2026-01-26 インペリアル・カレッジ・ロンドン（ICL）
Perseverance views potential shoreline deposits in the Eastern Margin Unit with Mastcam-Z on Sol 934 (Credit: NASA/JPL-Caltech/ASU/MSSS).
＜関連情報＞
- https://www.imperial.ac.uk/news/articles/engineering/earth-science/2026/new-clues-to-marss-habitability-in-discovery-of-ancient-beach/
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025JE009420
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025JE009111
- https://www.science.org/doi/10.1126/science.adu8264
火星ネレトヴァ渓谷ジェゼロクレーター入江に保存された河川湖沼環境 A Fluvio-Lacustrine Environment Preserved in the Jezero Crater Inlet Channel, Neretva Vallis, Mars
Alexander J. Jones, Robert Barnes, Sanjeev Gupta, Gerhard Paar, Joel Hurowitz, Brittan V. Wogsland, Adrian Broz, Hemani Kalucha, Athanasios Klidaras, Kathryn M. Stack, Patrick Russell,…
Journal of Geophysical Research: Planets Published: 08 January 2026
DOI:https://doi.org/10.1029/2025JE009420
Abstract
Martian fluvial valleys provide evidence for the surface flow of liquid water, making them a key target for rover-based investigations of ancient habitability. The Mars 2020 Perseverance rover spent ∼85 sols exploring the Bright Angel formation, exposed across the floor of Neretva Vallis: the western inlet channel of Jezero crater. This study documents the sedimentology and stratigraphy of the Bright Angel formation to reconstruct its depositional setting. The unit preserves a concave-up bedding structure consistent with a young channel-fill deposit, rather than an older unit exposed by incision of Neretva Vallis. The lower stratigraphy displays a fining-up sequence from coarse-grained sediments up to pebble-conglomerates (the Tuff Cliff member) into a ≥10-m-thick succession of laminated mudstone (the Walhalla Glades member), interpreted as a transgressive sequence recording the onset of lacustrine conditions in Neretva Vallis. Lenses of matrix-supported granule-conglomerate adjacent to the valley wall (the Fern Glen Rapids member) may preserve locally derived debris flows entering the lake. These are overlain by a polymict, matrix-supported, boulder-conglomerate (the Mount Spoonhead member), interpreted as a high-energy debrite derived from the watershed. The sequence is capped by cross-stratified sediments (the Serpentine Rapids member), preserving lake margin deposits. The Bright Angel lacustrine sequence occurs ∼10–50 m higher in elevation than the lake level anticipated for the Jezero western delta, requiring an additional period of lacustrine activity. The structure and spatial distribution of the unit leads us to propose that a late-stage blockage of Neretva Vallis may have facilitated the formation of a perched, valley-confined lake upstream.
Plain Language Summary
Between June and August 2024, the Perseverance rover investigated sedimentary rocks exposed in a dried-up river valley that once fed an ancient lake in Jezero crater, Mars. This study analyses image data collected by Perseverance to describe these rocks, called the “Bright Angel” formation, and determine their depositional environment. Layers of rock in the Bright Angel formation are inclined into the center of the channel, suggesting they were deposited into the valley rather than being an older rock unit exposed by erosion of the channel. Somewhat surprisingly, most of the Bright Angel formation consists of fine-grained, thinly layered mudstone deposited in a calm, lake setting by suspension settling of clay- and silt-sized particles, rather than sediment consistent with river deposits. Rock units with pebbles and cobbles mixed with mudstone were most likely deposited as muddy debris flows entering the lake. Other pebble-rich rocks near the edge of the valley preserve evidence for currents generated by flowing water, and were likely laid down at the lake margin by rivers. These lake deposits sit tens of meters above the lake level expected at Jezero crater, suggesting a blockage may have dammed the valley, forming a separate, upstream lake confined to the channel.
Key Points
- The Bright Angel formation preserves diverse, mudstone-dominated sedimentary facies indicative of a fluvio-lacustrine environment
- 3D bedding measurements indicate that the valley floor unit has a concave-up structure, consistent with a young, channel-fill deposit
- Lacustrine conditions may have been facilitated by a blockage of Neretva Vallis, leading to the formation of a valley-confined lake
火星ジェゼロクレーター縁辺部の炭酸塩岩石の地層学：海岸線のプロセスの証拠か？ Stratigraphy of Carbonate-Bearing Rocks at the Margin of Jezero Crater, Mars: Evidence for Shoreline Processes?
