“Life on Dwarf Planet Ceres?” Mysterious Daily Changes in Bright Spots Baffle Scientists

 

 

Ceres-white-spot

 

Bright spots on the dwarf planet Ceres continue to stump  researchers, led by Paolo Molaro of the Trieste Astronomical Observatory in Italy, who conducted the observations using the HARPS spectrograph at ESO’s La Silla Observatory in Chile. Molaro’s team made an unexpected discovery: Although Ceres appears as little more than a point of light from the Earth, very careful study of its light shows not only the changes expected as Ceres rotates, but also that the spots brighten during the day and also show other variations. These observations suggest that the material of the spots is volatile and evaporates in the warm glow of sunlight.


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 [1]. 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 neighbors.

 

The bright spots near the center of Ceres’ Occator crater are shown above in enhanced color from NASA’s Dawn robotic spacecraft. Lower resolution color data have been overlaid onto a higher resolution view of the crater. The view was produced by combining the highest resolution images of Occator obtained in February 2016 with color images obtained in September 2015. The three images used to produce the color were taken using spectral filters centered at 438, 550 and 965 nanometers. Dawn’s close-up view reveals a dome in a smooth-walled pit in the bright center of the crater. Numerous linear features and fractures crisscross the top and flanks of this dome. (NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / PSI / LPI).

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.

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.”

“We know nothing about these changes, really. And this increases the mystery of these spots,” Molaro told Astrowatch.net. “It is already well known that a lot of water hides beneath the surface of Ceres, so water ice or clathrates hydrates are the most natural hypotheses. But a proper answer will be hopefully provided by scientists working in the Dawn team in the coming months,” Molaro said. “Life as we know it on Earth needs liquid water, biogenic elements and a stable source of energy. Is Ceres a good place to have these things simultaneously and for a substantial amount of time, like billions of years? Nobody knows at the moment,” he added.

Ceres, below, seen by the Dawn space probe on Jan. 13, 2015, in optical light and infrared (right). In the infrared image, white indicates hotter than red.

 

Ceres-visible-infrared-light

 

Ceres spins every nine hours and calculations showed that the effects due to the motion of the spots towards and away from the Earth caused by this rotation would be very small, of order 20 kilometers 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. It has been suggested that the highly reflective material in the spots on Ceres might be freshly exposed water ice or hydrated magnesium sulphates. 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. 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.

Dawn is continuing to study Ceres and the behavior 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.

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 Daily Galaxy via ESO and Astrowatch.net

Image credits: ESO, NASA/JPL-Caltech/UCLA/ASI/INAF

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