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To understand Martian palaeoclimatic conditions and the role of volatiles therein, the spatiotemporal evolution of gullies must be deciphered. While the spatial distribution of gullies has been extensively studied, their temporal evolution is poorly understood. We show that gully size is similar in very young and old craters. Gullies on the walls of very young impact craters (less than a few myr) typically cut into bedrock and are free of latitude-dependent mantle (LDM) and glacial deposits, while such deposits become increasingly evident in older craters. These observations suggest that gullies go through obliquity-driven degradationtextendashaccumulation cycles over time, controlled by: (1) LDM emplacement and degradation; and (2) glacial emplacement and removal. In glacially-influenced craters, the distribution of gullies on crater walls coincides with the extent of glacial deposits, which suggests that the melting of snow and ice played a role in the formation of these gullies. Yet, present-day activity is observed in some gullies on formerly glaciated crater walls. Moreover, in very young craters, extensive gullies have formed in the absence of LDM and glacial deposits, showing that gully formation can also be unrelated to these deposits. The Martian climate varied substantially over time, and the gully-forming mechanisms are likely to have varied accordingly.

The Mars Utah Rover Field Investigation “MURFI 2016” is a Mars Rover field analogue mission run by the UK Space Agency (UKSA) in collaboration with the Canadian Space Agency (CSA). MURFI 2016 took place between 22nd October and 13th November 2016 and consisted of a field team including an instrumented Rover platform, at the field site near Hanksville (Utah, USA), and an ‘Operations Team’ based in the Mission Control Centre (MOC) at the Harwell Campus near Oxford in the UK. The field site was chosen based on the collaboration with the CSA and its Mars-like local geology. It was used by the CSA in 2015 for Mars Rover trials, and in 2016, several teams used the site, each with their own designated working areas. The two main aims of MURFI 2016 were (i) to develop logistical and leadership experience in running field trials within the UKSA, and (ii) to provide members of the Mars Science community with Rover Operations experience, and hence to build expertise that could be used in the 2020 ExoMars Rover mission, or other future Rover missions. Because MURFI 2016 was the first solely UKSA-led Rover analogue trial, the most important objective was to learn how to best implement Rover trials in general. This included aspects of planning, logistics, field safety, MOC setup and support, communications, person management and science team development. Some aspects were based on past experience from previous trials but the focus was on ‘learning through experience’ - especially in terms of the Operations Team, who each took on a variety of roles during the mission.

Viscous flow features (VFFs) in Mars' mid latitudes are analogous to debris-covered glaciers on Earth. They have complex, often curvilinear patterns on their surfaces, which probably record histories of ice flow. As is the case for glaciers on Earth, patterns on the surfaces of VFFs are likely to reflect complexities in their subsurface structure. Until now, orbital observations of VFF-internal structures have remained elusive. We present observations of internal structures within a small, kilometer-scale VFF in the Nereidum Montes region of Mars' southern mid latitudes, using images from the Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) instruments on Mars Reconnaissance Orbiter. The VFF-internal structures are revealed by a gully incision, which extends from the VFF headwall to its terminus and intersects curvilinear undulations and a crevasse field on the VFF surface. Near to the VFF terminus, the curvilinear VFF-surface undulations connect to the VFF-internal layers, which are inclined and extend down to the VFF's deep interior, and possibly all the way to the bed. Similar structures are common near to the termini of glaciers on Earth; they form under ice flow compression where ice thins and slows approaching the ice margin, and ice flow is forced up towards the surface. We performed 3D ice flow modeling which supports this analogy, revealing that the inclined VFF-internal structures, and associated curvilinear structures on the VFF surface, are located in a zone of strong ice flow compression where ice flow deviates upwards away from the bed. The inclined VFF-internal structures we observe could represent up-warped VFF-internal layering transported up to the surface from the VFF's deep interior, or thrust structures representing debris transport pathways between the VFF's bed and its surface. Our observations raise numerous considerations for future surface missions targeting Mars' mid-latitude subsurface ice deposits. Inclined la

