Rogue planets that range from Mars mass to Earth mass will be future targets for the Roman telescope. As they cross in front of a star and bend spacetime (therefore bending the star’s light), most may not linger longer than a day, but that’s typically just long enough for observations to be made.
“Gravitational microlensing enables us to study a variety of objects with masses ranging from that of exoplanets to black holes,” the researchers said in the first of two studies soon to be published in The Astronomical Journal. The second study can be found here.
Lonely telescope seeks unattached planets
After it launches in 2027, the Roman telescope will search for rogue planets at the heart of the Milky Way. The research team decided to figure out how many planets we might expect it to find. To do so, they used data from MOA and the Optical Gravitational Lensing Experiment (OGLE) to estimate how many of these planets there are. That approximation was then used to make a prediction of how many could be found in the Milky Way’s central galactic bulge based on the Roman telescope’s capabilities.
“We estimate that our galaxy is home to 20 times more rogue planets than stars—trillions of worlds wandering alone,” said a co-author of both papers, senior research scientist David Bennett of NASA’s Goddard Space Flight Center, in a press release. “This is the first measurement of the number of rogue planets in the galaxy that is sensitive to planets less massive than Earth.”
Bennett and his colleagues also estimated that there are at least six times more small rogue planets than planets with wide orbits in our galaxy’s center, which means their orbits are distant from their star. The masses of these predicted rogues are between Mars’ and Earth’s, based on the cutoffs used by the researchers.
If some planets of this mass have wide orbits and their mass is consistent with many rogue planets, it could mean that at least some rogue planets around the mass of Earth were also once in wide orbits around stars but were thrown into space by intense gravitational interactions with objects in their former exosolar systems. They could have also been ejected during the tumultuous formation of their star systems.
Roman’s instruments should be able to pick up on more microlensing events that reveal these planets than the earlier surveys. It already has high expectations to live up to. For now, at least we have an idea of what might be lurking out there.
Elizabeth Rayne is a creature who writes. Her work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. When not writing, she is either shapeshifting, drawing, or cosplaying as a character nobody has ever heard of. Follow her on Twitter @quothravenrayne.