SpaceRef (EUA)

Brazilian Scientists Investigate Dwarf Planet's Ring

Publicado em 08 maio 2019

Por Peter Moon  |  Agência FAPESP

Discovered in 2004, Haumea is a dwarf planet located beyond the orbit of Pluto in a region of the solar system called the Kuiper Belt. Pluto was demoted from the category of full-fledged planets in 2006 due to the discovery of Haumea and other dwarf planets.

Haumea was officially recognized as a dwarf planet in 2008. Its ellipsoidal shape resembles that of the ball used in rugby or American football. It has two moons and a ring. Because of its ring, Haumea is a member of a group of objects in the solar system that includes the planets Saturn, Uranus, Neptune and Jupiter, as well as the Chariklo and Chiron asteroids, which orbit between Jupiter and Neptune.

The Haumea ring has never been observed directly. Its existence was inferred in 2017 by an international group of astronomers who took detailed measurements of the fluctuations of light while Haumea hid (passed in front of) a star. In space, an occultation occurs when an object passes in front of another from the perspective of an observer.

"The light from the star was observed from Earth while the star was hidden by Haumea." Her brightness diminished when Haumea passed in front of her, allowing astronomers to obtain information about the shape of Haumea, "said Othon Cape Winter, professor headline in São Paulo. School of Engineering of the State University (FE-UNESP) in Guaratinguetá, Brazil.

"The light of the star also faded when the ring passed in front of her, which allowed them to obtain information about the ring as well."

The researchers who discovered the ring in 2017 suggested that its orbit around Haumea was very close to the 1: 3 resonance region, which means that the ring particles make a revolution every three times that Haumea rotates.

A new study by Winter, Taís Ribeiro and Gabriel Borderes Motta, who belong to the Orbital Dynamics and Planetology Group of the UNESP, shows that a degree of eccentricity would be required for this resonance to act on the particles of the ring. According to Winter, the fact that the ring is narrow and practically circular avoids the action of resonance. However, the group identified a specific type of stable, almost circular, periodic orbit in the same region as the Haumea ring. A periodic orbit is an orbit that repeats itself over time.

"Our study is not observational, we did not observe the ring directly, nobody has ever done it," Winter said. The reason is that the ring is very thin and too far away to be seen by astronomical observatories here on Earth. The average distance between Haumea and the sun is 43 times the distance between Earth and the sun.

"Our study is completely computational." Based on simulations that use the available data on Haumea and the ring, subject to Newton's law of gravitation, which describes the movements of the planets, we conclude that the ring is not in that region of space due to 1: 3 resonance, but due to a family of stable periodic orbits, "said Winter.

In an article published in Monthly notices from the Royal Astronomical Society, researchers explore the dynamics of individual particles in the region where the ring is located.

The research behind the document was part of the Thematic Project "On the relevance of small bodies in orbital dynamics", funded by the São Paulo Research Foundation (FAPESP) and supported by the Brazilian federal government through CAPES, the council of higher education research and the CNPq, the National Council for Scientific and Technological Development.

"The main objective of our research was to identify the structure of the Haumea ring in terms of the location and size of stable regions, we also wanted to find the reason for the existence of the ring, we were particularly interested in trying to understand the structure dynamics associated with its 1: 3 resonance, "said Winter.

Stable regions

The researchers used the Poincaré section surface technique to analyze the dynamics of the region in which the ring is located. By simulating the trajectories of the particles in the region, they generated computer graphics (sections) that showed stable areas represented as islands (closed curves) and unstable areas represented as irregularly distributed points.

The islands of stability that were found due to the 1: 3 resonance had highly eccentric orbits, more than would be compatible with the ring (narrow and circular).

"On the other hand, we detected islands of stability in the same area, but with trajectories of low eccentricity that were compatible with the ring, it was found that these islands were due to a family of periodic orbits," Winter said.

Haumea has a diameter of 1,456 km, less than half the diameter of Mars and an oval shape that makes it twice as long and wide. It takes 284 years to surround the sun. The dwarf planet is so far away, and the sunlight that reaches it is so weak that the temperature of its surface is minus 223 ° C.

The moons of Haumea, Namaka and Hi iaka, were detected by the giant lenses of one of the observatories on the top of the inactive Hawaiian volcano, Mauna Kea. The dwarf planet is named after the Hawaiian goddess of fertility and childbirth, and its moons are named after the daughters of Haumea. It is believed that they have resulted from a collision between the dwarf planet and some other body.

Haumea completes a rotation in less than four hours, spinning faster than any other equilibrium body known in the solar system. This may have to do with a violent past.

Astronomers think that Haumea looked a lot like Pluto when the solar system was formed. Billions of years ago, a large object may have collided with Haumea, ejecting most of its ice surface and spinning it much faster than the other dwarf planets.