() — Recent data from a telescope revealed that a small planet located in the far reaches of our solar system is surrounded by a dense ring, and scientists are baffled.
The planet, called Quaoar, is one of approximately 3,000 small planets that orbit the Sun beyond Neptune. With a width of 1,110 kilometers, it is the seventh largest, with Pluto and Eris being the largest.
Observations of Quaoar made between 2018 and 2021 revealed that the planet has a ring located farther away than scientists thought possible, according to a press release from the European Space Agency (ESA), which used telescopes. ground-based telescopes and a new space telescope called Cheops to collect the data.
Artist’s rendering of Quaoar, the largest object to orbit the Sun since the discovery of Pluto in 1930. Quaoar orbits in a region of space called the Kuiper Belt. Credit: G. Bacon/NASA/Getty Images
According to conventional thinking, all the material that makes up Quaoar’s dense ring should have condensed and formed a small moon. But it was not like that.
“Early results suggest that Quaoar’s frigid temperatures may prevent the icy particles from sticking together, but more research is needed,” according to the news release.
Beyond the Roche limit
Before these new Quaoar observations, 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 orbiting a planet will form a spherical object, or a moon, if it orbits a sufficient distance from the planet. But that moon will tear apart if it gets any closer than what’s called the “Roche limit,” a point at which the planet’s tidal forces would be stronger than the gravity holding the moon together.
All 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 an area where the material should form a moon.
“As a result of our observations, the classical notion that dense rings only survive within the Roche limit of a planetary body needs to be thoroughly revised,” Giovanni Bruno of the INAF Astrophysical Observatory in Catania, Italy, said in a statement.
How to study a dwarf planet
The collection of the data that revealed the enigmatic Quaoar ring was itself a cause for celebration, according to ESA. Because of the planet’s small size and its distance from Earth, the researchers wanted to observe it using an “occultation,” a means of observing a planet waiting for a star to backlight it, illuminating its silhouette.
According to ESA, this is an extremely difficult process, since the telescope, the planet and the star must be in perfect alignment. This observation was made possible by recent efforts by the space agency to provide a star map with an unprecedented level of detail.
ESA also used the Cheops telescope, which was launched in 2019. Cheops often studies exoplanets, or bodies outside Earth’s solar system. But for this case, he set his sights on Quaoar’s closest target, which orbits the sun even farther than Neptune, some 44 times farther than Earth’s orbit.
“I was a little skeptical about the possibility of doing this with Cheops,” declared Isabella Paganodirector of the Catania Astrophysical Observatory of the INAF.
But it worked. According to ESA, the Cheops observation was the first of its kind: an occultation of one of the most distant planets in our solar system by a space telescope.
Next, the researchers compared the data collected by Cheops with observations made by ground-based telescopes, leading to their startling revelation.
“When we put it all together, we saw dips in brightness that weren’t caused by Quaoar, but rather pointed to the presence of material in a circular orbit around it. As soon as we saw it, we said, ‘Okay, we’re looking at a ring around Quaoar. ‘” Bruno Morgado, a professor at the Federal University of Rio de Janeiro, Brazil, who led the analysis, explains in a statement.
According to ESA, theorists are now working to try to find out how Quaoar’s ring could have survived.
