The sky is filled with “hundreds of billions” of unknown planets, according to a study.
The international research involving astronomers at the University of St Andrews suggests only a “tiny” fraction of planets have been discovered.
Six years of data was collected and analysed along with Nasa information from its Kepler mission. Researchers used a network of telescopes across the southern hemisphere, from Tasmania and Western Australia to South Africa and Chile, to observe the skies.
In the study, published in the Nature journal today, researchers found that there are at least half as many planets as there are stars in the sky, despite the fact they cannot be seen.
The team was led by Dr Martin Dominik, a Royal Society university research fellow at St Andrews. "In the last 15 years, we have seen the count of known planets beyond the solar system rising from none to about 700," he said.
“We also know that, so far, we have detected only a tiny fraction of planets out there. We expect hundreds of billions exist in the Milky Way alone.” Dr Dominik said the study was like an opinion survey as it looked at a representative sample rather than taking an entire count.
Only a small number of planets were detected but the researchers said they could estimate their abundance from the sample obtained.
Despite not being able to see the planets, the team were made aware of their presence by the bending of light rays. The process, known as a gravitational microlensing event, indicates to astronomers that planets are circling the star and impacting on light it emits.
Dr Dominik added: “Probably ever since mankind existed, we have shared our fascination about the myriads of pinpoints of light in the night sky - making us wonder whether they hint at other worlds like ours or rather unlike ours.
“The first count of other planets did not start until 1995, with the first detection of a planet orbiting a star other than the Sun, and we could subsequently start pointing telescopes to other stars known to host planets.
“But now we understand that there is more out there," he said.
“We do not know yet where all the planets are, how big or small, dense or fluffy they are, or whether they are home to life or not, but our latest results tell us that while we may not see all the planets, wherever in the sky we look, they are there.”
The work is being followed up by the MiNDSTEp (Microlensing Network for the Detection of Small Terrestrial ExoPlanets) campaign, which is continually searching for new worlds.
PA