An international research team led by astronomers from the Institute of Astrophysics of Andalusia (IAA-CSIC) in Spain has discovered a ring around Haumea, one of four recognized trans-Neptunian dwarf planets. A paper reporting this discovery is published in the journal Nature.

Beyond the orbit of Neptune lies a frigid, dark, vast frontier of icy bodies left over from the Solar System’s construction 4.6 billion years ago.

This region, called the Kuiper Belt, was hypothesized by astronomer Gerard Kuiper in 1951, but it took another 40 years for astronomers to confirm its existence.

Haumea is the third-largest known dwarf planet in the Kuiper Belt, after Pluto and Eris.

Discovered in 2003 at the Sierra Nevada Observatory in Spain, this dwarf planet is a very elongated and rapidly rotating body. In fact, it is one of the fastest rotating large objects in the Solar System — it completes a turn on its axis every 4 hours.

Haumea has at least two moons, Hi’aka and Namaka. It takes 285 Earth years for the dwarf planet to make one orbit around our Sun.

“Kuiper Belt objects are difficult to study because of their small size, their low brightness, and the enormous distances that separate us from them,” said IAA-CSIC astronomer Dr. José Luis Ortiz.

“A very efficient but complex method lies in the study of stellar occultations, or the passing of these objects in front of a star (like a small eclipse).”

“It allows us to determine the main physical characteristics of an object and has been successfully applied to Pluto, Eris and Makemake.”

“We predicted that Haumea would pass in front of a distant star called URAT1 533-182543 on January 21, 2017, and twelve telescopes from ten different European observatories converged on the phenomenon,” he added.

“This deployment of technical means allowed us to reconstruct with a very high precision the shape and size of Haumea, and discover that it is considerably bigger and less reflecting than was previously believed. It is also much less dense than previously thought, which answered questions that had been pending about the object.”

Dr. Ortiz and co-authors found that Haumea has elliptical projected shape with axes of about 1,059 miles and 707 miles (1,704 km and 1,138 km).

They also found that Haumea’s largest axis is at least 1,443 miles (2,322 km), larger than previously thought, implying an upper limit for its density of 1,885 kg/m3, and found no signs of global nitrogen- or methane-dominated atmosphere.

“One of the most interesting and unexpected findings was the discovery of a ring around Haumea,” said IAA-CSIC astronomer Dr. Pablo Santos-Sanz.

Haumea’s ring has a width of 43.5 miles (70 km), a radius of about 1,421 miles (2,287 km), and is coplanar with both Haumea’s equator and the orbit of its satellite Hi’iaka, according to the researchers.

The radius of the ring places it close to the 3:1 mean-motion resonance with Haumea’s spin period — that is, the dwarf planet rotates three times on its axis in the time that ring particles complete one revolution.

“There are different possible explanations for the formation of the ring; it may have originated in a collision with another object, or in the dispersal of surface material due to the planet’s high rotational speed,” Dr. Ortiz said.

“It is the first time a ring has been discovered around a trans-neptunian object, and it shows that the presence of rings could be much more common than was previously thought, in our Solar System as well as in other planetary systems.”

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J.L. Ortiz et al. 2017. The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation. Nature 550: 219-223; doi: 10.1038/nature24051