There's a ring around this dwarf planet which shouldn't be there

A small icy world far beyond Neptune possesses a ring like the ones around Saturn. Perplexingly, the ring is at a distance where simple gravitational calculations suggest there should be none.

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“That’s very strange,” said Professor Bruno Morgado from the Federal University of Rio de Janeiro in Brazil.

He is the lead author of a paper published in the journal Nature in February that describes the ring that encircles Quaoar, a planetary body about 1126km in diameter that orbits the Sun at a distance of about 6.4 billion km.

Quaoar pronounced KWA-wahr, the name of the creator god for the Indigenous Tongva people who live around Los Angeles) is a little less than half the diameter of Pluto and about a third of the diameter of Earth’s moon.

It is likely to be big enough to qualify as a dwarf planet, pulled by its gravity into a sphere. But no one can say that for sure, because images taken by even the most powerful telescopes have revealed Quaoar as only an indistinct blob. The blob also has a moon, Weywot the son of Quaoar in Tongva belief).

Quaoar orbits the Sun in the Kuiper belt, a region of frozen debris beyond Neptune that includes Pluto. The ring is not visible in telescope images. Astronomers found it indirectly, when distant stars happened to pass behind Quaoar and have their light blocked.

From 2018 to 2021, Quaoar passed in front of four stars, and astronomers were able to observe the shadow of the eclipses, also known as stellar occultations.

They also observed some dimming of the starlight before and after the stars blinked out. That pointed to a ring obscuring part of the light, an international team of astronomers concluded in last Wednesday’s Nature paper.