This Planet Smells Funny   
       
   Sept. 13, 2010:  Giant planet GJ 436b in the constellation Leo is missing   
   something.   
       
   Would you believe swamp gas?   
       
   To the surprise of astronomers who have been studying the Neptune-sized planet   
   using NASA's Spitzer Space Telescope, GJ 436b has very little methane (CH4).   
       
   "Methane should be abundant on a planet of this temperature and size, but we   
   found 7000 times less methane than what the models predict," says Kevin   
   Stevenson of the University of Central Florida (UCF). Stevenson was lead   
   author of a paper reporting the result in the April 22, 2010, issue of Nature.   
   [...]   
   An artist's concept of GJ 436b peeking out from behind its parent star, an   
   M-dwarf much cooler than the sun. [larger image]   
       
   The methane deficit is surprising because in our own solar system all gas   
   giants are methane-rich. Hydrogen and carbon are abundant in the atmospheres   
   of Jupiter, Saturn, Uranus and Neptune. These atoms naturally get together to   
   form the simplest hydrocarbon, CH4.   
       
   The example of our local gas giants shaped expectations when Stevenson and   
   colleagues pointed Spitzer in the direction of GJ 436b, only 33 light-years   
   away. Finding methane was a foregone conclusion. But when the researchers   
   analyzed the planet's spectrum, they found little of it. Instead, the   
   atmosphere was rich in carbon monoxide.   
       
   "Actually, it blew our minds," says principal investigator and co-author   
   Joseph Harrington, also of UCF.   
       
   Where did all the methane go? One possibility: it's being broken apart. "UV   
   radiation from the planet's star could be converting the methane into polymers   
   like ethylene," says Harrington. "If you put plastic wrap out in the sun, the   
   UV radiation breaks down the carbon bonds in the plastic, causing it to   
   deteriorate as the long carbon chains break. We propose a similar process on   
   GJ 436b, but there hydrogen atoms split off from methane and let the remnants   
   stick together to make ethylene (C2H4)."   
   [...]   
   A stick-figure diagram of methane. [more] Also, they speculate, strong   
   vertical winds in the planet's atmosphere might be sweeping up material from   
   deep hot layers where carbon monoxide is abundant. CO thus replaces CH4.   
       
   Or it could be something else entirely.   
       
   "This planet's atmosphere could have some sort of alien chemistry going on,"   
   says Harrington. "We just don't know yet."   
       
   Giant planets aren't the only worlds with methane. CH4 is fairly common on   
   Earth, too. Methane forms in the stomachs of cows and goats. It also bubbles   
   up from the bottom of swamps, a byproduct of organic matter decaying in deep   
   mud. On gas giants, methane is just common chemistry, but on our planet, it is   
   a sign of life.   
       
   For this reason, researchers have long planned to look for methane in the   
   atmospheres of distant Earth-sized planets. NASA's Kepler mission is expected   
   to discover many such worlds. Methane floating alongside oxygen could be   
   compelling evidence of biological activity.   
       
   But what if planetary atmospheres don't always follow the rules of our own   
   Solar System? GJ 436b certainty doesn't. Investigators might have to go back   
   to the drawing board and re-figure their chemistry.   
       
   "GJ 436b is telling us something important," says Harrington: "We're not in   
   Kansas anymore."   
       
       
   Authors: Dr. Tony Phillips, Dauna Coulter | Credit: Science@NASA   
       
   More Information   
   Other authors of the Nature paper reporting this result include: Sarah   
   Nymeyer, William C. Bowman, Ryan A. Hardy and Nate B. Lust from the University   
   of Central Florida; Nikku Madhusudhan and Sara Seager of the Massachusetts   
   Institute of Technology, Cambridge; Drake Deming of NASA's Goddard Space   
   Flight Center, Greenbelt, Md.; and Emily Rauscher of Columbia University, New   
   York.   
       
   JPL manages the Spitzer Space Telescope mission for NASA's Science Mission   
   Directorate, Washington. Science operations are conducted at the Spitzer   
   Science Center at Caltech. Caltech manages JPL for NASA.   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.54   
    * Origin: NCS BBS (1:3828/7)