MSGID: 1:317/3 64781f07   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    NIRISS instrument on Webb maps an ultra-hot Jupiter's atmosphere    
      
     Date:   
         May 31, 2023   
     Source:   
         University of Montreal   
     Summary:   
         There's an intriguing exoplanet out there -- 400 light-years   
         out there - - that is so tantalizing that astronomers have been   
         studying it since its discovery in 2009. One orbit for WASP-18 b   
         around its star that is slightly larger than our Sun takes just 23   
         hours. There is nothing like it in our Solar System. A new study   
         about this exoplanet, an ultra-hot gas giant 10 times more massive   
         than Jupiter.   
      
      
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   There's an intriguing exoplanet out there -- 400 light-years out there   
   -- that is so tantalising that astronomers have been studying it since   
   its discovery in 2009. One orbit for WASP-18 b around its star that   
   is slightly larger than our Sun takes just 23 hours. There is nothing   
   like it in our Solar System. A new study led by Universite' de Montre'al   
   Ph.D. student Louis-Philippe Coulombe about this exoplanet, an ultra-hot   
   gas giant 10 times more massive than Jupiter, based on new data from   
   the Canadian NIRISS instrument on the James Webb Space Telescope   
   (JWST) holds many surprises!  Mapping an exoplanet An international   
   team of astronomers have identified water vapor in the atmosphere of   
   the exoplanet WASP-18 b and made a temperature map of the planet as it   
   slipped behind, and reappeared from, its star. This event is known as   
   a secondary eclipse. Scientists can read the combined light from the   
   star and planet, then refine the measurements from just the star as the   
   planet moves behind it.   
      
   The same side, known as the dayside, of WASP-18 b always faces its star,   
   just as the same side of the Moon always faces Earth. This is called   
   tidal locking.   
      
   The temperature, or brightness, map of the exoplanet shows a huge change   
   in temperature -- up to 1,000 degrees -- from the hottest point facing the   
   star to the terminator, where day and night sides of the tidally-locked   
   planet meet in permanent twilight.   
      
   ''JWST is giving us the sensitivity to make much more detailed maps of   
   hot giant planets like WASP-18 b than ever before. This is the first time   
   a planet has been mapped with JWST, and it's really exciting to see that   
   some of what our models predicted, such as a sharp drop in temperature   
   away from the point on the planet directly facing the star, is actually   
   seen in the data!'' said Megan Mansfield, a Sagan Fellow at the University   
   of Arizona, and one of the authors of the paper describing the results.   
      
   The team mapped temperature gradients across the day side of the   
   planet. Given how much cooler the planet is at the terminator, there is   
   likely something hindering winds from efficiently redistributing heat   
   to the night side. But what is affecting the winds is still a mystery.   
      
   ''The brightness map of WASP-18 b shows a lack of east-west winds that is   
   best matched by models with atmospheric drag. One possible explanation   
   is that this planet has a strong magnetic field, which would be an   
   exciting discovery!''  said co-author Ryan Challener, of the University   
   of Michigan.   
      
   One interpretation of the eclipse map is that magnetic effects force the   
   winds to blow from the planet's equator up over the North pole and down   
   over the South pole, instead of East-West, as we would otherwise expect.   
      
   Researchers recorded temperature changes at different elevations of the   
   gas giant planet's layers of atmosphere. They saw temperatures increase   
   with elevation, varying by hundreds of degrees.   
      
   Signs of water vapor The spectrum of the planet's atmosphere clearly   
   shows multiple small but precisely measured water features, present   
   despite the extreme temperatures of almost 2,700 degrees Celsius. It is   
   so hot that it would tear most water molecules apart, so still seeing its   
   presence speaks to Webb's extraordinary sensitivity to detect remaining   
   water. The amounts recorded in WASP-18 b's atmosphere indicate water   
   vapor is present at various elevations ''It was a great feeling to look   
   at WASP-18 b's JWST spectrum for the first time and see the subtle but   
   precisely measured signature of water,'' said Louis-Philippe Coulombe,   
   a Ph.D. student at the Universite' de Montre'al, member of the Trottier   
   Institute for Research on Exoplanets (iREx) and lead author of the WASP-18   
   b paper. ''Using this kind of measurements, we will be able to detect   
   such molecules for a wide range of planets in the years to come!'',   
   added Bjo"rn Benneke, UdeM Professor, iREx member and co-author of this   
   paper. Benneke is Coulombe's Ph.D. advisor as well and has been leading   
   worldwide efforts to study WASP-18 b since 2016.   
      
   The work of the NIRISS instrument and early career scientists The team   
   of astronomers observed WASP-18 b for about six hours using one of Webb's   
   instruments, the Near-Infrared Imager and Slitless Spectrograph (NIRISS),   
   contributed by the Canadian Space Agency and several partners including   
   the Universite' de Montre'al and iREx.   
      
   ''Because the water features in this spectrum are so subtle, they were   
   difficult to identify in previous observations. That made it really   
   exciting to finally see water features with these JWST observations,''   
   said Anjali Piette, a postdoctoral fellow at the Carnegie Institution   
   for Science and one of the authors of the new research.   
      
   The WASP-18 b observations were collected as part of the Transiting   
   Exoplanet Community Early Release Science Program led by Natalie Batalha,   
   an astronomer at the University of California, Santa Cruz, who helped   
   coordinate the new research and the more than one hundred researchers   
   in the team. Much of this ground-breaking work is being done by early   
   career scientists like Coulombe, Challener, Piette, and Mansfield.   
      
   Proximity, both to its star and to us, helped make WASP-18 b   
   such an intriguing target for these scientists, as did its large   
   mass. WASP-18 b is one of the most massive worlds whose atmospheres we   
   can investigate. Astronomers are striving to understand how such planets   
   form and come to be where they are in their systems. This, too, has some   
   early answers from Webb.   
      
   ''By analysing WASP-18 b's spectrum, we not only learn about the various   
   molecules that can be found in its atmosphere but also about the way   
   it formed.   
      
   We find from our observations that WASP-18 b's composition is very   
   similar to that of its star, meaning it most likely formed from the   
   leftover gas that was present just after the star was born,'' Coulombe   
   said. ''Those results are very valuable to get a clear picture of how   
   strange planets like WASP-18 b, which have no counterpart in our Solar   
   System, come to exist.''   
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Extrasolar_Planets # Astronomy # Stars # Jupiter #   
                   Kuiper_Belt # Pluto # Eris_(Xena) # Solar_System   
       * RELATED_TERMS   
             o Jupiter o Extrasolar_planet o Light-year o Planet o   
             Blue_supergiant_star o Definition_of_planet o Red_giant o Saturn   
      
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   Story Source: Materials provided by University_of_Montreal. Note:   
   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. LP., Benneke, B., Challener, R. et al. A broadband thermal emission   
         spectrum of the ultra-hot Jupiter WASP-18b. Nature, 2023 DOI:   
         10.1038/ s41586-023-06230-1   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230531150101.htm   
      
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