Thanks to data from NASA spacecraft Dawn (“Dawn”), Ceres reveals some of his well-kept secrets, according to two new studies in the journal Nature. They include the long-awaited speculation about a mysterious bright features that can be detected over the entire surface of the dwarf planet. In one study, scientists determined that the bright material as a kind of salt. The second is supposed identification of ammonia-rich clays, raising questions about the formation of Ceres.
About bright spots
On Ceres more than 130 bright areas, and most of them are associated with craters. The study authors led by Andreas Nachesom from the Institute of Solar system research max Planck in göttingen, Germany, write that the bright material corresponds to the type of magnesium sulfate called hexahydric. Another type of magnesium sulfate on Earth known as Epsom salt.
Natues and colleagues, armed with snapshots of the HR camera Dawn, suggest that these areas rich with salt left after water ice sublimated in the past. The fall of the asteroid revealed a mixture of ice and salt, they say.
“The global nature of the bright spots of Ceres suggests that this world has an underground layer that contains salt water ice,” says Nathues.
A new look at Akator
The surface of Venus, the average diameter of 940 km, mostly dark — similar in brightness to the fresh asphalt, the study authors write. Bright spots scattered on the surface, represent a wide range of brightness, reflecting up to 50% of the sunlight. However, water ice on Ceres was clearly detected; the required data in high resolution to clarify this issue.
The inner part of the crater Ocator contains the brightest materials on Ceres. Ocator 90 kilometers in diameter, and its Central pit, covered with this colourful material, a width of 10 kilometers and a depth of 0.5 kilometers. Dark streaks, possibly, faults, cross the pit. The remains of a Central peak, which was up to 0.5 kilometer in height, too it is possible to see.
With its sharp rim and walls, as well as abundant terraces, and landslide deposits, Akator is among the youngest features of Ceres. The Dawn mission scientists estimate its age to be 78 million years.
The study’s authors write that some species of Akatora reveal a diffuse fog near the surface, which fills the crater bottom. This may be related to observations of water vapor on Ceres, conducted by the space Observatory Herschel in 2014. Haze, it seems, there is at midday local time and is absent at dawn and at sunset, the authors write. This suggests that the phenomenon is reminiscent of the activity on the surface of the comet, when steam picks up tiny dust particles and ice. Further data analysis will allow to test this hypothesis and to shed light on the process behind this activity.
“Dawn science team is still discussing these results and analyzes the data to better understand what is happening in Accatone,” says Chris Russell, principal investigator of the Dawn mission.
The importance of ammonia
In the second study Nature members of the research group Dawn looked at the composition of Ceres, and found the presence of ammonia-rich clays. They used data from the visible and infrared spectrometer, a device that detects wavelengths reflected from the surface, and based on them identifies the minerals.
Ammonia ice itself will evaporate on Ceres now, because the dwarf planet is too warm. However, molecules of ammonia are stable, if will be combined (chemically bound) with other minerals.
The presence of ammonium compounds increases the likelihood that Ceres was born in the main asteroid belt between Mars and Jupiter, where at the present time, but instead formed in the outer Solar system. Another idea that Ceres formed close to its current position, including the materials that arrived from the outer Solar system near the orbit of Neptune, where the nitrogen ice is thermally stable.
“The presence of ammonia-containing compounds suggests that Ceres is composed of material that is gathered in an environment rich in ammonia and nitrogen. Consequently, we believe that this material originated in the cold outer Solar system,” says Maria Cristina de Sanctis, lead author of the study from the National Institute for astrophysics in Rome.
Comparing the spectrum of the light reflected from Ceres and meteorites, scientists have discovered some similarities. In particular, with the spectrum — the chemical fingerprint — of carbonaceous chondrites, carbon-rich meteorites, which are considered a suitable analogue for the dwarf planet. But the coincidences are observed with all wavelengths, the tools gathered, the researchers note. In particular, the distinctive absorption bands corresponding to the mixtures with saturated ammonium minerals associated with wavelengths that cannot be observed using ground based telescopes.
Scientists noted another difference is that these carbonaceous chondrites contain from 15 to 20 percent water, then its content on Ceres is up to 30 percent.
“It is possible that Ceres has retained more volatiles than these meteorites, or could pull water from volatile-rich materials,” says de Sanctis.
The study also shows that the daytime surface temperature on Ceres range from -93 to -32 degrees Celsius. Maximum temperatures were measured in the Equatorial region. Temperatures at the equator and near in General too high to support the existence of ice on the surface for a long time, say the authors, but this needs to be clarified with future Dawn data.