by New telescope data has revealed that a dwarf planet in the outer reaches of the solar system has a dense ring around it, leaving scientists and astronomers at a loss as to why.
Scientists at the European Space Agency announced on Wednesday that data and observations of the planet Quaoar collected between 2018 and 2021 – from ground-based telescopes and the Cheops space telescope – led them to the discovery.
The ESA revealed that Quaoar passed in front of a sequence of distant stars and blocked their light as it passed, in an event called an occultation. When the planet blocked that light, scientists were able to see its ring.
Typically, occultations can be difficult to learn from because the alignment of the planet, stars and telescope must be perfect, the ESA explains.
“When we put everything together, we saw drops in brightness that were not caused by Quaoar, but indicated the presence of material in a circular orbit around it,” said Bruno Morgado of the Universidade Federal do Rio de Janeiro in a statement. “The moment we saw that, we said, ‘Okay, we see a ring around Quaoar.'”
Quaoar is part of a collection of about 3,000 dwarf planets known as trans-Neptunian objects, which lie beyond the orbit of the planet Neptune.
Scientists are now wondering why the dense material in Quaoar’s ring hasn’t come together to form a small moon, since the ring itself is “at a distance of nearly seven and a half times the radius of Quaoar,” the scientist said. ESA.
Although rare, Quaoar isn’t the only dwarf planet with a ring. Two others, Chariklo and Haumea, were discovered through ground observations, according to the ESA. However, the placement of Quaoar’s ring makes it more interesting.
Dense ring systems usually exist within what’s known as a planet’s Roche limit, the ESA explained. The Roche limit, which exists around a planet or celestial body, is the point at which a celestial body would be broken into many pieces around it. For example, if Earth’s moon enters the planet’s Roche limit, it would be expected to coalesce into many pieces — perhaps into a ring.
In the case of Quaoar, the dense ring is well beyond the Roche limit, leading scientists to wonder why it exists as a ring rather than a moon.
“As a result of our observations, the classical idea that dense rings survive only within the Roche limit of a planetary body needs to be thoroughly revised,” said Giovanni Bruno of Italy’s National Institute of Astrophysics.
An early guess as to why Quaoar’s dense ring hasn’t formed into a moon is because of the freezing temperatures there, the ESA said. The cold can prevent the ice particles from sticking together.
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