20-EPN2-121: Constraining the movement of groundwater and fluid expulsion within playa environments on Mars

20-EPN2-121: Constraining the movement of groundwater and fluid expulsion within playa environments on Mars

Visit by Gene Schmidt, Università degli Studi Roma Tre (Italy) and Erica Luzzi, Jacobs University (Germany) to TA1.5 Makgadikgadi Salt Pans (Botswana).
Dates of visit: 20-27 October 2021

Across the surface of Mars there is evidence of past lacustrine and evaporitic environments found within basins and craters, where often layered sedimentary deposits and hydrated minerals are observed. However, the intensity, duration and precise phases of water cycle activity during this period remain unresolved. Although several geological processes and locations on Earth have been previously proposed as examples to describe these deposits on Mars, we lack a strong visualisation of what water activity might have looked like during evaportic stages within basins and craters. The Makgadikgadi Salt Pans of Botswana, where once the Makgadikgadi Lake existed, is a present evaporitic environment rich in hydrated minerals and water activity. It is a depression located at the southwestern end of a northeast-southwest set of graben. Faults have been previously proposed to have been pathways for groundwater to enter basins and craters on Mars, which then contributed to both the deposition and alteration of the sedimentary deposits. Thus, imaging the subsurface of a similar environment on Earth can help us to better understand how water processes on Mars might have continued as the Martian global climate became drier.

By using the already established locations of the faults to the north of the pans, we used remote sensing techniques to trace the best location of the faults underneath the pans (Figures 1 and 2). We then used electrical resistivity surveys to image 70 – 150 m of the pans’ subsurface where the faults were deemed most likely to occur. This work allows us to better understand the possibilities of what the underlying lithology of rocks within filled basins and craters might look like. Furthermore, it demonstrates the scientific importance of future missions to employ subsurface imaging techniques on Mars.

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Dust Devil Diary

Dust Devil Diary

From 29 September – 6 October 2021, researchers Daniel Toledo and Victor Apestigue (Instituto Nacional de Técnica Aeroespacial (INTA), Spain) were funded by the Europlanet 2024 Research Infrastructure (RI) Transnational Access (TA) programme to visit the Makgadikgadi Salt Pans in Botsawana. The trip was led by Fulvio Franchi (Botswana International University of Science and Technology (BIUST)) who is responsible for the Botswana Planetary Field Analogue for Europlanet 2024 RI. Ignacio Arruego, Javier Martinez-Oter and Felipe Serrano (INTA) also participated in the field trip. In this guest post, Daniel Toledo reports on the field trip.

The main goal of the field campaign in the Makgadikgadi Salts Pans was to study how dust is lifted into the air. For our investigation, we used the spare units of the Radiation and Dust Sensor (RDS) from the NASA Mars 2020 mission and the Sun Irradiance Sensor (SIS) from the ExoMars 2022 mission (see Figure 1), which are designed to study dust carried in the atmosphere of Mars by measuring how sunlight is scattered by the dust particles.

In addition to giving information about the properties of airbourne dust, these instruments are also sensitive to the presence of dust devils – swirling columns of sand and dust that are a common feature of desert areas on Mars and on Earth. RDS and SIS can detect the changes over time in the sky brightness produced by a dust devil, and this offers a unique opportunity for monitoring and studying such events during the Mars 2020 and ExoMars 2022 missions. However, to be able to characterise and interpret dust devil observations on Mars, we first need to understand how dust devils affect SIS and RDS signals by thorough testing and evaluation of the instruments in Mars-like conditions on Earth. 

Figure 1. (Left) RDS instrument: two sets of eight photodiodes. One set is pointed upward, with each photodiode covering a different wavelength range between 250-1000 nanometres. The other set is pointed sideways, 20° above the horizon, and they are spaced 45° degrees apart in azimuth to sample all directions at a single wavelength; a zenith-pointed camera (Skycam) with special optics is designed to measure column optical depth.(Right) SIS instrument: Five detectors pointed at zenith and with different spectral bands and Fields of View (FOVs); twelve lateral detectors (six in the ultraviolet range and six in the near infrared range) pointed sideways; a micro-spectrometer pointed directly upwards (at zenith) with a spectral resolution of 10 nanometres in the 340-780 nanometres range. 
Figure 2. Dust devils observed in Makgadikgadi Salt Pans (left panel) and on Mars (right panel). A typical dust devil on Mars spans from hundreds of metres to thousands of metres in diameter, with a height one-eight times as large. Dust devils of Mars are thought to account for the ~50% of the total dust budget, and they represent continuous source of lifted dust, active even outside the dust storms season. For these reasons, they have been proposed as the main mechanism able to sustain the constantly-observed dust haze in the martian atmosphere.

