Tiny, distant planet discovered by Hawaii telescope

A University of Hawaii astronomer is part of a team that discovered the newest minor planet, a relatively small world whose 40,000-year orbit extends to the edges of our solar system.

David Tholen first observed the faint object on Oct. 13, 2015, at the Subaru 8-meter telescope at the summit of Mauna Kea. The discovery was confirmed by subsequent observations from various telescopes over the last three years.

The International Astronomical Union’s Minor Planet Center announced the discovery on Monday, officially dubbing the object 2015 TG387 — although the team gave it a nickname, the Goblin, because the astronomers were working to identify it around Halloween.

It is only the third minor planet having an orbit that never comes close enough to the solar system’s giant planets, like Neptune and Jupiter, to be affected by their gravitational pull.

More important, Tholen said, is the fact that the orbit of 2015 TG387 supports the presence of Planet X, the massive planet hypothesized to be orbiting the sun well beyond Pluto.

Detailed in a paper submitted to The Astronomical Journal, the discovery is credited to Scott Sheppard of the Carnegie Institution for Sciences, Chad Trujillo of Northern Arizona University and Tholen of the UH Institute for Astronomy. Sheppard and Trujillo both earned their doctoral degrees at UH.

The team is on the hunt for Planet X as part of the largest and deepest survey of space ever conducted. The discovery of dwarf planets along the way helps by offering up clues.

“These distant objects are like breadcrumbs leading us to Planet X,” Sheppard said in a news release. “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.”

The team’s software detected the slowly moving object on that October night in 2015, and Tholen measured its position to determine where to point other telescopes for follow-up observations.

“After the first night, we couldn’t say with 100 percent certainty what it was,” Tholen recalled.

But subsequent observation at the Magellan telescope at Carnegie’s Las Campanas Observatory in Chile and the Discovery Channel Telescope in Arizona offered the proof they needed.

The Goblin is a long way from here. The astronomers pegged it at 80 astronomical units (AU) from the sun, which is about 2-1/2 times farther away from the sun than Pluto, which is 34 AU. An AU is the distance between Earth and the sun.

Tholen said not much is known about the tiny world. It has a diameter of roughly 300 kilometers, or about 186 miles across, and is eight times smaller than Pluto.

“We have no physical data on it. We don’t know its color or its composition,” he said. Given its remote and frigid location, it could be covered in ice, he said, but that’s unknown.

The Goblin is traveling slowly across the solar system in an extremely elongated orbit. At its most distant point, the little planet is 2,300 times farther from the sun than Earth. Fortunately, the dwarf is nearing its closest approach to Earth, a distance of 65 AU, he said.

“For some 99 percent of its 40,000-year orbit, it would be too faint to see, even with today’s largest telescopes,” Tholen said.

“We think there could be thousands of small bodies on the fringes of the solar system just like this one,” Tholen added. “This is just the tip of the iceberg.”

Trujillo and University of Oklahoma’s Nathan Kaib ran computer simulations to see how different hypothetical Planet X orbits would affect the orbit of 2015 TG387. Most of the simulations indicated that the gravity of Planet X was having an influence on the minor planet.

“What makes this result really interesting is that Planet X seems to affect 2015 TG387 the same way as all the other extremely distant solar system objects. These simulations do not prove that there is another massive planet in our solar system, but they are further evidence that something big could be out there,” Trujillo said in a news release.