In hunt for Planet Nine, astronomers discover something very different

18 Dec 2018

Artist’s concept of Farout. Image: Roberto Molar Candanosa/Carnegie Institution for Science

Following on from their discovery of the ‘Goblin’ planet, astronomers have located what is, so far, the most distant planet in our stellar neighbourhood.

The outer fringes of our tiny sector of the Milky Way are a hotbed of activity for astronomers of late, with more advanced telescopes and processing technology allowing us to discover a whole spectrum of new objects.

Now, the most recent discovery announced by the Minor Planet Center in the US has set a new record as the most distant known object in the solar system, designated 2018 VG18.

The object has been given the nickname of ‘Farout’ by those who discovered it, including Scott S Sheppard of the Carnegie Institution for Science in Washington DC, David Tholen of the University of Hawaii and Chad Trujillo of Northern Arizona University.

The extremely distant object – seen to have a pinkish hue in colour – is approximately 120 astronomical units (AU) away, 120 times the distance between the Earth and the sun. The previous record was set by the object named Eris, around 96AU away. By comparison, Pluto is currently about 34AU in distance, making Farout more than three-and-a-half times more distant than the famous dwarf planet.

The discovery comes just a few months after the announcement of another distant solar system object nicknamed ‘The Goblin’, in what is part of the ongoing search for evidence of a possible ‘Planet Nine’, along with other distant solar system objects.

GIF showing Farout, as a tiny dot, moving against a static starry background.

A GIF of the discovery images of 2018 VG18 ‘Farout’ from the Subaru Telescope on 10 November 2018. Farout moves between the two discovery images while the background stars and galaxies do not move over the one hour between images. Image: Scott S Sheppard, David Tholen

A giant, shepherd planet

The existence of a ninth major planet at the farthest reaches of our solar system was first proposed in 2014 to account for many of the strange orbits we see in other objects. This includes The Goblin, which was discovered at about 80AU and has an orbit consistent with it being influenced by a planet of Earth’s size.

The Goblin and another object nicknamed ‘Biden’ never get close enough to the major planets of our solar system such as Jupiter or Neptune to be influenced by their gravity, meaning that these extremely distant objects can be probes of what is happening in the solar system’s outer reaches.

So far, astronomers don’t know the orbit of Farout, meaning they can’t determine if it shows signs of being shaped by Planet Nine. What they can tell, however, is that its brightness suggests it is about 500km in diameter, likely making it spherical in shape and a dwarf planet.

“[Farout] was found in a similar location on the sky to the other known extreme solar system objects, suggesting it might have the same type of orbit that most of them do,” said Sheppard.

“The orbital similarities shown by many of the known small, distant solar system bodies was [sic] the catalyst for our original assertion that there is a distant, massive planet at several hundred AU shepherding these smaller objects.”

Colm Gorey was a senior journalist with Silicon Republic