Enormous disc might be behind the weird orbits of distant solar system objects

21 Jan 2019

Image: © hallowedland/Stock.adobe.com

A team of researchers has found a simpler and less mysterious answer as to why bodies in the distant solar system have strange orbits.

One of the biggest mysteries of out stellar neighbourhood has been the possibility that a giant planet exists at its farthest reaches, but just hasn’t been spotted yet by astronomers.

Dubbed ‘Planet Nine’ – or ‘Planet X’ by others – clues suggesting the planet’s existence have been popping up somewhat regularly of late, with strange orbits observed in dwarf planets and asteroids being put down to the gravitational pull of this theoretical planet.

However, dashing these hopes, a team of researchers from the University of Cambridge has published a paper in the Astronomical Journal claiming that all of these weird orbits are easily explained – and not the result of a giant, undiscovered planet.

This alternate theory suggests that, rather, they are caused by the combined gravitational force of many small objects orbiting the sun beyond Neptune. This disc would be made up of small icy bodies with a combined mass as much as 10 times that of Earth.

Using a simplified model of our solar system, the team showed that the gravitational forces of this hypothetical disc can account for the strange orbital architecture seen, such as the dwarf planet Farout, now the most distant known planet in the solar system.

‘We’re investigating other possibilities’

Interestingly, this is not the first time a giant disc has been mooted as an alternative to the Planet Nine theory; however, this is the first that is able to explain the significant features of the observed orbits while accounting for the mass and gravity of the other eight planets in our solar system.

In addition to accounting for the strange orbits of these distant objects, the team was able to identify ranges in the disc’s mass, its eccentricity and forced gradual shifts in its orientations.

“When observing other systems, we often study the disc surrounding the host star to infer the properties of any planets in orbit around it,” said the study’s co-author, Antranik Sefilian.

“The problem is, when you’re observing the disc from inside the system, it’s almost impossible to see the whole thing at once. While we don’t have direct observational evidence for the disc, neither do we have it for Planet Nine, which is why we’re investigating other possibilities.”

Colm Gorey was a senior journalist with Silicon Republic