A small planet in the outer reaches of our solar system has a dense ring surrounding it, according to recent telescope data. And the reason is a mystery to scientists.
With a width of 690 miles (1,110 kilometres), the planet Quaoar is about the seventh largest among the about 3,000 tiny planets that circle the sun beyond Neptune. Pluto and Eris are the two largest.
According to a press release from the European Space Agency, observations of Quaoar between 2018 and 2021 revealed that the planet has a ring sitting farther away from it than scientists previously believed was possible. The observations were made using ground-based telescopes and a new space-based telescope called Cheops.
According to traditional wisdom, the entirety of Quaoar’s thick ring should have condensed into a small moon. It didn’t, though.
The news release states that additional research is required because “early data suggest that the cold temperatures at Quaoar may play a role in keeping the icy particles from staying together.”
the Roche limit and beyond
Before these recent discoveries on Quaoar, the majority of scientists thought that planets couldn’t generate rings beyond a specific range. According to a well established principle of celestial mechanics, matter in orbit around a planet will eventually coalesce into a spherical object, or moon, if it orbits at a sufficient distance from the planet. The “Roche limit,” a distance beyond which the planet’s gravitational pull would be greater than the force holding the moon together, will cause that moon to shatter.
For instance, all of Saturn’s rings are contained inside the Roche limit of the planet. However, Quaoar’s ring is far outside the planet’s Roche limit, at a region where the material should form a moon. This is intriguing.
Giovanni Bruno of the INAF’s Astrophysical Observatory in Catania, Italy, said in a statement that “as a result of our discoveries, the classical assumption that dense rings exist only inside the Roche limit of a planetary body must be fundamentally updated.”
How to research a tiny planet
According to ESA, gathering the information that showed Quaoar’s mysterious ring was reason enough to celebrate in and of itself. Researchers planned to view the planet using a “occultation,” which is a technique for observing a planet by waiting for it to be effectively backlit by a star, illuminating its outline. This was done because of the planet’s small size and distance from Earth.
According to ESA, that technique can be very challenging because the telescope, planet, and star must all be perfectly aligned. The space agency’s latest attempts to present an incredibly detailed map of the stars have enabled this finding.
Cheops, which was launched in 2019, was also employed by ESA. Cheops frequently researches exoplanets, or worlds outside the solar system. But in this case, it focused on Quaoar, a closer target that orbits the sun even farther than Neptune — almost 44 times beyond than the orbit of Earth.
Director of the INAF’s Astrophysical Observatory of Catania Isabella Pagano stated, “I was a little doubtful about the feasibility to do this using CHEOPS.
But it did. According to the ESA, Cheops’ observation was the first of its kind: an occulation of one of our solar system’s furthest planets by a space-based telescope.
The unexpected finding was made by researchers after they contrasted the information gathered by Cheops with observations made by telescopes located on Earth.
“When we combined all of the information, we noticed brightness drops that weren’t due to Quaoar but indicated the presence of material in a circular orbit around it. The instant we noticed that, we thought, “Okay, we are seeing a ring around Quaoar,” said Bruno Morgado, the analysis’s principal investigator and a professor at Brazil’s Federal University of Rio de Janeiro.