Artist’s impression close-up of the rings around Chariklo
Artist’s impression of the view from inside the rings around Chariklo
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Chariklo found to have two rings
Observations at many sites in South
America, including ESO’s La Silla Observatory, have made the surprise
discovery that the remote asteroid Chariklo is surrounded by two dense
and narrow rings. This is the smallest object by far found to have rings
and only the fifth body in the Solar System — after the much larger
planets Jupiter, Saturn, Uranus and Neptune — to have this feature. The
origin of these rings remains a mystery, but they may be the result of a
collision that created a disc of debris. The new results are published
online in the journal Nature on 26 March 2014.
The rings of Saturn are one of the most spectacular sights in the
sky, and less prominent rings have also been found around the other
giant planets. Despite many careful searches, no rings had been found
around smaller objects orbiting the Sun in the Solar System. Now
observations of the distant minor planet [1] (10199) Chariklo [2] as it passed in front of a star have shown that this object too is surrounded by two fine rings.
"We weren’t looking for a ring and didn’t think small
bodies like Chariklo had them at all, so the discovery — and the amazing
amount of detail we saw in the system — came as a complete surprise!"
says Felipe Braga-Ribas (Observatório Nacional/MCTI, Rio de Janeiro,
Brazil) who planned the observation campaign and is lead author on the
new paper.
Chariklo is the largest member of a class known as the Centaurs [3]
and it orbits between Saturn and Uranus in the outer Solar System.
Predictions had shown that it would pass in front of the star UCAC4
248-108672 on 3 June 2013, as seen from South America [4]. Astronomers using telescopes at seven different locations, including the 1.54-metre Danish and TRAPPIST telescopes at ESO’s La Silla Observatory in Chile [5], were able to watch the star apparently vanish for a few seconds as its light was blocked by Chariklo — an occultation [6].
But they found much more than they were expecting. A few
seconds before, and again a few seconds after the main occultation there
were two further very short dips in the star’s apparent brightness [7].
Something around Chariklo was blocking the light! By comparing what was
seen from different sites the team could reconstruct not only the shape
and size of the object itself but also the shape, width, orientation
and other properties of the newly discovered rings.
The team found that the ring system consists of two sharply
confined rings only seven and three kilometres wide, separated by a
clear gap of nine kilometres — around a small 250-kilometre diameter
object orbiting beyond Saturn.
"For me, it was quite amazing to realise that we were
able not only to detect a ring system, but also pinpoint that it
consists of two clearly distinct rings," adds Uffe Gråe Jørgensen (Niels Bohr Institute, University of Copenhagen, Denmark), one of the team. "I
try to imagine how it would be to stand on the surface of this icy
object — small enough that a fast sports car could reach escape velocity
and drive off into space — and stare up at a 20-kilometre wide ring
system 1000 times closer than the Moon." [8]
Although many questions remain unanswered, astronomers
think that this sort of ring is likely to be formed from debris left
over after a collision. It must be confined into the two narrow rings by
the presence of small putative satellites.
"So, as well as the rings, it’s likely that Chariklo has at least one small moon still waiting to be discovered," adds Felipe Braga Ribas.
The rings may prove to be a phenomenon that might in turn
later lead to the formation of a small moon. Such a sequence of events,
on a much larger scale, may explain the birth of our own Moon in the
early days of the Solar System, as well as the origin of many other
satellites around planets and asteroids.
The leaders of this project are provisionally calling the
rings by the nicknames Oiapoque and Chuí, two rivers near the northern
and southern extremes of Brazil [9].
Notes
[1] All objects that orbit the Sun,
which are too small (not massive enough) for their own gravity to pull
them into a nearly spherical shape are now defined by the IAU as being small solar system bodies.
This class currently includes most of the Solar System asteroids,
near-Earth objects (NEOs), Mars and Jupiter Trojan asteroids, most
Centaurs, most Trans-Neptunian objects (TNOs), and comets. In informal
usage the words asteroid and minor planet are often used to mean the
same thing.
[2] The IAU Minor Planet Center
is the nerve centre for the detection of small bodies in the Solar
System. The names assigned are in two parts, a number — originally the
order of discovery but now the order in which orbits are well-determined
— and a name.
[3] Centaurs
are small bodies with unstable orbits in the outer Solar System that
cross the orbits of the giant planets. Because their orbits are
frequently perturbed they are expected to only remain in such orbits for
millions of years. Centaurs are distinct from the much more numerous
main belt asteroids between the orbits of Mars and Jupiter and may have
come from the Kuiper Belt region. They got their name because — like the
mythical centaurs
— they share some characteristics of two different things, in this case
comets and asteroids. Chariklo itself seems to be more like an asteroid
and has not been found to display cometary activity.
