SPHERE images of Hygiea, Vesta and Ceres
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ESOcast 211 Light: ESO Telescope Reveals What Could be the Smallest Dwarf Planet in the Solar System
Location of Hygiea in the Solar System
Astronomers using ESO’s SPHERE instrument
at the Very Large Telescope (VLT) have revealed that the asteroid Hygiea
could be classified as a dwarf planet. The object is the fourth largest
in the asteroid belt after Ceres, Vesta and Pallas. For the first time,
astronomers have observed Hygiea in sufficiently high resolution to
study its surface and determine its shape and size. They found that
Hygiea is spherical, potentially taking the crown from Ceres as the
smallest dwarf planet in the Solar System.
As an object in the main asteroid belt, Hygiea satisfies right away three of the four requirements to be classified as a dwarf planet:
it orbits around the Sun, it is not a moon and, unlike a planet, it has
not cleared the neighbourhood around its orbit. The final requirement
is that it has enough mass for its own gravity to pull it into a roughly
spherical shape. This is what VLT observations have now revealed about
Hygiea.
“Thanks to the unique capability of the SPHERE instrument on the VLT,
which is one of the most powerful imaging systems in the world, we
could resolve Hygiea’s shape, which turns out to be nearly spherical,” says lead researcher Pierre Vernazza from the Laboratoire d'Astrophysique de Marseille in France. “Thanks to these images, Hygiea may be reclassified as a dwarf planet, so far the smallest in the Solar System.”
The team also used the SPHERE observations to constrain Hygiea’s size, putting its diameter at just over 430 km. Pluto, the most famous of dwarf planets, has a diameter close to 2400 km, while Ceres is close to 950 km in size.Surprisingly, the observations also revealed that Hygiea lacks the very large impact crater that scientists expected to see on its surface, the team report in the study published today in Nature Astronomy. Hygiea is the main member of one of the largest asteroid families, with close to 7000 members that all originated from the same parent body. Astronomers expected the event that led to the formation of this numerous family to have left a large, deep mark on Hygiea.
“This result came as a real surprise as we were expecting the presence of a large impact basin, as is the case on Vesta,” says Vernazza. Although the astronomers observed Hygiea’s surface with a 95% coverage, they could only identify two unambiguous craters. “Neither of these two craters could have been caused by the impact that originated the Hygiea family of asteroids whose volume is comparable to that of a 100 km-sized object. They are too small,” explains study co-author Miroslav Brož of the Astronomical Institute of Charles University in Prague, Czech Republic.
The team also used the SPHERE observations to constrain Hygiea’s size, putting its diameter at just over 430 km. Pluto, the most famous of dwarf planets, has a diameter close to 2400 km, while Ceres is close to 950 km in size.Surprisingly, the observations also revealed that Hygiea lacks the very large impact crater that scientists expected to see on its surface, the team report in the study published today in Nature Astronomy. Hygiea is the main member of one of the largest asteroid families, with close to 7000 members that all originated from the same parent body. Astronomers expected the event that led to the formation of this numerous family to have left a large, deep mark on Hygiea.
“This result came as a real surprise as we were expecting the presence of a large impact basin, as is the case on Vesta,” says Vernazza. Although the astronomers observed Hygiea’s surface with a 95% coverage, they could only identify two unambiguous craters. “Neither of these two craters could have been caused by the impact that originated the Hygiea family of asteroids whose volume is comparable to that of a 100 km-sized object. They are too small,” explains study co-author Miroslav Brož of the Astronomical Institute of Charles University in Prague, Czech Republic.
The team decided to investigate further. Using numerical
simulations, they deduced that Hygiea’s spherical shape and large family
of asteroids are likely the result of a major head-on collision with a
large projectile of diameter between 75 and 150 km. Their simulations
show this violent impact, thought to have occurred about 2 billion years
ago, completely shattered the parent body. Once the left-over pieces reassembled,
they gave Hygiea its round shape and thousands of companion asteroids.
