Far away: Image depicts the distance of the Oort Cloud from the Solar System using a logarithmic scale.
Credit: NASA
SYDNEY: Subtle variations in the cosmic microwave radiation left over from the Big Bang may finally reveal the distant Oort Cloud, thought to send comets hurtling into the Solar System.
Since the 1930s, astronomers have theorised that a spherical shell of icy objects surrounds the Solar System, 50,000 to 100,000 times further out from the Sun than the Earth.
Oort Cloud
The debris, called the Oort Cloud, is the source of so-called long period comets, which take millions of years to orbit the Sun.
Despite the theory, the cloud has never been spotted from Earth, because although it must be vast, the individual objects are too small and too far away to see.
Now, U.S. astrophysicists Daniel Babich and Avi Loeb from the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts, say we might be able to detect the cloud by studying the Cosmic Background Radiation (CMB). The CMB is leftover radiation from the Big Bang that uniformly pervades space.
Discovering the Oort Cloud would help astronomers understand the early Solar System. Among other things, its shape could narrow down how the outer planets formed and how big they originally were.
The researchers study, published in an upcoming edition of the journal New Astronomy, proposes that massive objects such as passing stars may have redistributed the comets throughout the cloud, causing some to clump together.
Gravity kick
Although the comets are icy (about –268°C), they are still several degrees warmer than the CMB. Therefore the comet's thermal emissions should show up against the background CMB radiation, the researchers said.
"Basically we choose a random star from the observed distribution in the local neighbourhood around the Sun. Then we calculated how the star would influence the Oort Cloud," Babich told Cosmos Online.
The researchers then gauged the effect this star's "kick" would have on the CMB and the hotter Oort Cloud objects and repeated the calculations for 1,000 other stars.
High-resolution maps of the CMB should be able to pinpoint areas of the Oort Cloud 'kicked' by gravity from passing stars. So far, no such map has been made, but all-sky surveys such as that being completed by the European Space Agency's Plank Telescope, set to launch in April 2009, could do the job.