To achieve this goal, we planned a field campaign from 29 September to 6 October in the southern part of Makgadikgadi Salt Pans (see Figure 3), in the Pan near Mopipi town. This location is characterised by frequent dust devil events and conditions that promote the lifting of high levels of aerosols (dust and particles) into the atmosphere.

Each day of the campaign, we set up RDS and SIS at two different locations from sunrise to sunset, separated by about 25 m, along with:

  1. Two cameras to record panoramic videos during the campaign period.
  2. A Vaisala weather station to perform measurements of pressure, wind direction and intensity, temperature and relative humidity.
  3. A ZEN radiometer to measure how much light was absorbed by the dust at different wavelengths.

The objective of having the two main instruments at two different locations was observe the dust lifting events from different perspectives.

During the campaign, we observed a large number of dust devils (many more than 10) and dust lifting events produced by wind gusts (over 10). For each dust lifting, we recorded the dust devil distance, the size, duration and direction. To do this, we marked out concentric circles with radii of 25, 50, 75, 100, 125 and 150 m on the ground. This information along with the videos made by the cameras, helped us to establish the amount of dust lifted by the dust devil as well as their distances from the instruments. All the data collected for each event was key to establish the RDS and SIS capabilities for dust lifting characterisation on Mars.

The first two days of the campaign were characterised by high dust-loading conditions and frequent formations of dust lifting events produced by dust devils or wind gusts. During these two days, each dust lifting event registered by the cameras was also detected by RDS and SIS, with signals showing a sharp peak at the time when the event passed within the sensors field of view. Preliminary analysis suggests that we can infer from RDS and SIS signals the difference between dust lifting events produced by dust devils and those produced by wind gusts – an important result for the observations on Mars.

Makgadikgadi Salt Pans. Credit: Google
Figure 3. Map indicating the location selected for carrying out the field campaign in the southern part of Makgadikgadi Salt Pans (red square) and the village Rakops (black square) where different lodges are available.

The third day of campaign had to be cancelled due to rain. This resulted in a lower dust-loading conditions in the following days, and thus the amount of dust lifted by vortices or wind gusts was smaller compared to the first two days. 

Upon return to BIUST in Palapye on 6 October, we held a seminar for staff and students titled Atmospheric science on Mars: from Earth analogues to future planetary networks.

In summary, the campaign was a complete success. Our observations have demonstrated the capability of the RDS and SIS sensors to detect and characterise dust devils on Mars. The analysis of the signals along with the information acquired by the other instruments will allow us to quantitatively establish the sensors limit of detection. In addition, the rainy episode offered us the chance to study dust lifting events in different aerosol loading conditions.

Makgadikgadi Salt Pans TA Field Trip, 29 September - 7 October (Spanish Trip - Daniel Toledo)

20-EPN2-065Characterizing dust lifting events using the ground-based Mars-2020-RDS and ExoMars-2022-SIS radiometers. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149.

20-EPN2-065: Characterising dust lifting events using ground-based Mars-2020 and ExoMars radiometers

20-EPN2-046: Characterising dust lifting events using the ground-based Mars-2020-RDS and ExoMars-2022-SIS radiometers

Visit by Daniel Toledo, INTA (Spain) to TA1.5 AU Makgadikgadi Salt Pans (Botswana).
Dates of visit: 29 September – 06 October 2021

Report Summary:

On Mars, the airborne dust is a critical factor that drives the weather and climate of the planet. Dust devils are thought to account for the ~50 % of the total dust budget, and they represent a continuous source of dust, present even outside the dust storms period. For these reasons they have been proposed as the main mechanism able to sustain the observed dust haze of the martian atmosphere. However, additional dust devil surveys covering long diurnal periods are needed to place quantitative constraints on the cycles of these events. In this regard, the present and future observations of the Radiation and Dust Sensor (RDS) and the Sun Irradiance Sensor (SIS), which are part of NASA Mars 2020 and ESA/Roscosmos ExoMars 2022 missions, offer a unique opportunity to monitoring dust devils at high temporal resolution from sunrise to sunset, and with an excellent spatial coverage.

The main goal of the field campaign in the Makgadikgadi Salts Pans (20-EPN2-065) was to study dust lifting events using the spare units of RDS and SIS. During the campaign (29 Sept to 6 Oct 2021), a large number of dust devils (>10) and dust lifting events produced by wind gusts (>10) were observed by RDS and SIS sensors. For each case, information on distance, size, temporal duration and direction was registered. This information along with observations made by other instruments (e.g. wind speed and direction), have allowed us to study the potential RDS and SIS capabilities for dust lifting characterisation on Mars.

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