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Ring discovered orbiting dwarf planet Haumea

Ringed Haumea of the Outer Solar System

Artist’s rendition of the dwarf planet Haumea with a ring. Image Credit: Instituto de Astrofísica de Andalucía

Scientists were surprised to find a narrow ring circling the dwarf planet Haumea when they observed the small world pass in front of a background star in January 2017.

Jose-Luis Ortiz and Pablo Santos-Sanz of the Institute of Astrophysics of Andalusia in Granada, Spain, along with scientists from more than 50 institutions, took advantage of the unusual event with the purpose of obtaining more accurate information about Haumea’s size, shape, and density.

Numerous telescopes worldwide were aimed at football-shaped Haumea as it occulted a dim red star in the constellation Boötes on January 21, 2017.

Currently located 50.5 AU (4.7 billion miles / 7.6 billion kilometers) from the Sun and 17.1 AU (1.6 billion miles / 2.6 billion kilometers) beyond Pluto, Haumea takes 285.5 years to orbit the Sun. Its orbit is elliptical, and it rotates on its axis every 3.9 hours, the fastest rotation rate of any Solar System object longer than 62 miles (100 kilometers). The rapid rotation may have flattened the dwarf planet into its current oval shape.

Haumea rotation

The dwarf planet Haumea rotates in just under 4 hours. This rapid rotation causes the dwarf planet to be elongated in appearance. Credit: Stephanie Hoover / CC Wikipedia

Just before and after the small world completely covered the star, scientists observed a fading of starlight caused by the 43-mile- (70-kilometer) wide ring around the dwarf planet.

Ortiz, who was a member of one of the two teams that discovered Haumea in 2005, and is the lead author of a study on the findings published in the journal Nature, reported the event was observed by a network of 12 telescopes spread around central Europe. At each telescope, observers measured the light fluctuations caused by the occultation.

The discovery marks the first time a ring has been discovered orbiting a dwarf planet as well as the first time a ring has been found circling a world beyond Neptune.

All four of the Solar System’s gas giants have rings. In 2013 and 2015, rings were discovered around two Solar System objects known as centaurs: 10199 Chariklo and 2060 Chiron, respectively.

Centaurs are asteroid-comet hybrids that have unstable orbits because they reside in the region of the outer Solar System and, therefore, subject to perturbation from the four giant planets’ gravitational influence.

Prior to the New Horizons flyby, mission scientists searched for rings around Pluto, fearful that debris particles in any existing rings could pose a hazard to the spacecraft; however, none were found.

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

Because the star dimmed abruptly rather than gradually when Haumea passed in front of it, scientists determined that the dwarf planet does not have an atmosphere.

The occultation also enabled scientists to constrain Haumea’s size. While its widest point – 1,443 miles / 2,322 kilometers – has a diameter close to that of Pluto (1,479 miles / 2,380 kilometers), its narrowest point is 707 miles (1,138 kilometers), less than half Pluto’s diameter. Haumea’s ring is located about 1,423 miles (2,290 kilometers) from the dwarf planet’s center.

William McKinnon of Washington University in St. Louis, MO, suspects Haumea’s shape, its rapid rotation, its two moons, and its ring all stem from the impact of a large object that hit it, increasing its spin and ejecting materials that formed its moons and rings.

If the impact was powerful enough, it might also have produced other Kuiper Belt Objects that take almost the same paths around the Sun as Haumea and are similarly composed of rock surrounded by water ice, he said.

Pluto’s largest moon, Charon, was also formed by a giant impact, yet Pluto does not have any rings, Ortiz noted. The discovery could indicate that rings are more common around worlds in this solar system and others than previously thought.

“This is a landmark discovery,” said Alan Stern of the Southwest Research Institute (SwRI) in Boulder, Colorado, who is also New Horizons’ principal investigator.

Haumea’s unique features make it an ideal destination for a future probe, he added.

Video courtesy of Jm Madiedo



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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