\n<\/p>\n
Are there unseen planets in our solar system?<\/p>\n
Peter Jurik\/Alamy<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
Somewhere at the edge of the solar system a new Earth-sized world might be lurking, dubbed Planet Y.<\/p>\n
Astronomers have long proposed that there might be hidden planets beyond the Kuiper belt, a region of icy objects that is home to Pluto. Some of the more famous suggestions include Planet X, a hypothesised world about seven times the mass of Earth orbiting around 50 times the Earth-sun distance \u2013 now mostly debunked \u2013 and Planet Nine, which would be 10 times the mass of Earth and at least 300 times further from the sun than our planet and which remains a promising possibility.<\/p>\n
<\/p>\n Amir Siraj at Princeton University and his colleagues now propose another world, which they have dubbed Planet Y to make it distinct from the other candidates, based on a warping effect observed on the orbits of some Kuiper belt objects. \u201cIf that warp is real, the simplest explanation is an undiscovered inclined planet,\u201d says Siraj.<\/p>\n The planet, if it exists, would have a mass between that of Mercury and Earth, and orbit at about 100 to 200 times the Earth-sun distance. It would be causing the orbits of some Kuiper belt objects to be slightly inclined out of the flat plane of the solar system, like a ripple in a lake, by about 15 degrees, with the gravity of the planet causing them to move above and below the orbital plane of most other objects.<\/p>\n \u201cOur signal is modest, but credible,\u201d says Siraj, with about a \u201c2 to 4 per cent chance of being a fluke\u201d. \u201cEarly Planet Nine hints quoted similar fluke probabilities.\u201d<\/p>\n The warped plane hinting at Planet Y is distinct from the reasoning behind the possible existence of Planet Nine, with that giant planet thought to be gravitationally tugging objects towards it \u2013 so both could be real. \u201cThe signature is different,\u201d says Siraj.<\/p>\n Jonti Horner at the University of Southern Queensland in Australia says it is \u201cplausible\u201d that there might be unseen worlds such as Planet Y hidden in the outer solar system. \u201cIt plays into the fact that we simply don\u2019t know what\u2019s out there. It\u2019s only in the last couple of decades that we\u2019ve really started to explore the space beyond Neptune,\u201d he says, save for Pluto, which was discovered in 1930.<\/p>\n Worlds such as this would probably have been scattered from the inner solar system into the outer part early on, rather than forming directly out there, where material is sparser. \u201cScattering seems more likely,\u201d says Horner.<\/p>\n Our knowledge of the outer solar system is expected to dramatically shift over the next decade as the Vera C. Rubin Observatory conducts a 10-year survey of the sky. If there is a Planet Y, or a Planet Nine or other candidate planets, Rubin might be able to directly observe them.<\/p>\n \u201cRubin will rapidly expand the catalogue of well-measured trans-Neptunian objects,\u201d says Siraj. If Planet Y does exist, Rubin might detect it \u201cwithin the survey\u2019s first few years\u201d, says Siraj, or at least find further evidence for the warping effect.<\/p>\n Topics:<\/p>\n<\/section><\/div>\n