spaceSpace and Physics

Unusually Close Binary Trans-Neptunian Object Spotted By Citizen Scientists


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

TNO binary

An artist's impression of the pair of Trans-Neptunian Objects recently identified when they passed in front of a pair of stars. Southwestern Research Institute

The outer reaches of the Solar System contain many small bodies and hard to study objects. Scientists have teamed with enlisted school groups to learn a little more about one such body and discovered it is actually two, locked together in an unusually tight orbit.

With so many exciting projects clamoring for space agencies' funding, missions following in New Horizon's footsteps, exploring the most distant parts of the Solar System, are likely to be as sparse as space out there. Consequently, one of the few chances we get to learn more about the bodies known as Trans-Neptunian Objects (TNOs) – objects beyond Neptune – is when one passes in front of a star.


Known as an occultation, observing these events can tell us how large the TNO is and sometimes other useful bits of information. However, to observe such events takes perfect placement – from much of the Earth, the TNO will seem to skim past the star's edge, rather than block it out. As with an eclipse, the TNO's shadow will travel across the Earth, so we can learn the most if we can combine observations at different points in its path. 

Dr Rodrigo Leiva and Dr Marc Buie of Southwest Research Institute knew getting time on professional telescopes to watch the TNO (523764) 2014 WC510 block out Gaia ID star 3318035546681086336 across western North America in 2018 would be hard. Instead, he enlisted high school teachers from Yuma, Arizona to Oroville, Washington, and provided them with 28-centimeter (11-inch) diameter telescopes and training. Counterparts ran a similar program in Canada.

"To me this project is citizen science at its best," Buie said in a statement. "They're learning as well as making observations and helping to collect data. If they didn't do this, we wouldn't learn about these objects."

Although 41 stations took part, bad weather, technical problems, and one case of looking in the wrong place meant only six produced useful data. Measurements from these revealed an unusually complex light curve. In the Planetary Science Journal Buie has analyzed the observations and concluded they saw a “double object occulting a double star.” The larger of the pair is 181 ± 16 kilometers across, the smaller 138 ± 32 kilometers, in the likely assumption they are equally reflective.


“Binary stars are not unusual and binary objects are not unusual," Buie said. "But it is unusual that we had a binary TNO occulting a binary star."

What may be rarer still is how close the two components of (523764) 2014 WC510 are to each other. Direct observations of TNOs can't identify binaries unless they are at least 1,000 kilometers (600 miles) apart. This pair appears to be separated by just 350 kilometers (210 miles).

Now, the question is whether close binary TNOs are much more common than we realized, with past observations lacking the sensitivity to detect them, or if these school groups helped find something truly rare.


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