NASA‘s Kepler Space Telescope has found a mysterious population of ‘free-floating’ or ‘rogue’ planets that aren’t bound to any host star.
Based on a technique called gravitational microlensing, researchers reveal there are four new rogue planets in total, which likely have similar masses to that of Earth.
Gravitational microlensing relies on chance events where from a certain viewpoint, one star passes in front of another star.
The planets may have originally formed around a host star before being ejected by the gravitational tug of other, heavier planets in the system, the experts say.
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The four newly discovered planets that are consistent with planets of similar masses to Earth (stock image)
‘We don’t know exactly how far away they are,’ study author Professor Iain McDonald at the University of Manchester told MailOnline.
‘They are not among the nearest stars, but closer than the centre of our Galaxy. So it’s probably most accurate to say they are several thousand light years away.’
The now retired Kepler telescope spent nearly a decade in space looking for Earth-size planets orbiting other stars, but scientists are still analysing its data.
Kepler launched in 2009 and was decommissioned by NASA in 2018 when it ran out of fuel needed for further science operations.
It was launched specifically by NASA with the aim of identifying planets outside of our own Solar System, known as exoplanets.
For this project, researchers used data obtained in 2016 during the K2 mission phase of NASA’s Kepler Space Telescope – an extension of its original mission.
During its two-month K2 campaign, Kepler monitored a crowded field of millions of stars near the centre of our Galaxy every 30 minutes in order to find rare gravitational microlensing events.
This is an artist impression of the Kepler Space Telescope that was decommissioned by NASA in 2018 after nearly a decade of service
During gravitational microlensing, a viewpoint, a close star and a brighter and more distant star come into close alignment for a few weeks or months.
Gravity from the closer star acts as a lens and magnifies the distant star over the course of the transit.
The study team found 27 short-duration candidate microlensing signals that varied over timescales of between an hour and 10 days.
Many of these had been previously seen in data obtained simultaneously from the ground.
However, the four shortest events are new discoveries that are consistent with planets of similar masses to Earth.
These new events do not show an accompanying longer signal that might be expected from a host star, suggesting that these new events may be free-floating planets.
‘These signals are extremely difficult to find,’ said Professor McDonald.
‘Our observations pointed an elderly, ailing telescope with blurred vision at one the most densely crowded parts of the sky, where there are already thousands of bright stars that vary in brightness, and thousands of asteroids that skim across our field.
Artist’s impression of a free-floating planet. Such planets may perhaps have originally formed around a host star before being ejected by the gravitational tug of other, heavier planets in the system
‘From that cacophony, we try to extract tiny, characteristic brightenings caused by planets, and we only have one chance to see a signal before it’s gone.
‘It’s about as easy as looking for the single blink of a firefly in the middle of a motorway, using only a handheld phone.’
Since its launch in 2009, Kepler spotted thousands of exoplanets outside our solar system, despite experiencing mechanical failures and being blasted by cosmic rays.
In 2013, Kepler’s primary mission was concluded when a second reaction wheel broke, which meant that the space craft couldn’t hold a steady gaze at its original field of view.
But Kepler was given a ‘new lease on life’ by NASA on its K2 mission, which required it to shift its field of view to new portions of the sky about every three months.
NASA initially assumed that K2 would only be able to conduct 10 campaigns with the remaining fuel, but it went on to complete an astonishing 16 campaigns.
Confirming the existence and nature of free-floating planets will be a major focus for NASA’s upcoming Nancy Grace Roman Space Telescope and possibly the ESA’s Euclid mission – both expected to detect microlensing events.
‘Kepler has achieved what it was never designed to do, in providing further tentative evidence for the existence of a population of Earth-mass, free-floating planets,’ said study author Eamonn Kerins at the University of Manchester.
‘Now it passes the baton on to Roman that will be designed to find such signals, signals so elusive that Einstein himself thought that they were unlikely ever to be observed.’
The results have been published today in Monthly Notices of the Royal Astronomical Society.