Bright radar reflections observed in the Ultimi Scopuli region of Mars’ south polar layered deposits1,2,3 by the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument have been interpreted as the signature of areas of subglacial water beneath it. However, other studies put forward alternative explanations, which do not imply the presence of liquid water4,5,6. Here we shed light on the issue by looking at the surface topography of the region. On Earth, reduced or absent basal friction, and consequent ice velocity changes, cause a distinct topographic signature over subglacial lakes7. Using Mars Orbiter Laser Altimeter data8, we identify and characterize an anomaly in the surface topography of the south polar layered deposits overlying the area of the putative lakes, similar to those found above terrestrial subglacial lakes of similar size. Ice flow model results suggest that comparable topographic anomalies form within 0.5–1.5 Myr with locally elevated geothermal heating9 or 2–5 Myr without elevated geothermal heating2. These findings offer independent support for the presence of basal water beneath Ultimi Scopuli and suggest that surface topography could supplement radar returns to help identify other potential subglacial water bodies.

The Mars Utah Rover Field Investigation “MURFI 2016” is a Mars Rover field analogue mission run by the UK Space Agency (UKSA) in collaboration with the Canadian Space Agency (CSA). MURFI 2016 took place between 22nd October and 13th November 2016 and consisted of a field team including an instrumented Rover platform, at the field site near Hanksville (Utah, USA), and an ‘Operations Team’ based in the Mission Control Centre (MOC) at the Harwell Campus near Oxford in the UK. The field site was chosen based on the collaboration with the CSA and its Mars-like local geology. It was used by the CSA in 2015 for Mars Rover trials, and in 2016, several teams used the site, each with their own designated working areas. The two main aims of MURFI 2016 were (i) to develop logistical and leadership experience in running field trials within the UKSA, and (ii) to provide members of the Mars Science community with Rover Operations experience, and hence to build expertise that could be used in the 2020 ExoMars Rover mission, or other future Rover missions. Because MURFI 2016 was the first solely UKSA-led Rover analogue trial, the most important objective was to learn how to best implement Rover trials in general. This included aspects of planning, logistics, field safety, MOC setup and support, communications, person management and science team development. Some aspects were based on past experience from previous trials but the focus was on ‘learning through experience’ - especially in terms of the Operations Team, who each took on a variety of roles during the mission.

The 2016 Mars Utah Rover Field Investigation (MURFI) was a Mars rover field trial run by the UK Space Agency in association with the Canadian Space Agency's 2015/2016 Mars Sample Return Analogue Deployment mission. MURFI had over 50 participants from 15 different institutions around the UK and abroad. The objectives of MURFI were to develop experience and leadership within the UK in running future rover field trials; to prepare the UK planetary community for involvement in the European Space Agency/Roscosmos ExoMars 2020 rover mission; and to assess how ExoMars operations may differ from previous rover missions. Hence, the wider MURFI trial included a ten-day (or ten-‘sol’) ExoMars rover-like simulation. This comprised an operations team and control centre in the UK, and a rover platform in Utah, equipped with instruments to emulate the ExoMars rovers remote sensing and analytical suite. The operations team operated in ‘blind mode’, where the only available data came from the rover instruments, and daily tactical planning was performed under strict time constraints to simulate real communications windows. The designated science goal of the MURFI ExoMars rover-like simulation was to locate in-situ bedrock, at a site suitable for sub-surface core-sampling, in order to detect signs of ancient life. Prior to “landing”, the only information available to the operations team were Mars-equivalent satellite remote sensing data, which were used for both geologic and hazard (e.g., slopes, loose soil) characterisation of the area. During each sol of the mission, the operations team sent driving instructions and imaging/analysis targeting commands, which were then enacted by the field team and rover-controllers in Utah. During the ten-sol mission, the rover drove over 100 m and obtained hundreds of images and supporting observations, allowing the operations team to build up geologic hypotheses for the local area and select possible drilling locations. On sol 9, the team obtained