Alexander J. Jones, Sanjeev Gupta, Robert Barnes, Briony H. N. Horgan, Kenneth H. Williford, Gerhard Paar, Kathryn. M. Stack, Bradley J. Garzcynski, Eleni Ravanis,…
Journal of Geophysical Research: Planets Published: 06 January 2026DOI:https://doi.org/10.1029/2025JE009111
Abstract
Martian carbonate-bearing rocks are compelling targets for exploration because they preserve detailed records of past aqueous processes, climate, and habitability. The Margin unit in Jezero crater is a distinct olivine- and carbonate-bearing unit stratigraphically underlying the western fan, lining the inner margin of the western crater rim and has a contested origin. Perseverance spent ∼350 sols investigating the unit as part of its fourth mission campaign, aiming to constrain its origin, alteration history and biosignature preservation potential. This study reports on the lithofacies and stratigraphy of the unit by analyzing Mastcam-Z mosaics and derived 3D outcrop models, supplemented by long-distance SuperCam observations and detailed textural analyses from SHERLOC WATSON and ACI images. We find that the Margin unit comprises two distinct sub-units. The Eastern Margin Unit (EMU) comprises well-stratified, low-angle basinward-, rimward- and sub-horizontally inclined medium-grained sandstones which preserve angular to rounded grains, occasional cross-stratification, convex-up bedding, and erosion surfaces. The Western Margin Unit (WMU) comprises distinctly structureless to decimeter-scale parallel-layered rocks which drape the crater rim and are inclined into the crater. The origin of the WMU is uncertain but may be most consistent with a variably carbonated olivine cumulate. The favored depositional model for the EMU is a lacustrine shore zone environment where sediments derived from the adjacent WMU have been locally reworked by wave action along a paleoshoreline at around –2,400 m elevation. These observations suggest that the Margin unit preserves diverse subsurface and surface aqueous environments and further extends the habitability window at Jezero crater.
Plain Language Summary
Carbonate minerals are rare on Mars and are important targets because they preserve information about ancient climates, water availability, and habitable environments. NASA’s Mars 2020 Perseverance rover spent around one Earth year exploring the “Margin unit”, a geologic unit lining the inner crater rim west of the Jezero delta, rich in olivine and carbonate-minerals. Here, we use images acquired by Perseverance to describe the Margin unit rocks and consider how they formed. The Margin unit primarily consists of structureless to thick-layered rocks with compositions and textures suggesting they have experienced significant alteration by subsurface circulating water. This alteration makes determining their origin challenging, but their overall structure, texture, composition and distribution appear most consistent with an igneous origin, formed by crystal settling in a cooling body of molten rock. At lower elevations in the east, the Margin unit displays rounded grains and sedimentary structures consistent with a lake shore environment. These rocks are interpreted as a sandy veneer reworked from the bulk of the Margin unit by waves at the Jezero lake shoreline. These observations show that the Margin unit preserves multiple ancient, and potentially habitable, settings, including water-rich surface and subsurface environments.
Key Points
- The Margin unit underlies the Jezero Western fan, drapes the inner crater rim and may record both igneous and sedimentary lithofacies
- Most of the unit comprises structureless to planar-layered rocks, which most likely preserve an aqueously altered olivine cumulate
- In the east of the unit, rounded grains and sedimentary structures indicate reworking by waves along the shoreline of the Jezero paleolake
火星のジェゼロクレーターの炭酸塩超塩基性火成岩 Carbonated ultramafic igneous rocks in Jezero crater, Mars
Kenneth H. Williford, Kenneth A. Farley, Briony H.N. Horgan, Brad Garczynski, […] , and R. Aileen Yingst
Science Published:17 Dec 2025
DOI:https://doi.org/10.1126/science.adu8264
Abstract
The Perseverance rover landed in Jezero crater on Mars, which once contained a lake of liquid water. We report the rock properties encountered by Perseverance during a ten-kilometer traverse extending over 400 meters in elevation, from beneath Jezero’s western sedimentary fan to the upper crater rim. These rocks consist of coarse-grained olivine, magnesium- and iron-carbonates, silica, and phyllosilicates, including some of the oldest materials exposed within Jezero. We infer these rocks formed by olivine accumulation in an igneous system of layered intrusions, followed by exposure to water and carbon dioxide that caused extensive carbonation of the silicate minerals. Aqueous alteroverlingation is more pronounced at lower elevations. Higher elevation exposures on the crater rim appear similar to olivine-rich rocks distributed over the wider Nili Fossae region.
