A thin band of debris circles the dwarf planet Haumea in an illustration based on the latest discovery.
ILLUSTRATION BY IAA-CSIC/UHU

While watching a tiny planet eclipse a very distant star, astronomers made an unexpected discovery: The egg-shaped world hosts a 43-mile-wide ring of particles and debris.

That egg, called Haumea, is now the first official dwarf planet found to host a ring system, and only the third body smaller than Neptune known to have rings. The discovery also marks the first time anyone has found rings around an object in the Kuiper belt, a region of icy bodies out beyond the orbit of Neptune.

Ultimately, the revelation may help scientists better understand why and how rings form. But it also gives planners for deep-space missions, like the New Horizons spacecraft that flew past Pluto, an extra item on the checklist of hidden hazards to watch for as the probe hurtles toward its next destination.

The discoverer of six moons and three planetary rings—including the gossamer rings of Jupiter—Mark Showalter is currently heading up the hazard planning team for New Horizon’s next flyby target, a tiny object in the Kuiper belt known as MU69.

“I’m sort of torn. Scientifically, this is fascinating. But as someone with MU69 on his mind, I did meet the news with some trepidation,” says Showalter, a planetary scientist at the SETI Institute.

“We hadn’t not assumed there was a ring, but it drives home the point that there are generally things out there that we might not know about. We’ll be doing a great deal of studying and preparation.”

OBSERVING THE OCCULT
Jose-Luis Ortiz, a solar system researcher with the Instituto de Astrofísica de Andalucía in Spain, has been studying Haumea since he helped discover it in 2005.

In a study published today in the journal Nature, Ortiz describes how a network of 12 telescopes spread across 10 locations in central Europe watched as Haumea passed between Earth and the star URAT1 533-1825 on January 21, 2017.

By taking detailed measurements of the light fluctuations at each location as Haumea passed in front of—or occulted—the star, Ortiz and his team were able to calculate Haumea’s diameter, shape, brightness, and density.

As a bonus, just before and just after Haumea blotted out the star, the telescopes also saw the starlight slightly fade out again: a signature for the presence of a ring.

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SOURCE: National Geographic, Michelle Z. Donahue