Goblin points to Planet Nine

Among some astronomers, there is a growing suspicion that our solar system’s distant reaches conceal a large, ninth planet that we have not yet seen. New findings about a small ice world far beyond Pluto buttress this idea.

Recently, astronomers led by Scott Sheppard of the Carnegie Institution for Science in Washington revealed the orbital details of the world, which they have nicknamed the Goblin. Sheppard and his colleagues first spotted the world, which for now carries the official designation of 2015 TG387 as part of a systematic search three years ago for new worlds in the outer system, including the hypothesized Planet Nine. But only with additional observations did they realize how far out TG387 really is.

“It took us three years to figure out that it has an interesting orbit,” Sheppard said.

The astronomers have submitted a paper describing the discovery to The Astronomical Journal.

The world, estimated to have a width of a couple of hundred miles, is about 7.4 billion miles from the sun, or about 2.5 times farther away than Pluto. But that is near to the closest it ever gets to the sun.

At the other, most distant end of its elliptical, 40,000-year orbit, TG387 is nearly 70 times farther from the sun than Pluto — more than 200 billion miles.

Because TG387 remains far beyond the pull of the gravitational heavyweights of the solar system — Jupiter, Saturn, Uranus and Neptune — that raises the question of how it got thrown into its current orbit.

Astronomers — including Sheppard’s team in 2014 — have discovered several bodies with such distant, stretched-out orbits. The orbits of these objects seem to not be entirely random.

In 2016, Michael Brown and Konstantin Batygin of the California Institute of Technology published a detailed prediction of what they called an unseen planet, bigger than Earth yet smaller than Neptune, that was shepherding the movement of these distant worlds and could explain the odd journeys around the sun of these worlds. They named it Planet Nine. Ann-Marie Madigan, an astronomer at the University of Colorado, has suggested that gravity from a massive ring of small worlds early in the solar system’s history could explain the distant orbits. Madigan’s ideas could help explain how the ice worlds were cast out there, but not any clustering in their orbits.

“This new object does look like it’s quite good for the Planet Nine theory,” she said.

Carnegie Institution for Science This rendering shows a large, unseen ninth planet that some astronomers say must be orbiting the sun at a great distance to explain the orbits of other smaller objects.