A team of astronomers has made an important discovery on one of the most distant frozen worlds in our Solar System. The study conducted by the Brazilian Bruno Morgado discovered a ring around Quaoar, a small celestial body located beyond the orbit of Neptune. The discovery was published this Wednesday (8) in Nature magazine and calls attention to the fact that this ring should not exist. At least not according to what we know about the nature of these structures.
How much
Officially called (50000) Quaoar, the object has a diameter of about 1110 km and is considered a dwarf planet, located in the Kuiper belt and orbiting between 41.9 and 45.5 AU from the Sun (1 AU is the mean distance between the Earth and the Sun). Quaoar was discovered in 2002 by American astronomers Chad Trujillo and Michael Brown and because it is located in a region beyond the orbit of the planet Neptune (30 AU from the Sun), it is classified as a trans-Neptunian object, or TNO.
TNOs are practically intact fossils from the formation of the Solar System and their study is essential for understanding how the system formed and evolved up to the present day. That would be enough to draw astronomers’ attention to Quaoar. So much so that, in 2006, it was targeted by the Hubble Space Telescope, and analyzing its images, Michael Brown discovered that Quaoar has a small moon called Weywot, with about 80 km. Now, the team led by Bruno Morgado has discovered that Quaoar also has a ring, all the more reason to take a good look at it. But what makes the Quaoar ring so special?
Rings in small bodies
First, because the presence of rings around small bodies is a recent discovery in the history of astronomy. Until 2013, rings had only been observed around giant planets. It came as a big surprise when an international team, led by Professor Felipe Braga Ribas (PPGFA/UTFPR-Curitiba) discovered the rings around the asteroid (10199) Chariklo. They were the first rings observed around small bodies. In 2017 the same team, composed mainly of Brazilian, French and Spanish researchers, discovered that the dwarf planet (136108) Haumea also has at least one ring.
Thus, Quaoar’s ring is only the third discovered around small bodies in the Solar System. But it has an even more incredible feature: Quaoar’s ring simply shouldn’t be there.
Roche limit and ring formation
Ever since Saturn’s rings were first seen by Galileo Galilei in 1910, their beauty and mystery have intrigued astronomers. It took Dutch observer Christiaan Huygens decades of observation to understand the nature of those rings. And only in the 19th century, the French scientist Édouard Roche developed a hypothesis to explain how Saturn’s rings were formed.
According to Roche, they were formed from fragments of a large icy moon that came very close to the planet and was destroyed by gravitational forces. This theory was based on a mathematical foundation he developed, which makes it possible to calculate a limiting distance at which an object, held together by gravity, can approach another larger object without being destroyed by tidal forces. This distance became known as Roche’s limit, and the theory he developed is considered fundamental to understanding the formation and existence of ring systems.
Roche’s calculations show not only that it would be impossible for a body to remain cohesive when within this limit, but also that it would be equally impossible for a disk of particles to remain in equilibrium outside this limit. The tendency here is for the particles to accumulate and, within a few years, form a moon. But this new discovery contradicts this scenario.
Quaoar’s “impossible” ring
This is because the ring around Quaoar is at a distance of 4,100 km from the asteroid, well beyond its Roche Limit, i.e. it could not have formed from the fragmentation of a body by the action of Quaoar’s tidal forces. And this is something unheard of in astronomy. All other rings observed, both on the giant planets and on small bodies of the Solar System, are located in or near the Roche limit, which means that the hypothesis he developed to explain the origin of the rings also holds. Saturn. apply to these cases, but not to the case of Quaoar.
With that, the discovery triggered original numerical studies presented in the same paper. Numerical simulations were performed using Quaoar ring parameters. The collision laws classically used to describe Saturn’s rings resulted in a rapid accumulation of particles, as expected. However, other collision laws such as those obtained for low temperatures show the opposite. Thus, while the Roche criterion seems valid to explain how a satellite breaks up under tidal forces to form a ring, the reverse process – the accumulation of particles on a satellite – involves more complex mechanisms, which were previously neglected .
Star occultation technique
The discoveries of the rings around Quaoar, Chariklo and Haumea were made using the stellar occultation technique, which consists in measuring the change in brightness of a star when an asteroid passes exactly in front of it. This is a kind of “microeclipse”, which allows you to accurately measure the size and shape of the asteroid, as well as discover the presence of moons and rings around it. Observing stellar occultations requires global collaborations, as the phenomenon is only visible in a narrow band that can cross several locations on Earth.
In the case of Quaoar, the discovery of its ring occurred by detecting small dips in brightness in the light of hidden stars, moments before and after Quaoar itself passed in front of the stars. These dips in brightness occurred in the occultations observed between 2018 and 2021 and together revealed the presence of the ring. By measuring these drops, the physical properties of the ring were determined, such as the width and the amount of material present. In addition to the detection of a much denser structure than the other parts of the ring, something already seen in some rings of giant planets, but never in small bodies.
International cooperation
The discovery of the third ring system around a small body, TNO (50000) Quaoar, was published Feb. 8 in the journal Nature, with lead author Dr. Bruno Eduardo Morgado of Brazil, a professor at the Valongo Observatory. , UFRJ. This study was developed as part of the Lucky Star collaboration, under the leadership of Dr. Bruno Sicardy of the Paris Observatory (Paris, France) and was only possible thanks to the collaboration between dozens of professional and amateur astronomers.
The study saw the participation of researchers from various institutions around the world, such as the Paris Observatory (Meudon, France), the Federal Technological University of Paraná (Curitiba, Brazil), the Astrophysics Institute of Andalusia ( Granada, Spain), the Observatório National (Rio de Janeiro, Brazil), Interinstitutional e-Astronomy Laboratory (Rio de Janeiro, Brazil), University of Oulu (Oulu, Finland) among others. The work also saw the participation of large professional telescopes such as the Gran Telescope of the Canary Islands, robotic telescopes, small telescopes from the amateur community and even the European Space Agency’s (ESA) CHEOPS space telescope.
The discovery should help us understand these structures
New studies are still needed to better understand the Quaoar ring and how it exists outside the Roche limit. However, one thing is clear: This finding shows that rings in small bodies must be more common than previously thought and must come in different shapes, challenging scientists to understand them. Studying these structures can help scientists answer fundamental questions about the mechanisms of moon formation around planets in the Solar System and other star systems.
Source: Olhar Digital