Two astronomers have published evidence that our solar system contains a ninth planet. Nicknamed Planet Nine, it orbits the Sun far beyond the dwarf world Pluto, which was recently stripped of its planetary status.
According to their paper, published in the Astronomical Journal, the icy world is believed to be up to four times as large and ten times as massive as Earth – almost the size of Neptune.
The Week
Escape your echo chamber. Get the facts behind the news, plus analysis from multiple perspectives.
Sign up for The Week's Free Newsletters
From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.
From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.
"We saw a strange signal in the data that meant something odd was going on in the outer solar system," Mike Brown told The Guardian. "All of these distant objects were lined up in a weird way and that shouldn't happen. We worked through the mundane explanations, but none of them worked out."
What caught their attention was a "peculiar clustering of six previously known objects that orbit beyond Neptune", says Science Magazine. The astronomers say that there is a "0.007 per cent chance, or about one in 15,000, that the clustering could be a coincidence", claiming the more likely explanation is that "a planet with the mass of ten Earths has shepherded the six objects into their strange elliptical orbits, tilted out of the plane of the solar system."
Batygin and Brown hope that by publishing their theory they will encourage other teams to look for the planet. "There are many telescopes on the Earth that actually have a chance of being able to find it," Brown said.
Their calculations suggest that it orbits the Sun once every 10,000 to 20,000 years, at a distance of up to 100 billion miles.
The paper has been peer-reviewed by Alessandro Morbidelli, a planetary dynamicist at the Nice Observatory in France, who said in a statement that the pair made a "very solid argument" and that he is "quite convinced by the existence of a distant planet".
-
Quiz of The Week: 10 – 16 JanuaryQuiz Have you been paying attention to The Week’s news?
-
Woman in Mind: a ‘triumphant’ revival of Alan Ayckbourn’s dark comedyThe Week Recommends Sheridan Smith and Romesh Ranganathan dazzle in ‘bitterly funny farce’
-
The Week Unwrapped: Will Uganda’s pop-star politician prevail?Podcast Plus, is dodgy data undermining medical research? And what does a new app reveal about Chinese society?
-
The ‘eclipse of the century’ is coming in 2027Under the radar It will last for over 6 minutes
-
NASA discovered ‘resilient’ microbes in its cleanroomsUnder the radar The bacteria could contaminate space
-
Artemis II: back to the MoonThe Explainer Four astronauts will soon be blasting off into deep space – the first to do so in half a century
-
The mysterious origin of a lemon-shaped exoplanetUnder the radar It may be made from a former star
-
The 5 biggest astronomy stories of 2025In the spotlight From moons, to comets, to pop stars in orbit
-
Blue Origin launches Mars probes in NASA debutSpeed Read The New Glenn rocket is carrying small twin spacecraft toward Mars as part of NASA’s Escapade mission
-
‘The Big Crunch’: why science is divided over the future of the universeThe Explainer New study upends the prevailing theory about dark matter and says it is weakening
-
The moon is rustingUnder the radar The Earth is likely to blame
