Distant worlds chart a path to Planet Nine - Astronomy Magazine

Last December, a trio of astronomers set the record for the most distant object ever discovered in the solar system. And because the small, remote world is located about three times farther from the Sun than Pluto, the researchers dubbed it Farout. Now, not to be outdone (even by themselves), the same group of boundary pushers have announced the discovery of an even more far-flung object. And since the new find sits a couple billion miles farther out than Farout, the team has fittingly nicknamed it Farfarout.

The discovery of Farfarout, which is about 140 astronomical units from the Sun (where 1 AU equals the distance between Earth and the Sun), is quite impressive by its own right. But Farfarout and its nearer sibling are not just record-breakers, they could be trend-setters. Depending on how their orbits shake out, the two may add to a growing pile of evidence that hints at the existence of an elusive super-Earth lurking in the fringes of our solar system: Planet Nine.

Finding Farfarout

The discovery of Farfarout was initially announced during a talk on February 21 by astronomer Scott Sheppard of the Carnegie Institution for Science, and first reported by Science magazine. During the presentation, Sheppard told the audience he’d spotted Farfarout just the night before while he was waiting out a snowstorm.

“It is a fairly faint object discovered by us in January data from the Subaru telescope,” Sheppard told Astronomy via email. “Based on its distance and brightness, it is likely about [250 miles (400 kilometers)] in size.” This is roughly a quarter the diameter of Ceres, which makes Farfarout a relatively small dwarf planet.

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Sheppard, along with astronomers David Tholen of the University of Hawaii and Chad Trujillo of Northern Arizona University, have been in the news a lot lately for their slew of distant discoveries. This is because they are currently carrying out the most comprehensive survey of solar system objects beyond Pluto to date. According to Sheppard’s presentation, their survey has netted 80 percent of all the solar system objects discovered past 60 AU so far.

But Sheppard and his team are not done yet. They expect their survey to spot many more of these distant and faint trans-Neptunian Objects (TNOs), which are frozen, rocky bodies located past Neptune in a region called the Kuiper Belt.

“We have covered about 25 percent of the sky to date in our survey,” Sheppard says. And though Farfarout is about at the observational limit of their telescopes, the larger the object, the easier it is to spot, “so there are likely a few bigger objects even farther out than Farfarout that we should be able to detect.”

However, Sheppard stresses the discovery of Farfarout is still preliminary. In order to confirm both the object’s extreme distance and its orbital path, they will need to collect more images of it moving through the sky. “We only have observed Farfarout for a 24-hour time base,” he said last week. “I’m currently in Chile at the Magellan telescope right now and we are hoping for good weather over the next several days in order to re-observe this interesting object.”

What are they?

Because Farout and Farfarout are so, well, far out, it's extremely difficult to pin down their orbits — let alone their compositions. But by using powerful ground-based telescopes, the researchers are working to collect enough data to tease out the details. However, this will take some time.

For instance, in October 2018, the team announced the confirmation of another distant object, which, in the spirit of Halloween, they nicknamed The Goblin. Though the 200-mile-wide (320 km) icy rock was seen about 80 AU away, it has a very eccentric orbit, which means it swings out very far from the Sun. “The Goblin’s orbit is very large, it has a semi-major axis of some 1,000 AU,” Sheppard says, “meaning it takes some 35,000 years to go around the Sun once.”

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