Not all planets are bound to stars. In interstellar space, there is a class of planet-sized objects commonly referred to as rogue planets. We don’t know how many of these rogue planets exist, but a new study published in The Astronomical Journal suggests these celestial bodies might outnumber the stars in the Milky Way.

The research used current knowledge to predict just how powerful the upcoming Nancy Grace Roman Space Telescope will be at detecting rogue planets. The researchers estimate that it will be 10 times more sensitive than existing observatories. If so, it will be able to discover rogue planets as small as Mars all the way up to giant-sized gas objects.

“There have been several rogue planets discovered, but to actually get a complete picture, our best bet is something like Roman. This is a totally new frontier,” lead author Samson Johnson, a graduate researcher at The Ohio State University, said in a statement. “This gives us a window into these worlds that we would otherwise not have. Imagine our little rocky planet just floating freely in space – that’s what this mission will help us find.”

The telescope will use a technique known as gravitational microlensing. Any mass in the universe warps space-time. Extreme objects like black holes do that in a dramatic way. The same goes for massive galaxies and clusters of galaxies, which can create incredible gravitational lenses, magnifying the light of a background galaxy.

Planets can also do that but in a much more minute way. If a rogue planet passes in front of a star from the point of view of the Roman Telescope, it will slightly change its light, which the space observatory will detect.

“The universe could be teeming with rogue planets and we wouldn’t even know it,” added co-author Professor  Scott Gaudi, also at Ohio State. “We would never find out without undertaking a thorough, space-based microlensing survey like Roman is going to do.”

The researchers are confident that based on observations from the Roman Telescope when it's up and running, it will be possible to put a definite upper limit on the number of rogue planets in our galaxy. The observatory is named after Nancy G. Roman, NASA’s first chief astronomer, and it is expected to be launched in the next five years.