During the first year of NASA's Mars 2020 mission, Perseverance rover has investigated the dark crater floor unit of Jezero crater and four samples of this unit have been collected. The focus of this paper is to assess the potential of these samples to calibrate the crater‐based Martian chronology. We first review the previous estimation of crater‐based model age of this unit. Then, we investigate the impact crater density distribution across the floor unit. It reveals that the crater density is heterogeneous from areas which have been exposed to the bombardment during the last 3 Ga to areas very recently exposed to bombardment. It suggests a complex history of exposure to impact cratering. We also display evidence of several remnants of deposits on the top of the dark floor unit across Jezero below which the dark floor unit may have been buried. We propose the following scenario of burying/exhumation: the dark floor unit would have been initially buried below a unit that was a few tens of meters thick. This unit then gradually eroded away due to Aeolian processes from the northeast to the west, resulting in uneven exposure to impact bombardment over 3 Ga. A cratering model reproducing this scenario confirms the feasibility of this hypothesis. Due to the complexity of its exposure history, the Jezero dark crater floor unit will require additional detailed analysis to understand how the Mars 2020 mission samples of the crater floor can be used to inform the Martian cratering chronology.

The rate of occurrence of High Frequency (HF) marsquakes, as recorded by InSight at Homestead Hollow, Elysium Planitia, increased after about L-S= 33 degrees, and ceased almost completely by L-S= 187 degrees, following an apparently seasonal variation with a peak rate near aphelion. We define seismic rate models based on the declination of the Sun, annual solar tides, and the annual CO2 cycle as measured by atmospheric pressure. Evaluation of Akaike weights and evidence ratios shows that the declination of the Sun is the most likely, and the CO2 cycle the least likely driver of this seismic activity, although the discrimination is weak, and the occurrence of a few events in August 2020 is in favor for a triggering by CO2 ice load. We also show that no periodicity related to Phobos' orbit is present in the HF event sequence. Event rate forecasts are presented to allow further discrimination of candidate mechanisms from future observations. (C) 2021 The Author(s). Published by Elsevier B.V.

On February 18, 2021 NASA's Perseverance rover landed in Jezero crater, located at the northwestern edge of the Isidis basin on Mars. The uppermost surface of the present‐day crater floor is dominated by a distinct geologic assemblage previously referred to as the dark‐toned floor. It consists of a smooth, dark‐toned unit overlying and variably covering light‐toned, roughly eroded deposits showing evidence of discrete layers. In this study, we investigated the stratigraphic relations between materials that comprise this assemblage, the main western delta deposit, as well as isolated mesas located east of the main delta body that potentially represent delta remnants. A more detailed classification and differentiation of crater floor units in Jezero and determination of their relative ages is vital for the understanding of the geologic evolution of the crater system, and determination of the potential timeline and environments of habitability. We have investigated unit contacts using topographic profiles and DEMs as well as the distribution of small craters and fractures on the youngest portions of the crater floor. Our results indicate that at least some of the deltaic deposition in Jezero postdates emplacement of the uppermost surface of the crater floor assemblage. The inferred age of the floor assemblage can therefore help to constrain the timing of the Jezero fluviolacustrine system, wherein at least some lake activity postdates the age of the uppermost crater floor. We present hypotheses that can be tested by Perseverance and can be used to advance our knowledge of the geologic evolution of the area.

TERRAINS FOR MARS SAMPLE RETURN. M.C. Deahn, M.M. Morris, C.L. Brooks, N.R. Williams, M.P., Golombek, F.J. Calef III, S. Do, A.K. Nicholas, Department of Geological Sciences, State University of New York College at Geneseo, Department of Earth, Environmental, and Planetary Sciences, Rice University, Department of Geology, University of Hawaii at Manoa, Jet Propulsion Laboratory, California Institute of Technology.

