Sky & Telescope - June 2023 - 9

SOLAR SYSTEM
IN BRIEF
An Unexpected Ring Around Quaoar
THE DISTANT DWARF PLANET
50000 Quaoar appears to have a ring
that spans far beyond where it ought to
be stable.
" That is not where it was supposed
to be, " says Bruno Morgado (Federal
University of Rio de Janeiro, Brazil),
who led a team of 59 astronomers in
reporting the discovery in the February
9th Nature.
Inside the theoretical Roche limit, a
world's tidal forces exceed the gravitational
force holding together any wouldbe
moon, pulling material apart into a
ring instead. Outside that limit, though,
any dust particles or debris ought to
coalesce under their own gravity -
either that, or drift away over time.
The Roche limit has served as a good
rule of thumb in the solar system. Most
rings around planets, and even around
dwarf planets such as 136108 Haumea
and 10199 Chariklo, lie close to or
within the Roche limit.
But the ring around Quaoar breaks
that rule. The material orbits 4,100 kilometers
(2,500 miles) out, far beyond
the world's Roche limit of 1,780 km.
Morgado's team observed stellar
occultations, in which Quaoar passed in
front of a distant star and momentarily
blocked its light. After finding hints of a
ring, the researchers went back through
previous occultation records, including
those obtained by amateur astronomers
Jonathan Bradshaw, Renato Langersek,
and John Broughton, who had detected
the ring in August 2021.
" We saw the ring in nine different
regions from observations taken
between 2018 and 2021, " Morgado
summarizes.
The ring is irregular, spanning just
5 km in some parts and wider than
300 km in others. If its material were
collected into a moon, it would be about
10 km in diameter - less than a tenth
the size of Quaoar's moon, Weywot.
A few thin, lightweight rings exist
beyond the Roche limit elsewhere in the
solar system - like the tenuous rings
beyond Saturn's F ring - but nothing so
massive as the ring around Quaoar.
Amanda Sickafoose (Planetary Science
Institute), who wasn't involved
with the study, notes that the team
hasn't yet demonstrated a full ring
system. Nevertheless, she calls the find
" intriguing, " adding that it " calls into
question our basic understanding of
how ring systems form and evolve. "
¢JEFF HECHT
Amateur Discovers Dwarfs
In 2020, amateur astronomer Giuseppe
Donatiello was poring over images made
public by the Dark Energy Survey (DES),
which had recorded the southern sky from
Chile. Amid the smattering of stars, gas,
and dust, he noticed three new satellites
near the Sculptor Galaxy (NGC 253).
Dwarf-size and spheroidal in shape, they
had been overlooked by the algorithm set
up to spot them. The dwarf galaxies were
dubbed Donatiello II, III and IV. A previous
quest to photograph the satellites of the
Andromeda Galaxy (M31) had already led
Giuseppe to unearth Donatiello I. Including
two others in the Local Group, his
total count is now six. A paper detailing
the newest discoveries was published in
collaboration with David Martínez-Delgado
(Institute of Astrophysics of Andalusia,
Spain) and others in 2021. More recently, a
different team headed up by Burçin MutluPakdil
(University of Chicago), also in
search of satellites of NGC 253, used the
Hubble Space Telescope to obtain images
of a number of them. Among them was
Donatiello II, now independently corroborated.
Hubble, with its precise distance
measurements, was moreover able to
conclusively demonstrate Donatiello II's
association with NGC 253.
¢KIT GILCHRIST
Read more: https://is.gd/Donatiello.
Asteroid Adventure
On February 12th, astronomers detected
pAn artist's impression of the ring around dwarf planet Quaoar. Quaoar's moon Weywot is at left
and the distant Sun at right. (Note that the nine occultations observed showed only pieces of this
ring, which appears to vary greatly in width.)
a 1-meter (3-foot) asteroid roughly 7 hours
before it impacted Earth's atmosphere.
Astronomer Krisztián Sárneczky spotted
the asteroid, now known as 2023 CX1,
as he was working at the GINOP KHK
observatory in Hungary. Observatories in
Croatia and Italy confirmed the detection
and pinned down the orbit, determining
that 2023 CX1 would head for a terminal
point off the northern coast of France.
Observers across Europe tracked the rock
until it flamed harmlessly over the English
Channel. Afterward, the Vigie-Ciel group
of the Fireball Recovery and Interplanetary
Observation Network (FRIPON) scoured
the strewn field in Normandy, France;
18-year-old art student Loïs Leblanc spied
the first fragment in a field near SaintPierre-le-Viger.
The palm-size, 100-gram
(3.5-ounce) stone represents the third
recovery of fragments of an asteroid that
was discovered before impact. Additional
fragments have since been found.
¢DAVID DICKINSON
sk yand tele scope .o r g * JUNE 2023
9
ESA / CC BY-SA 3.0 IGO

https://www.is.gd/Donatiello https://skyandtelescope.org/

Sky & Telescope - June 2023

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