Young and hot: This is an artist’s illustration of the giant planet HR 8799b. First discovered in 2007, it was recently found hidden in archival data from the Hubble Space Telescope. It is slightly larger than Jupiter and may be at least seven times more massive.
Credit: NASA, ESA, and G. Bacon (STScI)
BRISBANE: A new image processing technique can be used to scan more than a decade's worth of data from the Hubble Space Telescope to find undiscovered exoplanets, researchers claim.
Exoplanets, which are planets outside our Solar System, are normally difficult to find, because they can be billions of times dimmer than the stars they orbit.
The new technique, which effectively removes the glare surrounding stars in Hubble's images, means that researchers can detect objects that are one-tenth as bright as the previous lower limit, according to a report last week in The Astrophysical Journal.
Adapted for Hubble
"We can achieve a much better detection sensitivity than previously possible with [Hubble]," said lead author David Lafreniere, an astronomer at the University of Toronto in Canada.
The original technique, called the locally optimised combination of images (LOCI) algorithm, was designed for images taken by ground-based telescopes, Lafreniere said, but it was easy to adapt it for use in the Hubble dataset.
The technique works by taking into account the way light from a star is diffracted and scattered as it makes its way through the telescope, which makes the star appear to extend over a larger space than it actually does.
By comparing images of stars that closely resemble each other, the LOCI algorithm determines what portion of an image is actually diffracted or scattered starlight. That light can then be subtracted from the image to reveal dimmer planets that were hidden by their much-brighter star.
Confirmation of discoveries
Lafreniere's team has already demonstrated the technique by finding the exoplanet HR 8799b in an image taken by Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) in 1998, nine years before the planet was first discovered by ground-based telescopes in Hawaii.
As well as making it possible to discover new exoplanets, using the LOCI algorithm on the Hubble dataset will help confirm the status of many putative exoplanets discovered by other telescopes, by providing images over a long timespan, said Lafreniere's co-author Christian Marois, of the Herzberg Institute of Astrophysics in Victoria, Canada.
For example, by comparing images taken over several years, astronomers can confirm that an object really is orbiting a star.
