Evidence of an oceanic impact and megatsunami sedimentation in Chryse Planitia, Mars

In 1976, NASA's Viking 1 Lander (V1L) was the first spacecraft to operate successfully on the Martian surface. The V1L landed near the terminus of an enormous catastrophic flood channel, Maja Valles. However, instead of the expected megaflood record, its cameras imaged a boulder-strewn surface of elusive origin. We identified a 110-km-diameter impact crater (Pohl) ~ 900 km northeast of the landing site, stratigraphically positioned (a) above catastrophic flood-eroded surfaces formed ~ 3.4 Ga during a period of northern plains oceanic inundation and (b) below the younger of two previously hypothesized megatsunami deposits. These stratigraphic relationships suggest that a marine impact likely formed the crater. Our simulated impact-generated megatsunami run-ups closely match the mapped older megatsunami deposit's margins and predict fronts reaching the V1L site. The site's location along a highland-facing lobe aligned to erosional grooves supports a megatsunami origin. Our mapping also shows that Pohl's knobby rim regionally represents a broader history of megatsunami modification involving circum-oceanic glaciation and sedimentary extrusions extending beyond the recorded megatsunami emplacement in Chryse Planitia. Our findings allow that rocks and soil salts at the landing site are of marine origin, inviting the scientific reconsideration of information gathered from the first in-situ measurements on Mars

Gridmapping the northern plains of Mars: Geomorphological, Radar and Water-Equivalent Hydrogen results from Arcadia Plantia

A project of mapping ice-related landforms was undertaken to understand the role of sub-surface ice in the northern plains. This work is the first continuous regional mapping from CTX (“ConTeXt Camera”, 6 m/pixel; Malin et al., 2007) imagery in Arcadia Planitia along a strip 300 km across stretching from 30°N to 80°N centred on the 170° West line of longitude. The distribution and morphotypes of these landforms were used to understand the permafrost cryolithology. The mantled and textured signatures occur almost ubiquitously between 35° N and 78° N and have a positive spatial correlation with inferred ice stability based on thermal modelling, neutron spectroscopy and radar data. The degradational features into the LDM (Latitude Dependent Mantle) include pits, scallops and 100 m polygons and provide supporting evidence for sub-surface ice and volatile loss between 35-70° N in Arcadia with the mantle between 70-78° N appearing much more intact. Pitted terrain appears to be much more pervasive in Arcadia than in Acidalia and Utopia suggesting that the Arcadia study area had more wide-spread near-surface sub-surface ice, and thus was more susceptible to pitting, or that the ice was less well-buried by sediments. Correlations with ice stability models suggest that lack of pits north of 65-70° N could indicate a relatively young age (~1Ma), however this could also be explained through regional variations in degradation rates. The deposition of the LDM is consistent with an airfall hypothesis however there appears to be substantial evidence for fluvial processes in southern Arcadia with older, underlying processes being equally dominant with the LDM and degradation thereof in shaping the landscape

Understanding Martian megaflood-infiltration Landscapes at Hebrus Valles through Laboratory Experiments

International audienceMost of the Martian outflow channels have terminal areas buried beneath the younger sediments of the northern plains. Hebrus Valles, situated SE of Utopia Planitia, is exceptional in that its lowermost areas shows an abrupt disappearance of channels into a large cluster of pits. Our study aims to document the possibility of Hebrus Valles interacting with some preexisting underground cavernous networks. We conducted a series of flume experiments to simulate infiltration, including polygonally tunneling buried in sand. To replicate the Hebrus morphology, we constructed an orthogonal pattern of ice slabs before the experimentation, which after melting, simulated cave geometries. Our results reproduce incision features like those at the terminus of Hebrus Valles, implying that these discontinuities facilitated underground conduit generation. Our results provide the first laboratory-based confirmation of this type of catastrophic flood with infiltration processes inferred from remote-sensing observations. Our laboratory results show that floods are captured by sinkholes and can deliver a regional interconnection of channels and caves, which should have contributed actively to the dynamic of such floodwater infiltration in Hebrus Valles. Reference: Costard, F., Rodriguez, JAP, E. Godin, A. Séjourné, & J. Kargel. (2024). Deciphering Martian Flood Infiltration Processes at Hebrus Valles: Insights from Laboratory Experiments and Remote Sensing Observations. J. Geophys. Res. Planets. 129, e2023JE007770, doi/10.1029/2023JE0077

Variability of the thermal regime of the frozen islands in the Lena floodplain, Yakutia

International audience<p>In Yakutia, the Lena River is one of the largest fluvial hydrosystems within the periglacial zone with thick and continuous permafrost. The Lena River and its tributaries are characterized by a large inter-annual variability with a thawing of the ice cover, inducing huge ice-jams and a fast rising of the water level, together with an active process of thermal and mechanical erosion. During spring floods, the islands along the Lena River channel are submerged and this induces an additional thermal imprint. Ten islands upstream of the city of Yakutsk have been monitored during two consecutive years (July 2009 to July 2011). We measured the frozen soil thermal regime and water temperatures of these islands on a daily basis using automated waterproof data loggers. Other sensors are used to estimate the height and duration of flooding. We examine the effect of repeated inundations and warm stream water on the thermal regime of frozen islands as well as the effect of the duration of the flood season. Our measurement campaigns revealed that the effect of island submersion at the time of break-up appears to have a relatively moderated impact on the frozen soil thermal profile at depth. The results also show that the Lena floodplain is thermally heterogeneous with islands composed of permafrost and others with only seasonally frozen ground. Our study shows that relatively young (less than 30 years old) islands, composed of fine sand material appear less prone to permafrost formation compared to older islands with ice-rich silty material.</p&gt

Tsunami on Mars: Implications for the duration and timing of a northern ocean

International audience<p>The duration and timing of a northern ocean is a key issue in understanding the past geological and climatic evolution of Mars. Mars experienced its greatest loss of H<sub>2</sub>O between the Noachian and Late Hesperian (~10 m Global Equivalent Layer, Jakosky et al., 2017) roughly the same amount that is thought to have been added to the global inventory by extrusive volcanism over the same time period (Carr and Head, 2015). Thus, the total inventory of water was probably similar during these two epochs. But, the ocean during the Late Hesperian was smaller in extension than the ocean during the Noachian– with significant implications for the potential origin and survival of life. Here we examine the implications of the existence of a Late Hesperian/ Early Amazonian ocean on the planet’s inventory of water (and especially liquid water) and its variation with time. Our previous work (Rodriguez et al., 2016; Costard et al., 2017) concluded that the most plausible explanation for the origin of the Thumbprint Terrain (TT) lobate deposits, with run-ups, found along the dichotomy boundary, especially in Arabia Terra, was tsunami deposits. This supports the hypothesis that an ocean occupied the northern plains of Mars as recently as ~3 billion years ago. Furthermore, Costard et al (2017) produced a tsunami numerical model showing that the TT deposits exhibit fine-scale textural patterns due to the wave’s interference patterns resulting from interactions with the coastal topography. More recently, we suggested that the unusual characteristics of Lomonosov crater (50.52°N/16.39°E ) in the northern plains are best explained by the presence of a shallow ocean at the time of the impact (Costard et al., 2019). Interestingly, the apparent agreement between the age of the Lomonosov impact and that of the TT unit (~3 Ga), strongly suggests that it was the source of the tsunami (Costard et al., 2019). Our preliminary assessment indicates that this impact-generated tsunami required a mostly liquid ocean and because of the high latitude location of the Lomonosov crater site, our results strongly imply relatively warm paleoclimatic conditions. Our conclusions highlight the need for more sophisticated climate models.</p&gt

Orientation and distribution of recent gullies in the southern hemisphere of Mars: Observations from High Resolution Stereo Camera/Mars Express (HRSC/MEX) and Mars Orbiter Camera/Mars Global Surveyor (MOC/MGS) data Camera/Mars Express (HRSC/MEX) and Mars Orbiter Camera/Mars Global Surveyor (MOC/MGS) data

Geologically recent small gullies on Mars display morphologies consistent with erosion by water or by debris flows. Suggested formation models are divided into two main categories: (1) groundwater or (2) melting of near-surface ice/snow sourced from the atmosphere. We have measured location and orientation and recorded the local contexts of gullies to constrain the likely models of gully formation. More than 22,000 Mars Orbiter Camera Narrow Angle (MOC NA) and >120 Mars Express High Resolution Stereo Camera (HRSC) images in the southern hemisphere were searched for gullies. Discrete gullied slope sections with consistent orientation were recorded rather than individual gullies. Slope setting (impact crater, valley wall, etc.), location, and orientation were recorded for each slope section. More than 750 MOC images with gullies (>900 distinct gullied slope sections) and more than 40 HRSC images (>380 distinct gullied slope sections) were identified. From both MOC and HRSC, gullies were found to be most common between 30 and 50 degrees latitude and to have an overall pole facing preference. The preferred gully orientation for HRSC is southeast rather than south in MOC, owing to illumination effects that make gullies difficult to detect on south- to southwest-facing slopes in HRSC. In both MOC and HRSC surveys, higher-latitude gullies show less preference for pole facing than those at mid latitudes. Both data sets produced similar results, demonstrating that our data are reliable. We suggest that the observed latitudinal and orientation distributions of gullies show that insolation and atmospheric conditions play a key role in gully formation

Standardizing the nomenclature of Martian impact crater ejecta morphologies

International audienceThe Mars Crater Morphology Consortium recommends the use of a standardized nomenclature system when discussing Martian impact crater ejecta morphologies. The system utilizes nongenetic descriptors to identify the various ejecta morphologies seen on Mars. This system is designed to facilitate communication and collaboration between researchers. Crater morphology databases will be archived through the U.S. Geological Survey in Flagstaff, where a comprehensive catalog of Martian crater morphologic information will be maintained