One of the most important scientific periodicals, the journal Nature, published, on 2/7, a article signed by scientists of different nationalities led by a Brazilian, reporting the presence of rings in Quaoar, a trans-Neptunian space object, that is, one that is further away than the last planet in the Solar System, Neptune.
The most intriguing thing, however, is not the presence of rings, but the distance they are from the central body. Until then, the rings — formed by cosmic dust and debris originating from the collisions of objects such as asteroids and planets, for example — were seen close to the object, as is the case with Saturn. This is not the case with little Quaoar, with its ring surprisingly farther away, contrary to the theory of ring formation.
According to the Roche Limit, a theory proposed by the French astronomer Édouard Roche, in the 19th century, if the ring passes at a distance greater than 2.5 times the radius of the central body, the material in the ring coalesces, forming a natural satellite. Not so with Quaoar.
“When the satellite is very close to the central body, the force of gravity exerted by the planet is different in all regions of this small satellite and ends up fracturing the object, breaking it. When he is distant, it doesn’t exist. So it wouldn’t break, and these rings would come together through collisions over time and form, coalescing on the satellite as well. This is the theory of the Roche Limit”, explains Altair Ramos Gomes Júnior, a professor at the Institute of Physics at the Federal University of Uberlândia and one of the authors of the article.
As the formation of rings involves the gravitational relationship and collisions, comments Gomes Júnior, the understandings acquired with the study of their formations can be applied to other theories, such as those related to collisions of galaxies, for example. “So, there are several later applications. But, at first, what we are trying to understand is the formation of that ring and, with the evolution of studies, how the formation and dynamic evolution of rings in the Solar System can be applied in other studies”, says the professor. “For example, the process of how particles stick together is the initial step in the planetary formation mechanism.”
Saturn
For a long time, Saturn was known as the only ringed planet in the Solar System. But Jupiter, Uranus and Neptune also have rings around them. Because they are more tenuous and difficult to visualize, the rings of these other three planets were only discovered after 1977, while those of Saturn had been discovered by Galileo Galilei in the 17th century.
As Jupiter, Saturn, Uranus and Neptune are the largest planets in the Solar System (Jupiter, the largest of all, is about 11 times larger than Earth, and Neptune, the smallest of the four, is almost four times larger than our planet) , scientists thought that rings only existed on these giant planets.
Chariklo
In 2013, however, a technique known as star occultation allowed a team, also formed by international collaboration, to discover rings in chariklo, an asteroid object that orbits the Sun and is about 235 km in diameter (the Earth is approximately 12,700 km). It was the first ring detected that wasn’t around a planet.
Discovered in 1997, Chariklo is classified as a centaur because it is between the orbits of Jupiter and Neptune (the order of the planets, starting from the Sun, is as follows: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune ).
More specifically, Chariklo is between the orbits of Saturn and Uranus. The distance from Earth to it is about 16 Astronomical Units, that is, 16 times the distance from Earth to the Sun. As the distance from Earth to the Sun is 149.6 million km, this centaur — the largest ever known — is almost 2.4 billion km away from our planet.
Like mythological centaurs (with a body half man, half horse), centaurs in astronomy are objects of the Solar System with characteristics of asteroids (rocky and composed of metals and minerals) and comets (composed of ice and dust).
occultation of stars
The star occultation technique, used by astronomers and amateur observers across continents, is reminiscent of the game of creating images from the shadows of hands placed against a light source. In the application of the technique in astronomy, the source of light is a star.
With the passage of the space object that one wants to study in front of a certain star, its luminosity is interrupted for a fraction of time and this interruption (the shadow) is registered by observers equipped with terrestrial telescopes or by a telescope in orbit in space. . This interruption of luminosity is then analyzed by means of graphs by the observer.
Since 2013, several observations of Chariklo’s two rings have been made from telescopes positioned in various parts of the Earth. In 2017, astronomers were also able to observe rings on Haumea, considered a dwarf planet and discovered in 2004. It is important to note that the rings of Uranus and Neptune were also discovered using the occultation technique in 1977 and 1984, respectively.
James Webb
At the end of 2022, researchers were able to make observations from the most powerful telescope created by man, the James Webb. The equipment, which has its orbit at a balance point between the Earth and the Sun, was launched into space by NASA – the US agency for aeronautical technology and space exploration – in December 2021.
With the same technique of occulting the stars and with the super telescope, the scientists noticed once again, and without the interference of the atmosphere that surrounds the Earth, the rings in Chariklo.
“The direct observations that we have of this occultation show Chariklo and the star, but we cannot see the ring. But when Chariklo passes in front of the star, we, measuring the brightness of the star, manage to detect a drop in brightness caused by this object passing in front. And when there is a ring, we see relatively quick drops in the star’s flux graph, a drop that is caused by the ring when it passes in front of the star”, explains the professor.
Team work
Altair Gomes Junior, from UFU, is dedicated to Astrometry and participates in research with other Brazilian and foreign scientists. At work, he developed, in partnership with Bruno Morgado, a professor at the Valongo Observatory, at the Federal University of Rio de Janeiro (UFRJ) and who discovered the distant rings in Quaoar, the software that makes the predictions, in addition to carrying out the analyzes of the stellar occultations.
These predictions are predictions of the trajectories of space objects and telescopes, made from information from a catalog of stars and the orbits of asteroids, planets, telescopes, etc. The work is fundamental for predicting the alignment between star, object and telescope and making stellar occultations possible.