MSGID: 1:317/3 6448a8f1   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Asteroid's comet-like tail Is not made of dust, solar observatories   
   reveal    
      
     Date:   
         April 25, 2023   
     Source:   
         NASA/Goddard Space Flight Center   
     Summary:   
         We have known for a while that asteroid 3200 Phaethon acts like   
         a comet.   
      
         It brightens and forms a tail when it's near the Sun, and it is   
         the source of the annual Geminid meteor shower, even though comets   
         are responsible for most meteor showers. Scientists had blamed   
         Phaethon's comet-like behavior on dust escaping from the asteroid   
         as it's scorched by the Sun. However, a new study using two NASA   
         solar observatories reveals that Phaethon's tail is not dusty at   
         all but is actually made of sodium gas.   
      
      
         Facebook Twitter Pinterest LinkedIN Email   
      
   ==========================================================================   
   FULL STORY   
   ==========================================================================   
   A weird asteroid has just gotten a little weirder.   
      
   We have known for a while that asteroid 3200 Phaethon acts like a   
   comet. It brightens and forms a tail when it's near the Sun, and it is   
   the source of the annual Geminid meteor shower, even though comets are   
   responsible for most meteor showers. Scientists had blamed Phaethon's   
   comet-like behavior on dust escaping from the asteroid as it's scorched   
   by the Sun. However, a new study using two NASA solar observatories   
   reveals that Phaethon's tail is not dusty at all but is actually made   
   of sodium gas.   
      
   "Our analysis shows that Phaethon's comet-like activity cannot be   
   explained by any kind of dust," said California Institute of Technology   
   PhD student Qicheng Zhang, who is the lead author of a paper published   
   in the Planetary Science Journal reporting the results.   
      
   Asteroids, which are mostly rocky, do not usually form tails when   
   they approach the Sun. Comets, however, are a mix of ice and rock,   
   and typically do form tails as the Sun vaporizes their ice, blasting   
   material off their surfaces and leaving a trail along their orbits. When   
   Earth passes through a debris trail, those cometary bits burn up in our   
   atmosphere and produce a swarm of shooting stars -- a meteor shower.   
      
   After astronomers discovered Phaethon in 1983, they realized that the   
   asteroid's orbit matched that of the Geminid meteors. This pointed to   
   Phaethon as the source of the annual meteor shower, even though Phaethon   
   was an asteroid and not a comet.   
      
   In 2009, NASA's Solar Terrestrial Relations Observatory (STEREO)   
   spotted a short tail extending from Phaethon as the asteroid reached   
   its closest point to the Sun (or "perihelion") along its 524-day   
   orbit. Regular telescopes hadn't seen the tail before because it only   
   forms when Phaethon is too close to the Sun to observe, except with   
   solar observatories. STEREO also saw Phaethon's tail develop on later   
   solar approaches in 2012 and 2016. The tail's appearance supported the   
   idea that dust was escaping the asteroid's surface when heated by the Sun.   
      
   However, in 2018, another solar mission imaged part of the Geminid debris   
   trail and found a surprise. Observations from NASA's Parker Solar Probe   
   showed that the trail contained far more material than Phaethon could   
   possibly shed during its close approaches to the Sun.   
      
   Zhang's team wondered whether something else, other than dust, was behind   
   Phaethon's comet-like behavior. "Comets often glow brilliantly by sodium   
   emission when very near the Sun, so we suspected sodium could likewise   
   serve a key role in Phaethon's brightening," Zhang said.   
      
   An earlier study, based on models and lab tests, suggested that the   
   Sun's intense heat during Phaethon's close solar approaches could indeed   
   vaporize sodium within the asteroid and drive comet-like activity.   
      
   Hoping to find out what the tail is really made of, Zhang looked for it   
   again during Phaethon's latest perihelion in 2022. He used the Solar and   
   Heliospheric Observatory (SOHO) spacecraft -- a joint mission between   
   NASA and the European Space Agency (ESA) -- which has color filters that   
   can detect sodium and dust.   
      
   Zhang's team also searched archival images from STEREO and SOHO, finding   
   the tail during 18 of Phaethon's close solar approaches between 1997   
   and 2022.   
      
   In SOHO's observations, the asteroid's tail appeared bright in the filter   
   that detects sodium, but it did not appear in the filter that detects   
   dust. In addition, the shape of the tail and the way it brightened as   
   Phaethon passed the Sun matched exactly what scientists would expect if   
   it were made of sodium, but not if it were made of dust.   
      
   This evidence indicates that Phaethon's tail is made of sodium, not dust.   
      
   "Not only do we have a really cool result that kind of upends 14   
   years of thinking about a well-scrutinized object," said team member   
   Karl Battams of the Naval Research Laboratory, "but we also did this   
   using data from two heliophysics spacecraft -- SOHO and STEREO -- that   
   were not at all intended to study phenomena like this."  Zhang and his   
   colleagues now wonder whether some comets discovered by SOHO - - and by   
   citizen scientists studying SOHO images as part of the Sungrazer Project   
   -- are not comets at all.   
      
   "A lot of those other sunskirting 'comets' may also not be 'comets'   
   in the usual, icy body sense, but may instead be rocky asteroids like   
   Phaethon heated up by the Sun," Zhang explained.   
      
   Still, one important question remains: If Phaethon doesn't shed much   
   dust, how does the asteroid supply the material for the Geminid meteor   
   shower we see each December?  Zhang's team suspects that some sort of   
   disruptive event a few thousand years ago -- perhaps a piece of the   
   asteroid breaking apart under the stresses of Phaethon's rotation --   
   caused Phaethon to eject the billion tons of material estimated to make   
   up the Geminid debris stream. But what that event was remains a mystery.   
      
   More answers may come from an upcoming Japan Aerospace Exploration Agency   
   (JAXA) mission called DESTINY+ (short for Demonstration and Experiment   
   of Space Technology for Interplanetary voyage Phaethon fLyby and dUst   
   Science). Later this decade, the DESTINY+ spacecraft is expected to   
   fly past Phaethon, imaging its rocky surface and studying any dust that   
   might exist around this enigmatic asteroid.   
      
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Asteroids,_Comets_and_Meteors # Sun # Solar_Flare #   
                   Astronomy # NASA # Space_Exploration # Space_Missions   
                   # Solar_System   
       * RELATED_TERMS   
             o Comet o Asteroid o Comet_Shoemaker-Levy_9 o Comet_Hale-Bopp   
             o Solar_system o Impact_crater o Asteroid_belt o Meteor   
      
   ==========================================================================   
   Story Source: Materials provided by   
   NASA/Goddard_Space_Flight_Center. Original written by Vanessa   
   Thomas. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Related Multimedia:   
       * Asteroid_Phaethon   
   ==========================================================================   
   Journal Reference:   
      1. Qicheng Zhang, Karl Battams, Quanzhi Ye, Matthew M. Knight, Carl A.   
      
         Schmidt. Sodium Brightening of (3200) Phaethon near Perihelion. The   
         Planetary Science Journal, 2023; 4 (4): 70 DOI: 10.3847/PSJ/acc866   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/04/230425111159.htm   
      
   --- up 1 year, 8 weeks, 1 day, 10 hours, 50 minutes   
    * Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)   
   SEEN-BY: 15/0 106/201 114/705 123/120 153/7715 218/700 226/30 227/114   
   SEEN-BY: 229/110 112 113 307 317 400 426 428 470 664 700 292/854 298/25   
   SEEN-BY: 305/3 317/3 320/219 396/45   
   PATH: 317/3 229/426