Scientists fear that we could be running out of room in space.
Space may be running out of room
Experts believe that there are four billion space objects currently in the solar system and that many could be UFOs.
The estimate has been provided by Avi Loeb, the former chair of Harvard University's astrology department and the head of the Galileo Project that is searching for evidence of alien technology.
Loeb claims that the majority of objects are small but some are large enough to be manned alien craft. He has called for investment in better telescopes to develop a further understanding of the issue.
The study from Loeb and his fellow Harvard astronomer Carson Ezell suggests that the solar system could be filled with alien objects.
The duo said: "One can use recent rates of detection of interstellar objects and known capabilities to estimate the density of similar objects in the solar neighbourhood."