One of the key ways of detecting other worlds is spotting them as they move in front of their star. Photo: Getty
Scientists have spotted a “rogue” planet almost 100 times the size of Earth floating on its own through space.
Most of the planets we know are found orbiting as part of a star system, with one or more suns just like our Earth and the other planets of the solar system.
But some worlds, known as free-floating or rogue planets, drift through the universe independently, seemingly not attached to any star system of their own.
These objects have been much more mysterious, in part because they are far less bright than those other planets.
One of the key ways of detecting other worlds, for instance, is spotting them as they move in front of their star – but, without a star, such rogue planets are much harder to see.
Now scientists have spotted one of those planets using a micro-lensing event, which happens when the gravity from an object magnifies the light from a star behind it.
And because that effect was seen from both ground-based and space-based telescopes, astronomers were able to compare those different positions and use them to work out the mass of the planet.
It is roughly 22pc of that of Jupiter, they say, and the planet is around 3,000 parsecs from the centre of our Milky Way galaxy. The mass of the planet means it probably formed within a planetary system that it has since broken from, the researchers said.
Lower-mass rogue planets of this kind are thought to be thrown into space when there are big gravitational changes in their system, such as interacting with nearby planets or unstable stars.
The newly discovered world is one of only a small number of rogue planets found so far. But the number of them is expected to increase in the years to come, in particular through the launch of Nasa’s Nancy Grace Roman Space Telescope.
The work is described in a new paper, “A free-floating-planet micro-lensing event caused by a Saturn-mass object”, published in the journal Science.