Earth's Dust Tail Points to Alien Planets   
       
   November 12, 2010:  Did you know that the Earth has a dust tail? The Spitzer   
   Space Telescope sailed right through it a few months ago, giving researchers a   
   clear idea of what it looks like. That could be a big help to planet hunters   
   trying to track down alien worlds.   
   [...]   
   An artist's concept of Spitzer passing through Earth's dusty tail. [more]     
   "Planets in distant solar systems probably have similar dust tails," says   
   Spitzer project scientist Mike Werner. "And in some circumstances these dust   
   features may be easier to see than the planets themselves. So we need to know   
   how to recognize them."   
       
   It's extremely challenging - and usually impossible - to directly image   
   exoplanets. They're relatively small and faint, hiding in the glare of the   
   stars they orbit.   
       
   "A dust tail like Earth's could produce a bigger signal than a planet does.   
   And it could alert researchers to a planet too small to see otherwise."   
       
   Earth has a dust tail not because the planet itself is particularly dusty, but   
   rather because the whole solar system is. Interplanetary space is littered   
   with dusty fragments of comets and colliding asteroids. When Earth orbits   
   through this dusty environment, a tail forms in the rear, akin to swaths of   
   fallen leaves swirling up behind a streetsweeper.   
       
   "As Earth orbits the sun, it creates a sort of shell or depression that dust   
   particles fall into, creating a thickening of dust - the tail - that Earth   
   pulls along via gravity," explains Werner. "In fact, the tail trails our   
   planet all the way around the sun, forming a large dusty ring."   
   [...]   
   A computer simulation of Earth's dust tail/ring seen from a vantage point   
   outside our solar system. Colors indicate density; purple is lowest, red is   
   highest. Credit: Christopher Stark, GSFC [larger image]   
       
   Spitzer's recent observations have helped astronomers map the structure of   
   Earth's dust tail and figure out what similar "tell-tale tails" attached to   
   alien planets might look like.   
       
   Like our own solar system, other planetary systems are infused with dust that   
   forms a dusty disk encircling the central star. And like Earth, exoplanets   
   interact with their dust disk gravitationally, channeling and drawing strange   
   features into it.   
       
   "In some stars' dust disks there are bumps, warps, rings, and offsets telling   
   us that planets are interacting with the dust," explains Mark Clampin of   
   NASA's Goddard Space Flight Center. "So we can 'follow the dust' to the   
   planets. So far, we've seen about 20 dust disks in other solar systems. And in   
   some of those cases, following the dust has already paid off."   
       
   Clampin, Paul Kalas, and colleagues were looking for a planet around the   
   bright southern star Fomalhaut when they unexpectedly found a dust ring. The   
   shape of that ring led them to their goal. "We suspected that the ring's sharp   
   inner edge was formed by a planet gravitationally clearing out the surrounding   
   debris," says Clampin. "We tracked the planet by this 'footprint' in the   
   dust." (See the footprint here.)   
       
   Another Hubble image shows a dusty disk around Beta Pictoris, a star in the   
   constellation Pictor, or "Painter's Easel," pictured below:   
   [...]   
   A Hubble image of dusty material circling the star Beta Pictoris. [more]   
       
   "Note the smaller dust ring that's tilted with respect to the larger dust   
   disk," says Clampin. "Like Earth, this planet is shepherding the dust into its   
   orbital plane."   
       
   Clampin and Werner say Spitzer's observation of Earth's dust tail and these   
   initial observations of dust structures in distant solar systems set the stage   
   for the planet hunting debut of the James Webb Space Telescope. They fully   
   expect the huge and powerful new telescope to spot many tell-tale tails ... of   
   the alien variety.   
       
       
   Author: Dauna Coulter | Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   (1) Clampin explains why it's hard to see the Earth's dust tail from within   
   our solar system: "Imagine looking at fog on the Golden gate from above where   
   you can clearly see the structure. If, on the other hand, you are standing on   
   the bridge, it's a lot harder to discern the shape of the cloud."   
       
   (2) NASA's James Webb Space Telescope, targeted to launch in 2014, is a large,   
   infrared-optimized space telescope. For more information, see ht   
   p://www.jwst.nasa.gov/   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.56   
    * Origin: NCS BBS (1:3828/7)