What Are Trans-Neptunian Objects? Scientists Spot Unusually Close Binary TNOs

With the help of a citizen science research network, a team of researchers has discovered an unusual pair of trans-Neptunian objects (TNO).

Any object in our solar system that has an orbit beyond Neptune is considered a TNO. According to NASA's Jet Propulsion Laboratory (JPL), there are about 70,000 known TNOs, including Pluto, each measuring at least 100 kilometers (62.137 miles​) across.

In a new study, published in The Planetary Science Journal, a team of researchers discovered a TNO pair orbiting each other. The researchers discovered them using a stellar occultation, which occurs when the light of a star is blocked by an object from reaching the observer, a news release from the Southwest Research Institute (SwRI) said.

It is somewhat like a transit, which NASA's TESS uses to search for exoplanets. NASA explains that the difference between the two is that in occultations, the object completely blocks the one behind it whereas, in transits, the object in front only blocks very little of the star behind.

In this case, the data showed that the binary TNO was actually occulting a binary star.

"Binary stars are not unusual and binary objects are not unusual," study co-author Marc Buie of SwRI said in the news release. "But it is unusual that we had a binary TNO occulting a binary star."

The first author of the study, Rodrigo Leiva, also of SwRI, says the two TNOs are orbiting more closely to one another at just 350 kilometers (217.5 miles) away compared to other binary TNOs that have a typical distance of 1,000 kilometers or even more.

Because of the closeness, they were particularly difficult to detect. Scientists were still able to discover them, thanks to the Research and Education Collaborative Occultation Network (RECON) citizen science network of telescopes, which had 56 observation stations in the western U.S. and Canada.

Through the project, high school teachers are trained to use the stations and then they can train students to make observations.

"To me this project is citizen science at its best," Buie said in the news release. "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."

Now, the researchers aim to find is whether binary TNOs that orbit close to each other are unique or if there are many others in the solar system.