“Such a collision between two large bodies in the asteroid belt is
unique in the last 3–4 billion years,” says Pavel Ševeček, a PhD student
at the Astronomical Institute of Charles University who also
participated in the study.
Studying asteroids in detail has been possible thanks not
only to advances in numerical computation, but also to more powerful
telescopes. “Thanks to the VLT and the new generation
adaptive-optics instrument SPHERE, we are now imaging main belt
asteroids with unprecedented resolution, closing the gap between
Earth-based and interplanetary mission observations,” Vernazza concludes.
More Information
This research was presented in a paper to appear in Nature Astronomy on 28 October.
The team is composed of P. Vernazza (Aix Marseille
Université, CNRS, Laboratoire d'Astrophysique de Marseille, Marseille,
France), L. Jorda (Aix Marseille Université, CNRS, Laboratoire
d'Astrophysique de Marseille, Marseille, France), P. Ševeček (Institute
of Astronomy, Charles University, Prague, Czech Republic), M. Brož
(Institute of Astronomy, Charles University, Prague, Czech Republic), M.
Viikinkoski (Mathematics and Statistics, Tampere University, Tampere,
Finland), J. Hanuš (Institute of Astronomy, Charles University, Prague,
Czech Republic), B. Carry (Université Côte d'Azur, Observatoire de la
Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France), A. Drouard (Aix
Marseille Université, CNRS, Laboratoire d'Astrophysique de Marseille,
Marseille, France), M. Ferrais (Space Sciences, Technologies and
Astrophysics Research Institute, Université de Liège, Liège, Belgium),
M. Marsset (Department of Earth, Atmospheric and Planetary Sciences,
MIT, Cambridge, MA, USA), F. Marchis (Aix Marseille Université, CNRS,
Laboratoire d'Astrophysique de Marseille, Marseille, France, and SETI
Institute, Carl Sagan Center, Mountain View, USA), M. Birlan
(Observatoire de Paris, Paris, France), E. Podlewska-Gaca (Astronomical
Observatory Institute, Faculty of Physics, Adam Mickiewicz University,
Poznań, Poland, and Institute of Physics, University of Szczecin,
Poland), E. Jehin (Space Sciences, Technologies and Astrophysics
Research Institute, Université de Liège, Liège, Belgium), P. Bartczak
(Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz
University, Poznań, Poland), G. Dudzinski (Astronomical Observatory
Institute, Faculty of Physics, Adam Mickiewicz University, Poznań,
Poland), J. Berthier (Observatoire de Paris, Paris, France), J.
Castillo-Rogez (Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, California, USA), F. Cipriani (European Space
Agency, ESTEC – Scientific Support Office, The Netherlands), F. Colas
(Observatoire de Paris, Paris, France), F. DeMeo (Department of Earth,
Atmospheric and Planetary Sciences, MIT, Cambridge, MA, USA), C. Dumas
(TMT Observatory, Pasadena, USA), J. Durech (Institute of Astronomy,
Charles University, Prague, Czech Republic), R. Fetick (Aix Marseille
Université, CNRS, Laboratoire d'Astrophysique de Marseille, Marseille,
France and ONERA, The French Aerospace Lab, Chatillon Cedex, France), T.
Fusco (Aix Marseille Université, CNRS, Laboratoire d'Astrophysique de
Marseille, Marseille, France and and ONERA, The French Aerospace Lab,
Chatillon Cedex, France), J. Grice (Université Côte d'Azur, Observatoire
de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France and Open
University, School of Physical Sciences, The Open University, Milton
Keynes, UK), M. Kaasalainen (Mathematics and Statistics, Tampere
University, Tampere, Finland), A. Kryszczynska (Astronomical Observatory
Institute, Faculty of Physics, Adam Mickiewicz University, Poznań,
Poland), P. Lamy (Aix Marseille Université, CNRS, Laboratoire
d'Astrophysique de Marseille, Marseille, France), H. Le Coroller (Aix
Marseille Université, CNRS, Laboratoire d'Astrophysique de Marseille,
Marseille, France), A. Marciniak (Astronomical Observatory Institute,
Faculty of Physics, Adam Mickiewicz University, Poznań, Poland), T.
