2024-12-20 NASA
NASA’s Dawn spacecraft captured this image of Vesta as it left the giant asteroid’s orbit in 2012. The framing camera was looking down at the north pole, which is in the middle of the image. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
＜関連情報＞
- https://www.nasa.gov/missions/dawn/lab-work-digs-into-gullies-seen-on-giant-asteroid-vesta-by-nasas-dawn/
- https://iopscience.iop.org/article/10.3847/PSJ/ad696a
- https://www.sciencedirect.com/science/article/abs/pii/S0012821X14007572
ベスタにおける過渡的な水流の地形学的証拠 Geomorphological evidence for transient water flow on Vesta
Jennifer E.C. Scully, Christopher T. Russell, An Yin, Ralf Jaumann, Elizabeth Carey, Julie Castillo-Rogez, Harry Y. McSween, Carol A. Raymond, Vishnu Reddy, Lucille Le Corre
Earth and Planetary Science Letters Available online: 19 December 2014
DOI:https://doi.org/10.1016/j.epsl.2014.12.004
Highlights
- We identify two types of gullies on Vesta: curvilinear and linear.
- We propose transient water forms curvilinear gullies that end in lobate deposits.
- A debris-flow-like process (≤30% water) is proposed to form curvilinear gullies.
- Impact-heating of ice-bearing sub-surface deposits likely releases the water.
- Quantitative modeling and experiments support this hypothesis.
Abstract
Vesta, the second most massive asteroid, has long been perceived as anhydrous. Recent studies suggesting the presence of hydrated minerals and past subsurface water have challenged this long-standing perception. Yet, direct geologic indications of water activity on Vesta’s surface were unexpected. Herein we show evidence that transient water flowed on the surface, in a debris-flow-like process, and left distinctive geomorphologic features. Based on detailed analysis of highest-resolution (∼20 m/pixel) images obtained by the Dawn spacecraft, we identify a class of locally occurring, interconnected and curvilinear gully networks on the walls of young (< hundreds of Ma) impact craters, ending in lobate deposits near the crater floors. As curvilinear systems only occur within impact craters, we propose that they formed by a particulate-dominated flow of transient water that was released from buried ice-bearing deposits by impact-induced heating and melting. This interpretation is in accordance with the occurrence of pitted terrain on lobate deposits and crater floors. Pitted terrain is proposed to result from the degassing of volatiles. The proposed buried ice-bearing deposits are likely localized in extent and may be currently extant in Vesta’s subsurface. Together with the discovery of water evaporation on Ceres and water activity on several small asteroids, our results support the new paradigm that water is widespread in the asteroid belt.
空気のない世界における衝突後の塩水と水の寿命の実験的検討 Experimental Examination of Brine and Water Lifetimes after Impact on Airless Worlds
Michael J. Poston, Samantha R. Baker, Jennifer E. C. Scully, Elizabeth M. Carey, Lauren E. Mc Keown, Julie C. Castillo-Rogez and Carol A. Raymond
The Planetary Science Journal Published 2024 October 21
DOI:10.3847/PSJ/ad696a
Abstract
The role played by transient impact-induced endogenous brines in the formation of geomorphic features has been proposed on airless worlds such as Europa, Vesta, and Ceres, as well as on worlds with thin atmospheres such as Mars. After liquefaction, the hypothesized brines flow in a debris-flow-like process, incising curvilinear gullies and constructing lobate deposits within newly formed craters. Here we investigate what parameters (if any) could enable liquid to be transiently present for a sufficient time (∼tens of minutes) under postimpact transient atmospheric pressures (10−4–10−5 torr) to form curvilinear gullies and lobate deposits, as have been seen on Vesta and more tentatively Ceres. We report that water likely vacuum-freezes too quickly, while NaCl brine enables flow longevity. We also find that frozen lid formation facilitates longer liquid lifetimes, as with lava in terrestrial lava tubes and model predictions for cryovolcanic flows on Europa. This work provides additional contributions to the growing body of literature that investigates the role of transient brines in sculpting the surfaces of airless worlds.
