During recent observations of the dwarf planet Quaoar, astronomers recorded an unusual event: something almost completely obscured it from view. Researchers are confident that this was neither its moon Weywot nor one of the two known rings of this distant object on the edge of the Solar System.

Features of Quaoar

Quaoar is one of the smallest known dwarf planets, with a diameter of about 1,100 kilometers. It is located approximately 42–45 times farther from the Sun than Earth and lies near Pluto, ranking among the largest trans-Neptunian objects.

Together with the slightly larger Haumea and the much smaller Orcus, Quaoar is a fascinating example of a dwarf planet with its own rings, similar to Saturn. Notably, Quaoar has two rings, both of which are of particular interest to scientists.

Mysterious Rings

Quaoar’s rings are situated at altitudes of about 1,940 and 3,540 kilometers above the planet’s surface. At such distances, Quaoar’s gravity is usually too weak to keep scattered rocks together for long—typically, material at these orbits should coalesce into moons. Why this hasn’t happened remains a mystery for astronomers.

To better understand this phenomenon, scientists recently conducted new observations during moments when Quaoar’s rings pass in front of a star from the perspective of an Earth-based observer. Thanks to their accumulated experience, astronomers knew that the rings are fairly transparent and cannot completely block the starlight—they at most create a faint “misty veil.”

An Unexpected Eclipse

However, just over two minutes before the expected moment, something unexpected occurred: the star was almost entirely obscured for 1.23 seconds, with the degree of dimming reaching 99.9%. Astronomers reported this in a recent publication in Research Notes of the AAS.

The moon Weywot could not have caused this event—its orbit is well known and tracked. The possibility of an airplane, drone, or asteroid passing through the frame was also ruled out. Thus, the cause remains unknown.

Possible Explanations

Astronomers believe the cause may be a dense object. There is a hypothesis that Quaoar may have another, as yet undiscovered, moon. If this is confirmed, the situation would become clearer: perhaps one of the rings is gradually turning into a moon, as is expected to happen at such orbits. Another theory suggests that this is not yet a fully formed moon, but rather a dense clump of material within the ring, which could eventually become a satellite.

It is also possible that this is a third, very massive and dense ring around Quaoar. In any case, such an unusual “wealth” for a miniature world cannot fail to impress researchers.