(CNN) Recent telescopic data showed that a small planet in the far reaches of our solar system is surrounded by a dense ring. And scientists are puzzled as to why.
The planet Quaoar is one of about 3,000 small planets orbiting the Sun beyond Neptune and, at 690 miles (1,110 kilometers) wide, is about the seventh largest, with Pluto and Eris being the largest.
Observations of Quaoar conducted between 2018 and 2021 showed that the planet’s ring sits further from it than scientists had previously thought possible, according to a press release from the European Space Agency, using ground-based telescopes and a new space telescope. based telescope called Cheops to collect the data.
Based on conventional thinking, all of the material that makes up Quaoar’s dense ring should have condensed and formed a small moon. But it didn’t.
“Initial results suggest that the cold temperatures at Quaoar may play a role in preventing the ice particles from sticking together, but further investigation is needed,” the press release said.
Beyond the Roche limit
Before these new observations from Quaoar, scientists largely believed that it was impossible for planets to form rings beyond a certain distance. It is a generally accepted rule of celestial mechanics that material in orbit around a planet forms a spherical object – or moon – when it orbits at a sufficient distance from the planet. But that moon will be torn apart if it moves closer than the so-called “Roche limit,” a point where the planet’s tidal forces would be stronger than the gravity that holds the moon together.
All of the rings around Saturn, for example, lie within the planet’s Roche limit. What is puzzling about Quaoar, however, is that its ring lies well beyond the planet’s Roche limit, in a region where the material should form a moon.
“As a result of our observations, the classical notion that dense rings survive only within the Roche limit of a planetary body needs to be thoroughly revised,” said Giovanni Bruno of the Astrophysical Observatory of Catania, Italy, in a statement.
How to study a small planet
According to ESA, collecting the data that revealed the enigmatic ring of Quaoar was cause for celebration in itself. Because of the planet’s small size and distance from Earth, researchers wanted to observe it using an “occultation” — a means of observing a planet by waiting for it to be essentially backlit by a star and its silhouette illuminated.
According to ESA, this can be an extremely difficult process because the telescope, planet and star must be perfectly aligned. This observation was made possible by the space agency’s recent efforts to provide an unprecedentedly detailed map of the stars.
ESA also used Cheops, which was launched in 2019. Cheops typically studies exoplanets, or bodies, that lie outside of Earth’s solar system. But in this case, it has its sights set on the closer target, Quaoar, which orbits even farther from the Sun than Neptune — about 44 times farther than Earth’s orbit.
“I was a little skeptical about the possibility of doing this with CHEOPS,” said Isabella Pagano, the director of INAF’s Catania Astrophysical Observatory, in a statement.
But it worked. And the observation of Cheops was the first-ever of its kind – an occultation by a space-based telescope of one of the most distant planets in our solar system, according to ESA.
The researchers then compared the data collected by Cheops with observations from ground-based telescopes, leading to their surprising revelation.
“Putting it all together, we saw dips in brightness that weren’t caused by Quaoar, but indicated the presence of material in a circular orbit around it. The moment we saw that, we said, ‘Okay, we see a ring around Quaoar,'” said Bruno Morgado, a professor at the Federal University of Rio de Janeiro in Brazil who led the analysis, in a statement.
Theorists – scientists who are experts in various theories – are now trying to guess how Quaoar’s ring survived, according to ESA.