Astronomers Discover A Rogue Planet With Saturn-Like Mass

Astronomers have detected a rogue planet with a mass similar to that of Saturn. Using observations from both ground-based telescopes and space instruments, they were able to measure the planet's size and distance from Earth.

What Are Rogue Planets

Most planets orbit one or more stars, but some planets, known as free-floating or rogue planets, do not have any stellar companion. These planets are usually detected through subtle gravitational effects on background light, a method called microlensing, because they emit very little light themselves.

Microlensing alone often fails to accurately measure the distance or mass of these planets, as this effect is typically observed from only one location.

A team of astronomers led by Subho Dong of Peking University and the National Astronomical Observatories of the Chinese Academy of Sciences discovered a free-flying (rogue) planet during a brief microlensing event. The event was observed from different points both on Earth and in space.

The team analysed data from the Gaia Space Telescope, located 930,000 miles away, along with data from multiple ground-based surveys. By comparing the small differences in the time taken for light to reach each observation point, they determined the planet's mass and its distance from Earth.

Size and Location

Researchers estimate that this rogue planet is approximately 22 percent the mass of Jupiter and is located approximately 3,000 parsecs from the center of the Milky Way.

Since the planet's mass is similar to that of Saturn, the team believes it likely formed within a solar system, rather than around a small star. Low-mass free-flying planets are believed to form first around stars and are later ejected from the solar system due to gravitational instabilities, such as the impact of neighboring planets or an unstable star's companion.