Mineral dust particles represent the most abundant component of atmospheric aerosol in terms of dry mass. They play a key role in climate and climate change, so the study of their emission processes ...is of utmost importance. Measurements of dust emission into the atmosphere are scarce, so that the dust load is generally estimated using models. It is known that the emission process can generate strong atmospheric electric fields. Starting from the data we acquired in the Sahara desert, here, we show for the first time that depending on the relative humidity conditions, electric fields contribute to increase up to a factor of 10 the amount of particles emitted into the atmosphere. This means that electrical forces and humidity are critical quantities in the dust emission process and should be taken into account in climate and circulation models to obtain more realistic estimations of the dust load in the atmosphere.
Key Points
The tight interrelation between the dust‐lifting process and atmospheric electric field is shown
The role of the relative humidity is demonstrated
Electric forces contribute to the entrainment of dust in the atmosphere
Martian dunes are sculpted by meter‐scale bed forms, which have been interpreted as wind ripples based on orbital data. Because aeolian ripples tend to orient and migrate transversely to the last ...sand‐moving wind, they have been widely used as wind vanes on Earth and Mars. In this report we show that Martian large ripples are dynamically different from Earth's ripples. By remotely monitoring their evolution within the Mars Science Laboratory landing site, we show that these bed forms evolve longitudinally with minimal lateral migration in a time‐span of ~ six terrestrial years. Our observations suggest that the large Martian ripples can record more than one wind direction and that in certain cases they are more similar to linear dunes from a dynamic point of view. Consequently, the assumption of the transverse nature of the large Martian ripples must be used with caution when using these features to derive wind directions.
Key Points
Martian large ripples dynamics are more similar to longitudinal dunes than impact ripples
First evidence for longitudinal large ripple migration on Mars
Martian large ripples consistently migrate in Gale Crater
Aeolian landforms are widespread in our solar system. Understanding the exact nature and processes of formation of these features are challenging tasks necessitating a strong collaboration between ...scientists with different skills and scientific backgrounds. This paper describes the special issue for the 5th International Planetary Dunes Workshop, which includes 15 research papers and three commentaries. Among the 18 papers included in this collection, 16 cover Martian aeolian science and two Titan aeolian science. The papers presented focus on bedform morphology and dynamics via remote sensing data, modeling, analogs studies and laboratory experiments. Here we put the main results of the papers in their appropriate scientific context and discuss potential future lines of research.
Plain Language Summary
Wind‐sculpted (aeolian) landforms are found on many bodies of our solar system. Their study is fundamental to understanding the geology and climate of these bodies and to safely plan extraterrestrial missions. Here we introduce a collection of papers describing aeolian features on Mars and Titan. Collectively, the papers presented in this special issue show the importance of an interdisciplinary approach in comprehending what we are seeing on other planets. The study of wind landforms in extraterrestrial planets is sparking a new interest on terrestrial aeolian geomorphology highlighting the significance of planetary studies in advancing the understanding of our Earth.
Key Points
Results from the 5th International Planetary Dunes Workshop are presented
Study of aeolian landforms can shed light on climatic changes and are key for landing site characterization
Combined use of imaging and high‐resolution flow modeling can provide new insights into the mechanism and processes that form bedforms
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.
Plain Language Summary
Oxia Planum on Mars is the landing site for the ExoMars 2022 mission. The region likely hosted a standing body of water, but the effect of the wind was also important in shaping the landscape. In this study, we first describe a set of linear ridges that, in our interpretation, were sculpted by the wind in a more recent past. We also show that the wind that formed the ridges (Periodic Bedrock Ridges) was blowing from a different direction than the ones that formed younger ripples on top, suggesting a complex geological history of wind erosion and deposition that will be further investigated during the ExoMars mission.
Key Points
We present the first evidence for a periodic bedrock ridge (PBRs) pattern from the ExoMars 2022 landing site
Formative paleowind directions are extrapolated from PBRs and transverse aeolian ridges
Evidence for an Amazonian change in the wind regime are provided
Megaripple Migration on Mars Silvestro, S.; Chojnacki, M.; Vaz, D. A. ...
Journal of geophysical research. Planets,
August 2020, Letnik:
125, Številka:
8
Journal Article
Recenzirano
Odprti dostop
Aeolian megaripples, with 5‐ to 50‐m spacing, are abundant on the surface of Mars. These features were repeatedly targeted by high‐resolution orbital images, but they have never been observed to ...move. Thus, aeolian megaripples (especially the bright‐toned ones often referred as Transverse Aeolian Ridges—TARs) have been interpreted as relict features of a past climate. In this report, we show evidence for the migration of bright‐toned megaripples spaced 1 to 35 m (5 m on average) in two equatorial areas on Mars indicating that megaripples and small TARs can be active today. The moving megaripples display sand fluxes that are 2 orders of magnitudes lower than the surrounding dunes on average and, unlike similar bedforms on Earth, can migrate obliquely and longitudinally. In addition, the active megaripples in the two study areas of Syrtis Major and Mawrth Vallis show very similar flux distributions, echoing the similarities between dune crest fluxes in the two study areas and suggesting the existence of a relationship between dune and megaripple fluxes that can be explored elsewhere. Active megaripples, together with high‐sand flux dunes, represent a key indicator of strong winds at the surface of Mars. A past climate with a denser atmosphere is not necessary to explain their accumulation and migration.
