Astrophysicists from Harvard University have found what they believe is a previously undiscovered dwarf planet in our own solar system.
The object, which the scientists say is probably between 600 and 1,500 kilometers in diameter, is one of the brightest objects discovered in the solar system in decades.
"We don't really know its size because all we can see is how much light we're getting from it," explained Matthew Holman, a Smithsonian Astrophysicist and lecturer at Harvard University. "So it could either be a very reflective object that's smaller or a very dark object that's bigger."
Regardless, the dwarf planet candidate, which is called 2026 ED138 for now, is still among the seven largest objects identified in the outer solar system so far, the scientists say.
The discovery was announced Tuesday at the 59th Annual Division for Planetary Sciences meeting being held by the American Astronomical Society this week in Spokane, Washington.
The "dwarf planet" designation was adopted in the early 2000s when several new objects as large as Pluto were identified, leaving Pluto demoted to the new category. Dwarf planets orbit the sun and are, by definition, smaller than other planets. But they're still massive enough that their own self-gravity makes them spherical.
The scientists say the object they discovered hadn't previously been found because it's hiding within one of the brightest parts of the night sky — the Milky Way galaxy. So despite the brightness of the object, its location made it difficult to detect.
"This is an object that's actually bright enough that really capable amateurs can see it," Holman said. "So it sort of demonstrates that we have not found all of the treasures in our solar system yet."
The Harvard astrophysicists discovered the dwarf planet candidate with the help of an incredibly powerful telescope at the Vera C. Rubin Observatory.
"This has an eight-meter mirror, which is one of the largest in the world, and that allows the Rubin telescope to collect a lot of light in a relatively short amount of time, allowing us to see ... quite faint objects," Holman said. "The other thing that really makes the Vera C. Rubin Observatory unique is it has an enormous field of view."
Every three nights, the enormous telescope can observe the entire visible sky from its location in Chile.
"Essentially what we do is just play connect the dots with the things that we think could be moving," said astrophysicist Kevin Napier of the Center For Astrophysics at Harvard University and the Smithsonian. "And once you have finally connected enough dots, you can get an estimate for what the orbit of your object is going around the Sun."
The Vera C. Rubin Observatory will be featured in NOVA's upcoming long-form documentary "Universe in Motion," premiering Dec. 16.
The new dwarf planet candidate joins thousands of known objects in an area of the solar system beyond Neptune known as the Kuiper Belt. And the scientists say there may be more of them.
"There have been objects that have been hidden in the haystack or the 'Where's Waldo' game of the galactic center now for the few decades that we've actually known about the Kuiper Belt," said Napier. "And now we can look and actually find them. So who knows what else will turn up?"
Most of the dwarf planets that have been discovered have been at the point in their orbits that is closest to Earth.
"But many of them also make their way [far] out into the distant solar system… three times the distance of Neptune, or even further," Napier said. "So those things would be much fainter because they're much farther away. So the deeper that we can push into the night sky, the more interesting things we may be able to turn up."
Additional telescope imaging is needed to confirm the size of the newly discovered object, Holman said.
"Once we really know its size, then we can make a much more clear statement about whether this is a dwarf planet or not," he said.
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