Dwarf planet Haumea has a ring

Discovery may indicate rings around planets and asteroids are more common than previously thought.
By Laurel Kornfeld | Oct 16, 2017
Dwarf planet Haumea was found to have a narrow, dense ring orbiting it by astronomers who observed the football-shaped world when it occulted, or passed in front of, a background star in January 2017.

The occultation was observed by numerous observatories in various European countries and enabled scientists at the Max Planck Institute for Extraterrestrial Physics and at more than 50 additional institutions to constrain the dwarf planet's shape, size, and density.

When solar system objects such as planets or asteroids pass in front of much more distant stars, scientists can determine the objects' sizes and shapes based on measurements of the projected shadow that is cast on Earth.

"We predicted that Haumea would pass in front of a star on the 21st of January, 2017, and twelve telescopes from ten different European observatories converged on the phenomenon," said study leader Jose Luis Ortiz of the Institute of Astrophysics of Andalusia (IAA-CSIC).

"This deployment of technical means allowed us to reconstruct 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. It is also much less dense than previously thought, which answered questions that had been pending about the object."

Initially estimated to measure 1,400 km at its largest axis, Haumea was revealed to be significantly bigger, with its largest axis measuring 2,320 km.

Haumea has two small moons and takes 284 Earth years to complete a single elliptical orbit around the Sun. It rotates on its axis every 3.9 hours, faster than any other solar system object with a length of more than 100 kilometers.

That rapid rotation is responsible for Haumea's ellipsoid shape, having caused the dwarf planet to flatten out over time.

Because the dimming of the background star during the occultation occurred abruptly rather than gradually, scientists determined Haumea does not have an atmosphere.

No other dwarf planet or trans-Neptunian object is known to have rings. Some scientists thought Pluto might have them, but the New Horizons spacecraft, which flew by the small world in 2015, did not find any.

All four of the solar system's gas giants have rings, as do two small asteroid-comet hybrids known as centuars, in the gas giant region, Chiron and Chariklo.

The discovery suggests rings may be more common than previously believed, both around worlds in our solar system and around those orbiting other stars.

Haumea's ring orbits on its equatorial plane, along with one of the dwarf planet's moons, Hi'iaka.

Ortiz suggested either an impact between Haumea and another object or stirring up of the dwarf planet's surface material by its rapid rotation created the ring.

Findings of the study have been published in the journal Nature.




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