[4] The event was predicted following a systematic search conducted with the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory and recently published.
[5] Besides the Danish 1.54-metre and
TRAPPIST telescopes at ESO's La Silla Observatory, event observations
were also performed by the following observatories: Universidad Católica
Observatory (UCO) Santa Martina operated by the Pontifícia Universidad
Católica de Chile (PUC); PROMPT telescopes, owned and operated by the
University of North Carolina at Chapel Hill; Pico dos Dias Observatory
from the National Laboratory of Astrophysics (OPD/LNA) - Brazil;
Southern Astrophysical Research (SOAR) telescope; Caisey Harlingten's
20-inch Planewave telescope, which is part of the Searchlight
Observatory Network; R. Sandness's telescope at San Pedro de Atacama
Celestial Explorations; Universidade Estadual de Ponta Grossa
Observatory; Observatorio Astronomico Los Molinos (OALM) — Uruguay;
Observatorio Astronomico, Estacion Astrofisica de Bosque Alegre,
Universidad Nacional de Cordoba, Argentina; Polo Astronômico Casimiro
Montenegro Filho Observatory and Observatorio El Catalejo, Santa Rosa,
La Pampa, Argentina.
[6] This is the only way to pin down the
precise size and shape of such a remote body — Chariklo is only about
250 kilometres in diameter and is more than a billion kilometres from
Earth. Even in the best telescopic views such a small and distant object
just appears as a faint point of light.
[7] The rings of Uranus, and the ring arcs
around Neptune, were found in a similar way during occultations in 1977
and 1984, respectively. ESO telescopes were also involved with the
Neptune ring discovery.
[8] Strictly speaking the car would have to be rather fast — something like a Bugatti Veyron 16.4 or McLaren F1 — as the escape velocity is around 350 km/hour!
[9] These names are only for informal use, the official names will be allocated later by the IAU, following pre-established rules.
More information
This research was presented in a paper entitled “A ring
system detected around the Centaur (10199) Chariklo”, by F. Braga-Ribas
et al., to appear online in the journal Nature on 26 March 2014.
The team is composed of F. Braga-Ribas (Observatório
Nacional/MCTI, Rio de Janeiro, Brazil), B. Sicardy (LESIA, Observatoire
de Paris, Paris, France [LESIA]), J. L. Ortiz (Instituto de Astrofísica
de Andalucía, Granada, Spain), C. Snodgrass (Max Planck Institute for
Solar System Research, Katlenburg-Lindau, Germany), F. Roques (LESIA),
R. Vieira- Martins (Observatório Nacional/MCTI, Rio de Janeiro, Brazil;
Observatório do Valongo, Rio de Janeiro, Brazil; Observatoire de Paris,
France), J. I. B. Camargo (Observatório Nacional/MCTI, Rio de Janeiro,
Brazil), M. Assafin (Observatório do Valongo/UFRJ, Rio de Janeiro,
Brazil), R. Duffard (Instituto de Astrofísica de Andalucía, Granada,
Spain), E. Jehin (Institut d’Astrophysique de l’Université de Liege,
Liege, Belgium), J. Pollock (Appalachian State University, Boone, North
Carolina, USA), R. Leiva (Pontificia Universidad Católica de Chile,
Santiago, Chile), M. Emilio (Universidade Estadual de Ponta Grossa,
Ponta Grossa, Brazil), D. I. Machado (Polo Astronomico Casimiro
Montenegro Filho/FPTI-BR, Foz do Iguaçu, Brazil; Universidade Estadual
do Oeste do Paraná (Unioeste), Foz do Iguaçu, Brazil), C. Colazo
(Ministerio de Educación de la Provincia de Córdoba, Córdoba, Argentina;
Observatorio Astronómico, Universidad Nacional de Córdoba, Córdoba,
Argentina), E. Lellouch (LESIA), J. Skottfelt (Niels Bohr Institute,
University of Copenhagen, Copenhagen, Denmark; Centre for Star and
Planet Formation, Geological Museum, Copenhagen, Denmark), M. Gillon
(Institut d’Astrophysique de l’Université de Liege, Liege, Belgium), N.
Ligier (LESIA), L. Maquet (LESIA), G. Benedetti-Rossi (Observatório
Nacional/MCTI, Rio de Janeiro, Brazil), A. Ramos Gomes Jr (Observatório
do Valongo, Rio de Janeiro, Brazil, P. Kervella (LESIA), H. Monteiro
(Instituto de Física e Química, Itajubá, Brazil), R. Sfair (UNESP -–
Univ Estadual Paulista, Guaratinguetá, Brazil), M. El Moutamid (LESIA;
Observatoire de Paris, Paris, France), G. Tancredi (Observatorio
Astronomico Los Molinos, DICYT, MEC, Montevideo, Uruguay; Dpto.
