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.
He said: “In the last 15 years we have seen the count of known planets beyond the solar system rising from none to about 700.
“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 researchers could estimate their abundance from the sample obtained. Despite not being able to see the planets, the team noticed their presence by the bending of light rays.
Dr Dominik added: “Probably ever since mankind existed, we have shared our fascination about the myriads of pinpoints of light in the night sky.”