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Wandering planets could outnumber the stars in our galaxy

Rogue Planet (Animation)

In the depths of space, in the vast expanses between stellar systems, there float lonely planets which have no star to orbit around. These isolated travelers are called rogue planets, but we really don’t know how many of them are out there. Now, a new study suggests that NASA’s upcoming Nancy Grace Roman Space Telescope could be able to identify hundreds of these rogue planets, which could even outnumber the stars in our galaxy.

“The universe could be teeming with rogue planets and we wouldn’t even know it,” co-author of the study Scott Gaudi, professor of astronomy at Ohio State University, said in a statement. “We would never find out without undertaking a thorough, space-based microlensing survey like Roman is going to do.” Roman will search for rogue planets in particular regions of space and, from this data, scientists can ascertain how many rogue planets might exist.

High-resolution illustration of the Roman spacecraft against a starry background.
High-resolution illustration of the Roman spacecraft against a starry background. NASA's Goddard Space Flight Center

Microlensing is a technique in which astronomers use telescopes like Roman to see distant objects, by looking at the way light is bent when another object passes between us and the target. This allows them to see far-off stars by using these intermediate objects like a magnifying glass.

Rogue planets are typically hard to spot because they are not near to a source of light like a star. But Roman will be able to detect them using microlensing. “This gives us a window into these worlds that we would otherwise not have,” lead author Samson Johnson, a graduate student at Ohio State University said in another statement. “Imagine our little rocky planet just floating freely in space — that’s what this mission will help us find.”

One debate around rogue planets is how they came to be alone — and whether they once did orbit a star. So studying them can help researchers to learn about how planets and stellar systems form.

“As our view of the universe has expanded, we’ve realized that our solar system may be unusual,” Johnson said in the statement. “Roman will help us learn more about how we fit in the cosmic scheme of things by studying rogue planets.”

The findings are published in The Astronomical Journal.

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