Twist in search for mysterious 'Planet Nine' in the dark depths of our solar system

Metro

30-05-2025

Scientists hunting for Planet Nine, an elusive planetary body that could change our understanding of the solar system, have found something.
Planet X is a hypothetical planet seven times the mass of Earth tucked just behind Pluto.
Despite possibly being the fifth most massive planet, scientists have never tracked the white whale of astronomy down – that is, if it even exists.
But a trio of American scientists trying to find the elusive gas giant have discovered a new planet… of sorts, a dwarf planet called 2017 OF201.
According to a study, which has not been peer-reviewed, 2017 OF201 is roughly 430 miles across, three times smaller than Pluto.
The object is an extreme trans-Neptunian object (eTNO), a minor planet that orbits the Sun far beyond Neptune.
So far away, in fact, OF201 would take 25,000 Earth years to complete a solar lap. Its orbit even swings out into the Oort Cloud – a sphere of icy comets a trillion miles from the Sun.
OF201 can only be observed from Earth 0.5% of the time, making its closest approach to us in 1930 and won't do so again until 26,186.
The International Astronomical Union's Minor Planet Center added 2017 OF201 to its database last week. Five other dwarf planets are officially recognised: Pluto, Eris, Ceres and two others beyond Neptune, Haumea and Makemake.
The search for a ninth planet in our solar system has been going on for a century.
The evidence for it that hunters have long clung to is how six objects – dwarf planets and chunks of ice – have been discovered in the vastly empty outskirts of the solar system.
Bizarrely, they huddle together as they orbit, as if something a gassy behemoth of a planet were shepherding them, said Imo Bell, astronomer at the Royal Observatory Greenwich.
They told Metro: 'Some astronomers believe that proving the existence of this planet would explain the behaviour of many other eTNOs with highly elliptical orbits clustered on one side of the Sun.
'It's thought that Planet Nine, with a mass of about five Earths, would explain the confined orbits of these eTNOs.'
Sihao Cheng of New Jersey's Institute for Advanced Study and Princeton University graduate students, Jiaxuan Li and Eritas Yang, discovered 2017 OF201.
They did so by combing through an archive of images of the outskirts of the solar system, taken by the Blanco telescope in Chile, as well as by the Canada-France-Hawaii Telescope in Hawaii.
Over time, they realised that tiny dots in the images were a single dwarf planet-sized rock with a wide and eccentric orbit.
Yang said: 'It must have experienced close encounters with a giant planet, causing it to be ejected to a wide orbit.'
Yet the discovery isn't exactly what the team had hoped for, explained Bell, as it's not part of the pack of eTNOs that imply Planet Nine exists.
They said: 'The discovery of 2017 OF201 is significant because it's found in a region of the Solar System thought to be empty, and it's presence points to the existence of other similar eTNOs with orbits that challenge ideas about Planet Nine as they are not clustered in the way that has been seen with other eTNOs.'
Yang's simulations only considered one proposed orbit of Planet Nine, meaning that the findings don't disprove the planet's existence altogether.
Cheng hasn't lost hope, saying that the existence of 2017 OF201 suggests there 'could be another hundred or so other objects with similar orbit and size'.
'They are just too far away to be detectable now,' he added.
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