By Will Dunham
WASHINGTON, Oct 28 (Reuters) - Scientists using a Chile-based telescope have identified an icy object orbiting beyond Pluto that may join our solar system's small roster of dwarf planets.
Researchers said the candidate, named 2026 ED138, has a diameter estimated at between roughly 370 and 930 miles (600 and 1,500 km) and is orbiting about 46 times farther from the sun than Earth. By way of comparison, Pluto orbits at an average of about 40 times farther from the sun than Earth.
The object
was spotted using the new Vera C. Rubin Observatory, on the summit of the Cerro Pachón mountain in central Chile. The telescope is a joint initiative of the US National Science Foundation and US Department of Energy.
Further observations are needed to confirm that the object is a dwarf planet.
If confirmed, 2026 ED138 would join five other dwarf planets recognized by the International Astronomical Union, the global authority on classifying celestial bodies. Those are Pluto, Eris, Haumea and Makemake, all of which orbit beyond the outermost planet Neptune, and Ceres, located in the main asteroid belt between Mars and Jupiter.
Based on the current data, 2026 ED138 would be among the largest of the dwarf planets.
"For me, what this demonstrates is that many exciting discoveries remain to be made with the Rubin Observatory and other telescopes," said astrophysicist Matt Holman of the Center for Astrophysics, Harvard & Smithsonian, who first spotted 2026 ED138.
Pluto long was considered the solar system's ninth and outermost planet, but was reclassified by the International Astronomical Union as a dwarf planet in 2006 because it did not meet the organization's formal definition of a planet. Pluto and the new dwarf planet candidate reside in a frigid region of the solar system populated by various icy bodies.
There are still questions about the size and composition of 2026 ED138. To be considered a dwarf planet, an object must possess sufficient mass for its own gravity to pull it into a round shape. 2026 ED138 appears to have sufficient mass for that, but more observations are needed.
"The main thing we need to do is to establish the physical size of 2026 ED138," Holman said.
"When we observe with Rubin, we are seeing the sun's light reflected from the object," Holman said. "A smaller, more reflective object would show the same amount of light as a larger, less reflective object. Fortunately, by looking at longer wavelengths, with an observatory like ALMA, we can detect the light emitted by the object itself," which is helpful in measuring an object's size.
ALMA, or the Atacama Large Millimeter/submillimeter Array, is a powerful telescope also based in Chile.
The discovery was announced at a scientific meeting in Spokane, Washington.
(Reporting by Will Dunham; Editing by Daniel Wallis)