Spiga, T. Pierron, M. van Driel, D. Banfield, E. Hauber, M. Grott, N. Müller, C. Perrin, A. Jacob, A. Lucas, B. Knapmeyer-Endrun, C. Newman, M. P. Panning, R. C. Weber, F. J. Calef, M. Böse, S. Ceylan, C. Charalambous, J. Clinton, D. Giardini, A. Horleston, T. Kawamura, A. Khan, M. Lemmon, R. Lorenz, W. T. Pike, J.-R. Scholz, P. Lognonné, B. Banerdt; DLR, Rutherfordstr. 2, 12489 Berlin, Germany, martin.knapmeyer@dlr.de, 2 Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland, 3 Department of Earth, Environmental, and Planetary Sciences, Brown University, Campus Box 1846, Providence, RI 02912-1846, USA, 4 Laboratoire de Météorologie Dynamique / Institut Pierre Simon Laplace (LMD/IPSL), Sorbonne Université, Centre National de la Recherche Scientifique (CNRS), École Polytechnique, École Normale Supérieure, 5 Cornell University, Cornell Center for Astrophysics and Planetary Science, Ithaca, NY, 14853, USA, 6 Université de Paris, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France, 7 Bensberg Observatory, University of Cologne, Vinzenz-Pallotti-Str. 26, 51429 Bergisch Gladbach, Germany, 8 Aeolis Research, 333 N Dobson Road, Unit 5, Chandler AZ 85224-4412, USA, 9 Jet Propulsion Laboratory, California Institute of Technology; 4800 Oak Grove Dr., M/S 183-301, Pasadena, CA 91109, USA, 10 NASA MSFC, NSSTC Mail Code ST13, 320 Sparkman Drive, Huntsville, AL 35805, USA, 11 Department of Electrical and Electronic Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, United Kingdom, 12 School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK, 13 Max Planck Institute for Solar System Research, Justusvon-Liebig-Weg 3, 37077 Göttingen, Germany, Space Science Institute, 4765 Walnut Street, Suite B, Boulder, CO 80301, USA Johns Hopkins Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA

IMPLICATIONS FOR THE TIMING OF DEGRADATION. J. A. Grant, N. H. Warner, C. M. Weitz, M. P. Golombek, S. A. Wilson, M. Baker, E. Hauber, V. Ansan, C. Charalambous, N. Williams, F. Calef, M. E. Banks, T. Pike, A. DeMott, M. Kopp, and H. Lethcoe-Wilson, Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6 at Independence SW, Washington, DC, 20560 (grantj@si.edu), SUNY Geneseo, Dept. Geol. Sci., 1 College Circle, Geneseo, NY 14454, Planetary Science Institute, 1700 East Fort Lowell, Tucson, AZ, 85719, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, German Aerospace Center (DLR), Inst. Planetary Research, University of Nantes, Laboratory of Planetary and Geodynamics, Imperial College, London, Department of Electrical and Electronic Engineering, NASA Goddard Space Flight Center, Greenbelt, MD.

This study reports in-situ sedimentologic evidence of giant floods in Gale crater, Mars, during the Noachian Period. Features indicative of floods are a series of symmetrical, 10 m-high gravel ridges that occur in the Hummocky Plains Unit (HPU). Their regular spacing, internal sedimentary structures, and bedload transport of fragments as large as 20 cm suggest that these ridges are antidunes: a type of sedimentary structure that forms under very strong flows. Their 150 m wavelength indicates that the north-flowing water that deposited them was at least 24 m deep and had a minimum velocity of 10 m/s. Floods waned rapidly, eroding antidune crests, and re-deposited removed sediments as patches on the up-flow limbs and trough areas between these ridges forming the Striated Unit (SU). Each patch of the SU is 50–200 m wide and long and consists of 5–10 m of south-dipping layers. The strike and dip of the SU layers mimic the attitude of the flank of the antidune on which they were deposited. The most likely mechanism that generated flood waters of this magnitude on a planet whose present-day average temperature is − 60 °C was the sudden heat produced by a large impact. The event vaporized frozen reservoirs of water and injected large amounts of CO 2 and CH 4 from their solid phases into the atmosphere. It temporarily interrupted a cold and dry climate and generated a warm and wet period. Torrential rainfall occurred planetwide some of which entered Gale crater and combined with water roaring down from Mt. Sharp to cause gigantic flash floods that deposited the SU and the HPU on Aeolis Palus. The warm and wet climate persisted even after the flooding ended, but its duration cannot be determined by our study.