Michalowski (Astronomical Observatory Institute, Faculty of Physics,
Adam Mickiewicz University, Poznań, Poland), P. Michel (Université Côte
d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange,
Nice, France), N. Rambaux (Observatoire de Paris, Paris, France), T.
Santana-Ros (Departamento de Fı́sica, Universidad de Alicante, Alicante,
Spain), P. Tanga (Université Côte d'Azur, Observatoire de la Côte
d'Azur, CNRS, Laboratoire Lagrange, Nice, France), F. Vachier
(Observatoire de Paris, Paris, France), A. Vigan (Aix Marseille
Université, CNRS, Laboratoire d'Astrophysique de Marseille, Marseille,
France), O. Witasse (European Space Agency, ESTEC – Scientific Support
Office, The Netherlands), B. Yang (European Southern Observatory,
Santiago, Chile), M. Gillon (Space Sciences, Technologies and
Astrophysics Research Institute, Université de Liège, Liège, Belgium),
Z. Benkhaldoun (Oukaimeden Observatory, High Energy Physics and
Astrophysics Laboratory, Cadi Ayyad University, Marrakech, Morocco), R.
Szakats (Konkoly Observatory, Research Centre for Astronomy and Earth
Sciences, Hungarian Academy of Sciences, Budapest, Hungary), R. Hirsch
(Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz
University, Poznań, Poland), R. Duffard (Instituto de Astrofísica de
Andalucía, Glorieta de la Astronomía S/N, Granada, Spain), A. Chapman
(Buenos Aires, Argentina), J. L. Maestre (Observatorio de Albox,
Almeria, Spain).
ESO is the foremost intergovernmental astronomy organisation in
Europe and the world’s most productive ground-based astronomical
observatory by far. It has 16 Member States: Austria, Belgium, the Czech
Republic, Denmark, France, Finland, Germany, Ireland, Italy, the
Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United
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Strategic Partner. ESO carries out an ambitious programme focused on the
design, construction and operation of powerful ground-based observing
facilities enabling astronomers to make important scientific
discoveries. ESO also plays a leading role in promoting and organising
cooperation in astronomical research. ESO operates three unique
world-class observing sites in Chile: La Silla, Paranal and Chajnantor.
At Paranal, ESO operates the Very Large Telescope and its world-leading
Very Large Telescope Interferometer as well as two survey telescopes,
VISTA working in the infrared and the visible-light VLT Survey
Telescope. Also at Paranal ESO will host and operate the Cherenkov
Telescope Array South, the world’s largest and most sensitive gamma-ray
observatory. ESO is also a major partner in two facilities on
Chajnantor, APEX and ALMA, the largest astronomical project in
existence. And on Cerro Armazones, close to Paranal, ESO is building the
39-metre Extremely Large Telescope, the ELT, which will become “the
world’s biggest eye on the sky”.
Links
- Research paper
- Supplementary material
- New SPHERE view of VESTA
- VLT’s SPHERE spies rocky worlds
- SPHERE maps the surface of Ceres
- Photos of the VLT
Contacts
Pierre Vernazza
Laboratoire d’Astrophysique de Marseille
Marseille, France
Tel: +33 4 91 05 59 11
Email: pierre.vernazza@lam.fr
Miroslav Brož
Charles University
Prague, Czech Republic
Email: mira@sirrah.troja.mff.cuni.cz
Pavel Ševeček
Charles University
Prague, Czech Republic
Email: pavel.sevecek@gmail.com
Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Email: pio@eso.org
Souce: ESO/News