Astronomia, Facultad Ciencias, Uruguay), J. Spagnotto (Observatorio El
Catalejo, Santa Rosa, La Pampa, Argentina), A. Maury (San Pedro de
Atacama Celestial Explorations, San Pedro de Atacama, Chile), N. Morales
(Instituto de Astrofísica de Andalucía, Granada, Spain), R. Gil-Hutton
(Complejo Astronomico El Leoncito (CASLEO) and San Juan National
University, San Juan, Argentina), S. Roland (Observatorio Astronomico
Los Molinos, DICYT, MEC, Montevideo, Uruguay), A. Ceretta (Dpto.
Astronomia, Facultad Ciencias, Uruguay; Observatorio del IPA, Ensenanza
Secundaria, Uruguay), S.-h. Gu (National Astronomical
Observatories/Yunnan Observatory; Key Laboratory for the Structure and
Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming,
China), X.-b. Wang (National Astronomical Observatories/Yunnan
Observatory; Key Laboratory for the Structure and Evolution of Celestial
Objects, Chinese Academy of Sciences, Kunming, China), K. Harpsøe
(Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark;
Centre for Star and Planet Formation, Geological Museum, Copenhagen,
Denmark), M. Rabus (Pontificia Universidad Católica de Chile, Santiago,
Chile; Max Planck Institute for Astronomy, Heidelberg, Germany), J.
Manfroid (Institut d’Astrophysique de l’Université de Liege, Liege,
Belgium), C. Opitom (Institut d’Astrophysique de l’Université de Liege,
Liege, Belgium), L. Vanzi (Pontificia Universidad Católica de Chile,
Santiago, Chile), L. Mehret (Universidade Estadual de Ponta Grossa,
Ponta Grossa, Brazil), L. Lorenzini (Polo Astronomico Casimiro
Montenegro Filho/FPTI-BR, Foz do Iguaçu, Brazil), E. M. Schneiter
(Observatorio Astronómico, Universidad Nacional de Córdoba, Córdoba,
Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas
(CONICET), Argentina; Instituto de Astronomía Teórica y Experimental
IATE–CONICET, Córdoba, Argentina; Universidad Nacional de Córdoba,
Córdoba, Argentina), R. Melia (Observatorio Astronómico, Universidad
Nacional de Córdoba, Córdoba, Argentina), J. Lecacheux (LESIA), F. Colas
(Observatoire de Paris, Paris, France), F. Vachier (Observatoire de
Paris, Paris, France), T. Widemann (LESIA), L. Almenares (Observatorio
Astronomico Los Molinos, DICYT, MEC, Montevideo, Uruguay; Dpto.
Astronomia, Facultad Ciencias, Uruguay), R. G. Sandness (San Pedro de
Atacama Celestial Explorations, San Pedro de Atacama, Chile), F. Char
(Universidad de Antofagasta, Antofagasta, Chile), V. Perez (Observatorio
Astronomico Los Molinos, DICYT, MEC, Montevideo, Uruguay; Dpto.
Astronomia, Facultad Ciencias, Uruguay), P. Lemos (Dpto. Astronomia,
Facultad Ciencias, Uruguay), N. Martinez (Observatorio Astronomico Los
Molinos, DICYT, MEC, Montevideo, Uruguay; Dpto. Astronomia, Facultad
Ciencias, Uruguay), U. G. Jørgensen (Niels Bohr Institute, University of
Copenhagen, Copenhagen, Denmark; Centre for Star and Planet Formation,
Geological Museum, Copenhagen, Denmark), M. Dominik (University of St
Andrews, St Andrews, United Kingdom) F. Roig (Observatório
Nacional/MCTI, Rio de Janeiro, Brazil), D. E. Reichart (University of
North Carolina – Chapel Hill, North Carolina [UNC]), A. P. LaCluyze
(UNC), J. B. Haislip (UNC), K. M. Ivarsen (UNC), J. P. Moore (UNC), N.
R. Frank (UNC) and D. G. Lambas (Observatorio Astronómico, Universidad
Nacional de Córdoba, Córdoba, Argentina; Instituto de Astronomía Teórica
y Experimental IATE–CONICET, Córdoba, Argentina).
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Email: ribas@on.br
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LESIA, Observatoire de Paris, CNRS
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