Ceres is the largest body in the asteroid belt between Mars and Jupiter and the only such object classed as a dwarf planet. NASA's Dawn spacecraft has been in orbit around Ceres for more than a year and has mapped its surface in great detail. One of the biggest surprises has been the discovery of very bright spots, which reflect far more light than their much darker surroundings . The most prominent of these spots lie inside the crater Occator and suggest that Ceres may be a much more active world than most of its asteroid neighbours.
New and very precise observations using the HARPS spectrograph at the ESO 3.6-metre telescope at La Silla, Chile, have now not only detected the motion of the spots due to the rotation of Ceres about its axis, but also found unexpected additional variations suggesting that the material of the spots is volatile and evaporates in sunlight.
This artist's impression is based on a detailed map of the surface compiled from images taken from NASA's Dawn spacecraft in orbit around the dwarf planet Ceres. It shows the very bright patches of material in the crater Occator and elsewhere. New observations using the HARPS spectrograph on the ESO 3.6-metre telescope at La Silla in Chile have revealed unexpected daily changes on these spots, suggesting that they change under the influence of sunlight as Ceres rotates.
Credit: ESO/L.Calçada/NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/Steve Albers/N. Risinger (skysurvey.org)
The lead author of the new study, Paolo Molaro, at the INAF-Trieste Astronomical Observatory , takes up the story: "As soon as the Dawn spacecraft revealed the mysterious bright spots on the surface of Ceres, I immediately thought of the possible measurable effects from Earth. As Ceres rotates the spots approach the Earth and then recede again, which affects the spectrum of the reflected sunlight arriving at Earth."
Ceres spins every nine hours and calculations showed that the velocities of the spots towards and away from the Earth due to this rotation would be very small, of order 20 kilometres per hour. But this motion is big enough to be measurable via the Doppler effect with high-precision instruments such as HARPS.
The team observed Ceres with HARPS for a little over two nights in July and August 2015. "The result was a surprise," adds Antonino Lanza, at the INAF-Catania Astrophysical Observatory and co-author of the study. "We did find the expected changes to the spectrum from the rotation of Ceres, but with considerable other variations from night to night."
The team concluded that the observed changes could be due to the presence of volatile substances that evaporate under the action of solar radiation . When the spots inside the Occator crater are on the side illuminated by the Sun they form plumes that reflect sunlight very effectively. These plumes then evaporate quickly, lose reflectivity and produce the observed changes. This effect, however, changes from night to night, giving rise to additional random patterns, on both short and longer timescales.
If this interpretation is confirmed Ceres would seem to be very different from Vesta and the other main belt asteroids. Despite being relatively isolated, it seems to be internally active . Ceres is known to be rich in water, but it is unclear whether this is related to the bright spots. The energy source that drives this continual leakage of material from the surface is also unknown.
Dawn is continuing to study Ceres and the behaviour of its mysterious spots. Observations from the ground with HARPS and other facilities will be able to continue even after the end of the space mission.
 Bright spots were also seen, with much less clarity, in earlier images of Ceres from the NASA/ESA Hubble Space Telescope taken in 2003 and 2004.
 It has been suggested that the highly reflective material in the spots on Ceres might be freshly exposed water ice or hydrated magnesium sulphates.
 Many of the most internally active bodies in the Solar System, such as the large satellites of Jupiter and Saturn, are subjected to strong tidal effects due to their proximity to the massive planets.
This research was presented in a paper entitled "Daily variability of Ceres' Albedo detected by means of radial velocities changes of the reflected sunlight", by P. Molaro et al., which appeared in the journal Monthly Notices of the Royal Astronomical Society.
The team is composed of P. Molaro (INAF-Osservatorio Astronomico di Trieste, Trieste, Italy), A. F. Lanza (INAF-Osservatorio Astrofisico di Catania, Catania, Italy), L. Monaco (Universidad Andres Bello, Santiago, Chile), F. Tosi (INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Rome, Italy), G. Lo Curto (ESO, Garching, Germany), M. Fulle (INAF-Osservatorio Astronomico di Trieste, Trieste, Italy) and L. Pasquini (ESO, Garching, Germany).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world's most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. 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, the world's most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world's largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become "the world's biggest eye on the sky".
INAF-Osservatorio Astronomico di Trieste
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Richard Hook | EurekAlert!
New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology
Light rays from a supernova bent by the curvature of space-time around a galaxy
21.04.2017 | Stockholm University
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
Two researchers at Heidelberg University have developed a model system that enables a better understanding of the processes in a quantum-physical experiment...
Glaciers might seem rather inhospitable environments. However, they are home to a diverse and vibrant microbial community. It’s becoming increasingly clear that they play a bigger role in the carbon cycle than previously thought.
A new study, now published in the journal Nature Geoscience, shows how microbial communities in melting glaciers contribute to the Earth’s carbon cycle, a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
21.04.2017 | Physics and Astronomy
21.04.2017 | Health and Medicine
21.04.2017 | Physics and Astronomy