Rogue Planets without Orbits More Numerous than Stars

Albert Einstein predicted that large enough objects had the capability to bend light. He was right and astronomers used this technique called microlensing to make an out-of-this-world discovery. It seems that not all planets orbit neighboring stars.

A international team of scientists has found ten planets that are orphans without stars to orbit, roaming freely in our own galaxy, the Milky Way. Now, astronomers believe that these rogue planets may be more numerous than main-sequence stars like our own Sun.

In the latest issue of the journal Nature, astronomers describe how they used microlensing to determine the number of homeless planets floating around in deep space. First, they identified ten Jupiter-size planets that were too far from any light-giving stars. Then they estimated the total number of such rogue planets, based on detection efficiency, microlensing-event probability and the relative rate of lensing caused by stars or planets. They concluded that there could be as many as 400 billion of these wandering planets, far outnumbering main-sequence stars such as our Sun.

This number stunned the study authors.

Yale University astronomer Debra Fischer says, “This is an amazing result, and if it’s right, the implications for planet formation are profound.”

Her colleague and study co-author Takahiro Sumi, an astrophysicist from Osaka University says, “The existence of free-floating planets has been predicted by planetary formation theory, but nobody knew how many there are.”

Now that microlensing has helped find wandering Jupiters, the team is setting its sights on spotting Saturn and Neptune-sized orphan planets. There may be some Earth-sized, rocky planets out there capable of supporting the ingredients for life.

In the future, NASA’s planned space-based Wide-Field Infrared Survey Telescope (WFIRST), will be able to decipher the rapid light blips associated with smaller mass planets detected using microlensing.

Ohio State University astrophysicist Scott Gaudi says, “Detecting Earth-mass unbound planets? That would be very interesting.”

This discovery is likely to open up a whole new sub-discipline in astronomy, the study of unbound exoplanets.