When we imagine a planet, we think of a planet like ours, orbiting a star. But some have a lonely existence, wandering in interstellar space without a sun. Known as “rogue” or “free-floating” planets, these worlds are often challenging to study. With no known stars and no orbit from which to estimate their size, they have generally flown under the radar until now.
In a new study published In Science On Thursday, scientists showed how they measured the mass of one such rogue planet for the first time — a breakthrough that could enable further study of these strange lonely worlds.
Instead of looking at the planet’s orbit, the research team led by Subo Dong of Peking University analyzed how the planet’s gravity, in a so-called microlensing phenomenon, bent light from a distant star from two different vantage points: Earth and the now-retired Gaia space observatory.
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The technique is similar to our eyes’ depth perception, says Dong: Gaia saw the microlensing phenomenon about two hours later than scientists on Earth. That difference in time allowed researchers to measure the distance to the planet and estimate its mass.
“What’s really cool about this work, and really remarkable, is that it’s the first time that we’ve got a mass for these objects,” says Gavin Coleman, a postdoctoral researcher at Queen Mary University of London. Related Comment Also published in Science But was not included in the study. “This was entirely because the authors had both ground-based observations and Gaia observations from two different locations.”
They found that the planet’s mass was similar to that of Saturn. But the findings also give a hint about its past: “Knowing (its mass) is the starting point,” says Dong. “We can begin to understand, okay, what might be the origin, the history of this planet?”
Dong hopes the study will provide a stepping stone for further research to better understand these mysterious cosmic objects. David Bennett, a senior research scientist at the University of Maryland, College Park and NASA, says the discovery will get a boost later this year with NASA’s Nancy Grace Roman Space Telescope, which is scheduled to launch in September. Able to image the entire sky 1,000 times faster than the Hubble Space Telescope, could help identify Romans hundreds of evil planetsAnd with this work, researchers will also have a way to estimate their mass,
“The doors are open to studying this newly emerging population of planets,” says Dong.
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