Van Zandt,   
         Lauren M. Weiss. A close-in giant planet escapes engulfment by its   
         star. Nature, 2023; 618 (7967): 917 DOI: 10.1038/s41586-023-06029-0   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230628130343.htm   
      
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