Planetologists presented the results of studies of the third-largest impact crater Urvara on the dwarf planet Ceres. The results of the work confirm the hypothesis that Ceres was and is still a geologically active world, and salts and organic matter played an important role in its evolution.
Everything you need to know about Ceres
Ceres is the largest (940 kilometers in diameter) object in the main asteroid belt. It was formed in the earliest period of the formation of the solar system, therefore, understanding its internal structure and composition allows us to get an idea of the formation and evolution of the embryos of planets rich in volatile substances that arose in the protoplanetary disk.
From 2015 to 2018, the automatic station Dawn worked in orbit of the dwarf planet, which collected a huge amount of unique scientific data, in particular, it became known that Ceres demonstrates cryovolcanic activity and consists of a thin layer of regolith and ice crust, formed due to the freezing of the ancient water ocean, mantle, and core.
Analysis of the Urvara crater
A team of planetary scientists led by Andreas Nathues of the Max Planck Institute for Solar System Research has published the results of an analysis of high-resolution imagery and Dawn VIR spectrometer observations of the ancient Urvara impact basin.
With a diameter of 170 kilometers, this is the third-largest impact structure on Ceres, the study of which allows you to learn more about the crust of the dwarf planet. The age of the crater has been estimated at 250 million years, while the difference between the age of the crater and the age of its southern part is 100 million years.
The crater is located at the transition between the equatorial zone with a smooth relief and high latitudes, where the surface relief is rougher.
The crater has well-defined walls of variable height, with extensive terraces to the south and steep escarpments to the north and northeast.
The central pit of the crater has a diameter of 20 kilometers and a depth of 0.56 kilometers, such structures require a high content of volatile substances in the crust.
The central ridge is not located in the center of the crater and is approximately three kilometers high, with multiple bright granular flows visible on its flanks, which originate from small bright outcrops of rock. The ridge marks the highest part of the extended structure that separates the uplifted northern tier of the crater from the southern one.
The ledges on it have a block structure and demonstrate the presence of boulders and talus. Central ridges have been observed in many of Ceres’ large craters, possibly formed from oblique collisions or being the remnants of collapsed central peaks. In the case of Urvara, the central ridge is more likely a remnant of the collapsed central peak, and not the result of an oblique impact, and may contain substances raised from depths of up to 50 kilometers.
Salt deposits and organic compounds exist in Ceres’ craters
In particular, concentrated outcrops of bright material (salts), several meters thick, observed along the upper central ridge of the crater may originate from subsurface brine reservoirs and be the result of cryovolcanism or uplift of the brine layer with subsequent evaporation of water. However, it remains to be explained why salt deposits are found mainly on the central ridge and not at the bottom of the crater.
One of the deepest areas in Urwara south of the central ridge shows an undulating, heterogeneous topography with numerous shallow depressions, possibly formed by degassing of volatile-rich subsurface layers, consistent with the idea that the central pit originated from the partial collapse of the crater’s central peak.
The outcrops of the central ridge differ in their spectral characteristics from the famous bright spots in the Occator crater, which indicates a different composition of salts. In addition, scientists have found a curious area of 0.1×0.5 kilometers on the western floor of the crater, which is located on a ledge and demonstrates the presence of fine-grained material rich in organic matter.
However, there are no obvious signs that the material was exposed due to impact. This is the first such find on Ceres outside and around the Ernutet crater.
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Sources:
• Max Planck Institute for Solar System Research. (2022, February 22). Organic compounds on Ceres.
• Nathues, A., Hoffmann, M., Schmedemann, N., Sarkar, R., Thangjam, G., Mengel, K., Hernandez, J., Hiesinger, H., & Pasckert, J. H. (2022, February 22). Brine residues and organics in the Urvara Basin on Ceres. Nature News.
• O’Neill, M. (2022, February 27). Salt deposits and organic compounds discovered on dwarf planet ceres. SciTechDaily.
• Prostak, S. (n.d.). Dawn Detects Organics and Salts in Giant Crater on Ceres.