The Mars Science Laboratory (MSL) Curiosity rover explored Vera Rubin ridge (VRR) in Gale crater, Mars, for almost 500 sols (Mars days) between arriving at the ridge on sol 1809 of the mission in September 2017 and leaving it on sol 2302 upon entering the Glen Torridon area south of the ridge. VRR is a topographic ridge on the central mound, Aeolis Mons (Mt. Sharp), in Gale crater that displays a strong hematite spectral signature from orbit. In-situ observations on the ridge led to the recognition that the ridge-forming rocks belong to the Murray formation, the lowermost exposed stratigraphic unit of the Mt. Sharp group, that was first encountered at the Pahrump Hills location. Including VRR rocks, the Murray formation, interpreted to be primarily deposited in an ancient lacustrine environment in Gale crater, is more than 300 m thick. VRR itself is composed of two stratigraphic members within the Murray formation, the Pettegrove Point member overlain by the Jura member. The Pettegrove Point member overlies the Blunts Point member of the Murray formation. Areas of gray coloration are observed in the Jura member predominantly, but also in the Pettegrove Point member. Generally, gray areas are found in local topographic depressions, but contacts between red and gray rocks crosscut stratigraphy. Additionally, cm-scale dark concretions with very high iron-content are commonly observed in gray rocks, typically surrounded by a lighttoned zone that is conversely depleted in iron. A key goal for the VRR campaign was to characterize geochemical variations in the ridge-forming rocks to investigate the role of primary and diagenetic controls on the geochemistry and morphology of VRR. Here, we present observations by the ChemCam instrument on VRR and compare these to the full Murray formation chemostratigraphy. This work was recently submitted to a special issue of JGRPlanets that detail the full VRR campaign.

DEGRADATION HISTORY OF HOMESTEAD HOLLOW. S. A. Wilson1, N. H. Warner2, J. A. Grant1, M. P. Golombek3, A. DeMott2, M. Kopp2, L. Berger3, C. M. Weitz4, E. Hauber5, V. Ansan6, C. Charalambous7, N. Williams3, F. Calef4, T. Pike7, H. Lethcoe3, and R. Hausmann3, 1Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6th at Independence SW, Washington, DC, 20560 (wilsons@si.edu), 2SUNY Geneseo, Department of Geological Sciences, 1 College Circle, Geneseo, NY 14454, 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 4Planetary Science Institute, 1700 East Fort Lowell, Tucson, AZ, 85719, 5German Aerospace Center (DLR), Institute of Planetary Research, 6University of Nantes, Laboratory of Planetary and Geodynamics, 7Imperial College, London, Department of Electrical and Electronic Engineering.

PROCESSES. V. Ansan, E. Hauber, M. Golombek, N. Warner, J. Grant, J. Maki, R. Deen, F. Calef, C. Weitz, J. Garvin, S. Wilson, N. Williams, C. Charalambous, T. Pike, H. Lethcoe, M. Kopp, A. De Mott, S. Smrekar, B. Banerdt, and R. Lorenz LPG-UMR CNRS 6112, University of Nantes, 2 rue de la houssinière, BP 92208, 44322 Nantes Cedex 3, France (veronique.ansan@univ-nantes.fr), German Aerospace Center (DLR), Institute of Planetary Research, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, SUNY Geneseo, Department of Geological Sciences, Smithsonian National Air and Space Museum, Center for Earth and Planetary Studies, Planetary Science Institute, Imperial College, London, Department of Electrical and Electronic Engineering, Johns Hopkins University Applied Physics Lab, Laurel, MD.

diagenesis in Vera Rubin ridge bedrock as implied by ChemCam observations. J. Frydenvang1 (jfrydenvang@ign.ku.dk), N. Mangold2, R.C. Wiens3, A.A. Fraeman4, L.A. Edgar5, C.M. Fedo6, J. L’Haridon2, C.C. Bedford7, S. Gupta8, J.P. Grotzinger9, J. Bridges10, B.C. Clark11, E.B. Rampe12, O. Forni13, P.J. Gasda3, N.L. Lanza3, A.M. Ollila3, P.-Y. Meslin13, V. Payré14, F. Calef4, M. Salvatore15, C. House16. 1University of Copenhagen, Copenhagen, Denmark; 2LPG, Univ. de Nantes; 3Los Alamos National Laboratory; 4Jet Propulsion Laboratory; 5USGS Flagstaff; 6Univ. of Tennessee; 7Open Univ.; 8Imperial College; 9Caltech; 10Univ. of Leicester; 11Space Science Institute; 12NASA Johnson Space Center; 13l'Institut de Recherche en Astrophysique et Planétologie; 14Rice Univ.; 15Northern Arizona Univ.; 16Penn State University.

By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars’ surface the SEIS (Seismic Experiment for Internal Structure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01 Hz to 50 Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1 sps and a continuous compound VBB/SP vertical axis at 10 sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking’s Mars seismic monitoring by a factor of \(\sim 2500\) at 1 Hz and \(\sim 200\,000\) at 0.1 Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars’ surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of \(M_{{w}} \sim 3\) at \(40^{\circ}\) epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution.