Estimating precipitation on early Mars using a radiative-convective model of the atmosphere and comparison with inferred runoff from geomorphology

We compare estimates of atmospheric precipitation during the Martian Noachian-Hesperian boundary 3.8 Gyr ago as calculated in a radiative-convective column model of the atmosphere with runoff values estimated from a geomorphological analysis of dendritic valley network discharge rates. In the atmospheric model, we assume CO2-H2O-N2 atmospheres with surface pressures varying from 20 mb to 3 bar with input solar luminosity reduced to 75% the modern value. Results from the valley network analysis are of the order of a few mm d-1 liquid water precipitation (1.5-10.6 mm d-1, with a median of 3.1 mm d-1). Atmospheric model results are much lower, from about 0.001-1 mm d-1 of snowfall (depending on CO2 partial pressure). Hence, the atmospheric model predicts a significantly lower amount of precipitated water than estimated from the geomorphological analysis. Furthermore, global mean surface temperatures are below freezing, i.e. runoff is most likely not directly linked to precipitation. Therefore, our results strongly favor a cold early Mars with episodic snowmelt as a source for runoff. Our approach is challenged by mostly unconstrained parameters, e.g. greenhouse gas abundance, global meteorology (for example, clouds) and planetary parameters such as obliquity- which affect the atmospheric result - as as well as by inherent problems in estimating discharge and runoff on ancient Mars, such as a lack of knowledge on infiltration and evaporation rates and on flooding timescales, which affect the geomorphological data. Nevertheless, our work represents a first step in combining and interpreting quantitative tools applied in early Mars atmospheric and geomorphological studies.Comment: accepted in Planetary and Space Science, 37 pages, 14 figures, 2 table

Periodic Bedrock Ridges at the ExoMars 2022 Landing Site: Evidence for a Changing Wind Regime

Wind-formed features are abundant in Oxia Planum (Mars), the landing site of the 2022 ExoMars mission, which shows geological evidence for a past wet environment. Studies of aeolian bedforms at the landing site were focused on assessing the risk for rover trafficability, however their potential in recording climatic fluctuations has not been explored. Here we show that the landing site experienced multiple climatic changes in the Amazonian, which are recorded by an intriguing set of ridges that we interpret as Periodic Bedrock Ridges (PBRs). Clues for a PBR origin result from ridge regularity, defect terminations, and the presence of preserved megaripples detaching from the PBRs. PBR orientation differs from superimposed transverse aeolian ridges pointing toward a major change in wind regime. Our results provide constrains on PBR formation mechanisms and offer indications on paleo winds that will be crucial for understanding the landing site geology

The PanCam instrument on the 2018 Exomars rover: Scientific objectives

Geophysical Research Abstract

Our evolving understanding of aeolian bedforms, based on observation of dunes on different worlds

Dunes, dune fields, and ripples are unique and useful records of the interaction between wind and granular materials – finding such features on a planetary surface immediately suggests certain information about climate and surface conditions (at least during the dunes’ formation and evolution). Additionally, studies of dune characteristics under non-Earth conditions allow for “tests” of aeolian process models based primarily on observations of terrestrial features and dynamics, and refinement of the models to include consideration of a wider range of environmental and planetary conditions. To-date, the planetary aeolian community has found and studied dune fields on Mars, Venus, and the Saturnian moon Titan. Additionally, we have observed candidate “aeolian bedforms” on Comet 67P/Churyumov-Gerasimenko, the Jovian moon Io, and – most recently – Pluto. In this paper, we hypothesize that the progression of investigations of aeolian bedforms and processes on a particular planetary body follows a consistent sequence – primarily set by the acquisition of data of particular types and resolutions, and by the maturation of knowledge about that planetary body. We define that sequence of generated knowledge and new questions (within seven investigation phases) and discuss examples from all of the studied bodies. The aim of such a sequence is to better define our past and current state of understanding about the aeolian bedforms of a particular body, to highlight the related assumptions that require re-analysis with data acquired during later investigations, and to use lessons learned from planetary and terrestrial aeolian studies to predict what types of investigations could be most fruitful in the future

An Extremely Elongated Cloud over Arsia Mons Volcano on Mars: I. Life Cycle

We report a previously unnoticed annually repeating phenomenon consisting of the daily formation of an extremely elongated cloud extending as far as 1800 km westward from Arsia Mons. It takes place in the Solar Longitude (Ls) range of ~220-320, around the Southern solstice. We study this Arsia Mons Elongated Cloud (AMEC) using images from different orbiters, including ESA Mars Express, NASA MAVEN, Viking 2, MRO, and ISRO Mars Orbiter Mission (MOM). We study the AMEC in detail in Martian Year (MY) 34 in terms of Local Time and Ls and find that it exhibits a very rapid daily cycle: the cloud growth starts before sunrise on the western slope of the volcano, followed by a westward expansion that lasts 2.5 hours with a velocity of around 170 m/s in the mesosphere (~45 km over the areoid). The cloud formation then ceases, it detaches from its formation point, and continues moving westward until it evaporates before the afternoon, when most sun-synchronous orbiters observe. Moreover we comparatively study observations from different years (i.e. MYs 29-34) in search of interannual variations and find that in MY33 the cloud exhibits lower activity, whilst in MY34 the beginning of its formation was delayed compared to other years, most likely due to the Global Dust Storm. This phenomenon takes place in a season known for the general lack of clouds on Mars. In this paper we focus on observations, and a theoretical interpretation will be the subject of a separate paper

Quantitative analysis by renormalized entropy of invasive electroencephalograph recordings in focal epilepsy

Invasive electroencephalograph (EEG) recordings of ten patients suffering from focal epilepsy were analyzed using the method of renormalized entropy. Introduced as a complexity measure for the different regimes of a dynamical system, the feature was tested here for its spatio-temporal behavior in epileptic seizures. In all patients a decrease of renormalized entropy within the ictal phase of seizure was found. Furthermore, the strength of this decrease is monotonically related to the distance of the recording location to the focus. The results suggest that the method of renormalized entropy is a useful procedure for clinical applications like seizure detection and localization of epileptic foci.Comment: 10 pages, 5 figure

The dune effect on sand-transporting winds on Mars

Wind on Mars is a significant agent of contemporary surface change, yet the absence of in situ meteorological data hampers the understanding of surface–atmospheric interactions. Airflow models at length scales relevant to landform size now enable examination of conditions that might activate even small-scale bedforms (ripples) under certain contemporary wind regimes. Ripples have the potential to be used as modern ‘wind vanes’ on Mars. Here we use 3D airflow modelling to demonstrate that local dune topography exerts a strong influence on wind speed and direction and that ripple movement likely reflects steered wind direction for certain dune ridge shapes. The poor correlation of dune orientation with effective sand-transporting winds suggests that large dunes may not be mobile under modelled wind scenarios. This work highlights the need to first model winds at high resolution before inferring regional wind patterns from ripple movement or dune orientations on the surface of Mars today

Detecting and Characterising atmospheric gravity waves on Mars' atmosphere - Final results using data from OMEGA/Mars Express

We present the final results from the detection and characterisation of mesoscale waves on the lower clouds of Mars [1] using images from the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) [2] onboard the European Mars Express (MEx) space mission [3]. We used image navigation and processing techniques based on contrast enhancement and geometrical projections to characterise morphological properties of the detected gravity waves (GW), such as horizontal wavelength or packet length. Our study covers 25 months of data spanning from Jan. 2004 to Jan. 2006, and from June to July 2007, corresponding to a one Martian year [MY26- MY27]. Out of 148 detected wave packets, we were able to characterise 61 across more than 4000 images covering a broad region of the Martian globe. Our results reveal that waves exhibit an average horizontal wavelength of 23 km, which is consistent with previous observations [4,5]. We also extend the study by characterising their packet width, length and orientation. Taking advantage of the large dataset available from the OMEGA instrument, we also conducted a spatial and temporal investigation of the waves, namely their occurrence in specific local times and solar longitudes. Our characterisation showed a higher frequency of GW during daytime hours, particularly within the 13-15 LTST range. Concerning the solar longitude that is a measure of the Martian seasons, we noted that GW activity is prevalent during the winter season in both hemispheres, suggesting a relationship between seasonal variations and gravity wave generation, which was previously mentioned in the literature [6–8]. We will also present the preliminary results of GW using the HRSC instrument