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| Artist impression of Quaoar's rings. Credit: Paris Observatory |
Scientists have discovered a new ring system around a dwarf planet on the
edge of the solar system. The ring system orbits much further out than is
typical for other ring systems, calling into question current theories of
how ring systems are formed.
The ring system is around a dwarf planet, named Quaoar, which is
approximately half the size of Pluto and orbits the sun beyond Neptune.
The discovery, published in Nature, was made by an international team of
astronomers using HiPERCAM—an extremely sensitive high-speed camera
developed by scientists at the University of Sheffield which is mounted on
the world's largest optical telescope, the 10.4 meter diameter Gran
Telescopio Canarias (GTC) on La Palma.
The rings are too small and faint to see directly in an image. Instead, the
researchers made their discovery by observing an occultation, when the light
from a background star was blocked by Quaoar as it orbits the sun. The event
lasted less than a minute, but was unexpectedly preceded and followed by two
dips in light, indicative of a ring system around Quaoar.
Ring systems are relatively rare in the solar system. In addition to the
well-known rings around the giant planets Saturn, Jupiter, Uranus and
Neptune, only two other minor planets possess rings—Chariklo and Haumea. All
of the previously known ring systems are able to survive because they orbit
close to the parent body, so that tidal forces prevent the ring material
from accreting and forming moons.
What makes the ring system around Quaoar remarkable is that it lies at a
distance of over seven planetary radii—twice as far out as what was
previously thought to be the maximum radius according to the so-called
"Roche limit," which is the outer limit of where ring systems were thought
to be able to survive. For comparison, the main rings around Saturn lie
within three planetary radii. This discovery has therefore forced a rethink
on theories of ring formation.
Professor Vik Dhillon, co-author of the study from the University of
Sheffield's Department of Physics and Astronomy, said, "It was unexpected to
discover this new ring system in our solar system, and it was doubly
unexpected to find the rings so far out from Quaoar, challenging our
previous notions of how such rings form. The use of our high-speed camera—
HiPERCAM—was key to this discovery as the event lasted less than one minute
and the rings are too small and faint to see in a direct image.
"Everyone learns about Saturn's magnificent rings when they're a child, so
hopefully this new finding will provide further insight into how they came
to be."
The study involved 59 academics from all over the world, led by the Federal
University of Rio de Janeiro in Brazil.
Reference:
Bruno Morgado, A dense ring of the trans-Neptunian object Quaoar outside its
Roche limit, Nature (2023).
DOI: 10.1038/s41586-022-05629-6
Tags:
Space & Astrophysics