25 June 2004
Photos Of Planets Outside Our Solar System Soon
by Kate Melville
An astronomer from the University of Arizona is using a novel camera to hunt for extrasolar planets. The camera has already made stunning images of Saturn's moon, Titan, and discovered an object just 27 times the mass of Jupiter. They hope the camera will be the first to directly photograph faint gas-giants similar to Jupiter in solar systems beyond our own.
Professor Laird M. Close and graduate students Beth Biller and Eric Nielsen, will use Close's custom SDI (Simultaneous Differential Imager) cameras on two big telescopes in Arizona and Chile to hunt for planets orbiting other stars. Astronomers have indirectly detected more than 100 planets circling stars in other solar systems, but none have yet been directly imaged.
Close plans to solve the problem of detecting faint planets near their billion-times-brighter stars by using a unique, high-contrast, SDI camera. The camera uses adaptive optics, which remove the blurring effects of the Earth's atmosphere and produce extremely sharp images.
The SDI camera splits light from a single object into four identical images, then passes the resulting beams through four slightly different methane-sensitive filters. When the filtered light beams hit the detector array, astronomers can subtract the images so the bright star disappears, revealing the massive, methane-rich planet.
Professor Close and his collaborators will use SDI to examine 100 young northern and southern hemisphere stars that are near Earth. They will hunt for planets as small as 3 Jupiter masses that are as close as 5 AU from their stars. This is about the distance between Jupiter and the sun. One "AU," or astronomical unit, is the distance between Earth and the sun.
The northern SDI camera will be used on the 6.5-meter, UA/Smithsonian, MMT telescope on Mount Hopkins, Ariz, in collaboration with Steward Observatory astronomer Donald McCarthy. The southern SDI camera has been installed at the European Southern Observatory's (ESO) 8.2-meter Very Large Telescope (VLT) in Chile.
"Our imaging technique should be about 100 times more sensitive than current imaging technologies," Close said. "This will allow us to directly detect sub-stellar companions to nearby stars. It also will allow us to look for planets in regions where we have not been able to search before but that are likely to be rich with massive planets," he added. "If we find such planets, they can help tell us if those stars have Earth-like planets."
In collaboration with Mark McCaughrean of the Astrophysical Institute Potsdam, Close and his German colleagues discovered a 27 Jupiter mass object named Epsilon Indi Bb the first night they used the camera. They reported the finding in the journal Astronomy & Astrophysics.
Epsilon Indi Bb is a methane-rich object a mere 12 light years from the sun and just 2.6 AU away from a 43 Jupiter-mass object, called Epsilon Indi Ba, that McCaughrean and others reported in another paper in 2003.
"Although a bit too massive to be a true planet, Epsilon Indi Bb is just slightly hotter than a convection oven," Close said. "It is the coolest, closest binary 'brown dwarf' ever imaged."
Brown dwarfs are too small to shine like a star but too big to be called planets.
"This discovery will play an important role in understanding the nature and physics of brown dwarfs," Close said.
Last February, during commissioning of the SDI camera in Chile, Hartung, Close and their European colleagues produced the sharpest images ever taken of Saturn's largest moon, Titan.