“The Goblin” May Point To Super-Earth Haunting The Fringes Of The Solar System

These discovery photos of “the Goblin” were taken 3 hours apart at the Subaru Telescope on October 13, 2015. The object is the jumping dot just above center.
Scott Sheppard

Just in time for Halloween and in fact named in the spirit of the celebration, American astronomer Scott Sheppard and colleagues have discovered a new, extremely distant object well beyond Pluto they nicknamed “the Goblin.”

More formally known as 2015 TG387, the distant asteroid was discovered about 7.5 billion miles from the sun or 2.5 times farther away than Pluto. That’s deep space and yet the sun still exerts its pull at that incredible distance, keeping the icy object in orbit. And what an orbit it is.

Most of the planets revolve around the sun in nearly circular courses, but the Goblin’s path is stretched out or “elongated.” At its closest point, called perihelion, it never comes closer to the Sun than 6 billion miles. But at furthest point, called aphelion, it’s an incredible 214 billion miles away. If we wanted to beam a radio message to the Goblin at aphelion it would take more than 28 hours to get there!

The orbits of the new extreme dwarf planet, 2015 TG387, and its fellow remote asteroids/comets, 2012 VP113 and Sedna, as compared with the rest of the solar system. 2015 TG387 was given its nickname by the discoverers since it was first seen near Halloween AND as reader Tom Ruen points out “TG”are the initials for “The Goblin.” Its orbit lies between the Kuiper Belt of asteroids beyond Neptune and the remote comet depository, the Oort Cloud. Illustration by Roberto Molar Candanosa and Scott Sheppard, courtesy of Carnegie Institution for Science

Because it’s so far away 2015 TG387 is one of the few known objects that never comes close enough to the giant planets, such as Neptune and Jupiter, to have significant gravitational interactions with them. That makes this remote object a proverbial guinea pig for probing the dingy fringes of the solar system.

“We think there could be thousands of small bodies like 2015 TG387 out on the Solar System’s fringes, but their distance makes finding them very difficult,” Tholen said.   “Currently we would only detect 2015 TG387 when it is near its closest approach to the Sun. For some 99 percent of its 40,000-year orbit, it would be too faint to see.”

The object with the most-distant orbit at perihelion, 2012 VP113, was also discovered by Sheppard and astronomer Chad Trujillo, who announced that find in 2014.  That discovery led Sheppard and Trujillo to notice similarities of the orbits of several extremely distant solar system objects. To account for their motions, the two proposed an unknown planet, sometimes called Planet Nine, several times the size of Earth orbiting the sun hundreds of times further than Pluto.  The location in the sky where 2015 TG387 reaches perihelion is similar to 2012 VP113, Sedna (another remote asteroid) and most other known extremely distant objects beyond Neptune, suggesting that something is pushing them into similar types of orbits.

A comparison of 2015 TG387 with the solar system’s known planets and asteroid belts. One AU is the distance between the Earth and the sun or about 93 million miles. Illustration by Roberto Molar Candanosa and Scott Sheppard, courtesy of Carnegie Institution for Science

“These distant objects are like breadcrumbs leading us to Planet X. The more of them we can find, the better we can understand the outer Solar System and the possible planet that we think is shaping their orbits—a discovery that would redefine our knowledge of the solar system’s evolution,” Sheppard added.

Because the object is so far away and moves so slowly it took the team a few years of observations to determine its orbit. The first observations were made in October 2015 and an orbit calculated just this year. Powerful telescopes were used to find and follow the faint object. With a diameter of about 185 miles (300 km), 2015 TG387 may just quality as a dwarf planet of which there are only five classified to date: Pluto, Ceres, Eris, Makemake and Haumea. To qualify as a dwarf planet, an object must directly orbit a star, be large enough that its self-gravity will crush it into a sphere and yet too small to clear its neighborhood of other asteroids or comets.

Trujillo and University of Oklahoma’s Nathan Kaib also ran computer simulations for how different Planet Nine orbits would affect the orbit of 2015 TG387. Most showed that the gravity of an undiscovered planet could be “shepherding” the Goblin and other extremely distant asteroid or comets, keeping them in stable orbits at a comfortable distance away from the massive object. While the simulations don’t prove existence of Planet Nine, they provide evidence that “something big could be out there,” according to Trujillo.

For more, read the original paper about the discovery here.