Plain Language Summary
Similar to what is found in deserts on Earth, the wind has accumulated sandy landforms (bedforms) on the Martian surface, such as dunes and ripples. Ripples on Earth are mostly spaced at ~10 cm, but a particular kind of ripples called “megaripples” can be 30 cm to tens of meters spaced. Megaripples have coarse sand grains (>1 mm) accumulated at their crests, so only strong winds can move them. Mars has a faint atmosphere, and according to computer models, winds able to mobilize coarse sand grains are not predicted to blow at the surface. Thus, Martian megaripples are often considered to be static relics of a past climate where the atmosphere was denser. Here we show the first evidence for the movement of bright megaripples on Mars showing that some of these bedforms can be active today and do not require past climatic states for their origin as has been assumed.
Key Points
Bright‐toned megaripple migration is identified on the surface of Mars for the first time
These features are similar to Transverse Aeolian Ridges, which had been assumed to be dormant under the current climate
Megaripple crest fluxes are, on average, 2 orders of magnitude lower than local dune crest fluxes
In this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in Nili Patera on Mars. The measured average migration of ∼1.7 meters in less than 4 ...terrestrial months clearly indicates that active sand saltation is occurring in the study area. In addition, we document widespread changes in the dune base‐ground surface contact and in the slip face structures, showing that not only the ripples, but the whole dunes are actually migrating in the present‐day atmospheric setting. These results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on Mars may also be active.
A multidisciplinary study of an ancient area of Mars (Early to Late Noachian) located in Arabia Terra is presented, centred at 6°1′N, 354°54′ E and including the 55 km size Vernal crater. By means ...of different spatial scale imagery datasets and digital terrain models (MOLA, THEMIS, HRSC, CTX, CaSSIS and HiRISE), we prepare a high-resolution geological map of the study site. We highlight the different bedrock stratigraphy inside the Vernal crater which is of particular exobiological interest given the presence of putative ancient hot springs, as well as identifying multiple transverse aeolian ridges, inverted fracture networks and paleochannels, mounds, and a 58 m fresh crater located just outside Vernal crater rim. Within all low-latitude regions of Mars, the studied site presents the highest values (up to 16.0 wt%) of water equivalent hydrogen, hence suggesting that there is a widespread presence of in situ subsurface (at maximum depths of 1–2 m) natural resources, such as water ice and/or hydrated minerals. The equatorial location of the area results in the maximum surface temperature and the highest mean solar flux gatherable on the surface of the planet throughout the year. The interesting scientific case, coupled with the presence of in situ exploitable resources and the thorough accomplishment of all landing/roving engineering safety requirements, make the Vernal crater area a strong landing site candidate for future human exploration of Mars.
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•ISRU and Human landing site candidate close to Mars equator.•First high-resolution geological map of Vernal crater and its surroundings.•Ancient hot springs exobiological potential.•In situ subsurface resource identification.•Engineering safety fulfilment and exploration zones characterization.
We present evidence of widespread aeolian activity in the Arabia Terra/Meridiani region (Mars), where different kinds of aeolian modifications have been detected and classified. Passing from the ...regional to the local scale, we describe one particular dune field in Meridiani Planum, where two ripple populations are distinguished by means of different migration rates. Moreover, a consistent change in the ripple pattern is accompanied by significant dune advancement (between 0.4–1 meter in one Martian year) that is locally triggered by large avalanche features. This suggests that dune advancement may be common throughout the Martian tropics.
Key Points
Active sand saltation is common on the Martian surface
Dune advancement and sand movement not related to CO2 frost sublimation
Different ripple populations are distinguished by means of different migration rates
An aeolian system located in Aonia Terra (eastern Thaumasia region) consists of six dark dune fields. The dune pattern suggests an organized extended sand transport system, which is characterized by ...the presence of long sand corridors. The latter connects the different ergs with potential sources. The sand stored in the ergs is provided by layered materials exposed in pits and crater walls and by the ergs themselves. Most of the sand converges from the marginal dune fields into the central erg C. The latter develops in an area of convergence of at least three different winds: from the southwest, the northeast and the northwest. The northwesterly flows seem to postdate the other winds as suggested by the development of a complex dune pattern in the western portion of the erg C, representing a successive episode of aeolian construction. Collectively such complex dune patterns show how dune fields could record major changes in the wind regimes of Mars.
The first in situ investigation of an active dune field on another planetary surface occurred in 2015–2016 when the Mars Science Laboratory Curiosity rover investigated the Bagnold Dunes on Mars. ...High Resolution Imaging Science Experiment images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra‐annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity. Curiosity surface images show that limited changes nevertheless occurred, with movement of large grains, particularly on freshly exposed surfaces, two occurrences of secondary grain flow on the slip face of Namib Dune, and a slump on a freshly exposed surface of a large ripple. These changes are seen at Martian solar day (sol)‐to‐sol time scales. Grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0.3–0.4 m s−1. Overall, the correlation between changes and peak Rover Environmental Monitoring Station (REMS) winds is moderate, with high wind events associated with changes in some cases, but not in others, suggesting that other factors are also at work. The distribution of REMS 1 Hz wind speeds shows a significant tail up to the current 20 m s−1 calibration limit, indicating that even higher speed winds occur. Nonaeolian triggering mechanisms are also possible. The low activity period at the dunes documented by Curiosity provides clues to processes that dominated in the Martian past under conditions of lower obliquity.
Plain Language Summary
The modification of Martian sand dunes and nearby areas by the wind is monitored from the surface by the Curiosity rover and from orbit by the High Resolution Imaging Science Experiment camera. When the rover was at the dunes, changes were small but still showed moving grains and slumps. The results indicate that surface changes occur even in low activity periods, providing insight into past Martian climates.
Key Points
Dune activity observed on the surface of Mars
Changes seen from Mars orbit and surface
First estimate of wind threshold speeds on Mars in situ
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