Evidence for deliquescence of perchlorate salts has been discovered in the Martian polar region while possible brine flows have been observed in the equatorial region. This appears to contradict the ...idea that bulk deliquescence is too slow to occur during the short periods of the Martian diurnal cycle during which conditions are favorable for it. We conduct laboratory experiments to study the formation of liquid brines at Mars environmental conditions. We find that when water vapor is the only source of water, bulk deliquescence of perchlorates is not rapid enough to occur during the short periods of the day during which the temperature is above the salts' eutectic value, and the humidity is above the salts' deliquescence value. However, when the salts are in contact with water ice, liquid brine forms in minutes, indicating that aqueous solutions could form temporarily where salts and ice coexist on the Martian surface and in the shallow subsurface.
Key Points
The formation of brines at Martian conditions was studied experimentally
Bulk deliquescence from water vapor is too slow to occur diurnally on Mars
Brines form in minutes when salts are placed in direct contact with ice
The blowing of sand by wind, known as saltation, ejects dust aerosols into the atmosphere, creates sand dunes, and erodes geological features. We present a comprehensive numerical model of steady ...state saltation (COMSALT) that, in contrast to most previous studies, can reproduce a wide range of measurements and can simulate saltation over mixed soils. COMSALT calculates the motion of saltating particles due to gravity, fluid drag, particle spin, fluid shear, and turbulence and explicitly accounts for the retardation of the wind due to drag from saltating particles. Furthermore, we included a novel physically based parameterization of the ejection of surface particles by impacting saltating particles which matches experimental results. COMSALT is the first numerical saltation model to reproduce measurements of the wind shear velocity at the impact threshold (i.e., the lowest shear velocity for which saltation is possible) and of the aerodynamic roughness length in saltation. It also reproduces a range of other saltation processes, including profiles of the wind speed and particle mass flux, and the size distribution of saltating particles. As such, COMSALT is the first physically based numerical model to reproduce such a wide range of experimental data. Since we use a minimum of empirical relations, COMSALT can be easily adapted to study saltation under a variety of physical conditions, such as saltation on other planets, saltation under water, and saltating snow.
Mineral dust aerosols are responsible for some of the largest sources of uncertainties in our current understanding of climate change. Here we show that a severe drought is having a significant ...impact in one of largest sources of mineral dust aerosols of the U.S., the Owens Lake area in California's southwest. Measurements of aerosol concentration (PM2.5 particle matter) in the Owens Lake salty playa show that the annual mean concentration of PM2.5 aerosol has been increasing steadily since the beginning of the current drought, with periods of high aerosol concentration increasing from 4 months in 2013 to 9 months in 2015. Interestingly, the PM2.5 aerosol concentration usually increases abruptly from less than ~0.05 mg/m
to ~0.25 mg/m
. This occurs when saltation events break salt crusts produced by the efflorescence of brine in the salty playa. The brine is produced by either rainfall or runoff water. Based on this observation, we hypothesize that there is an upper limit of ~0.25 mg/m
in the annual mean PM2.5 aerosols concentration in the Owens Lake basin that might limit the impact of mineral dust aerosols on climate. Indeed, the upper annual limit of ~0.25 mg/m
has been nearly reached during the current drought.
•Variations in opacity at MSL are up to 0.047 and match best with high altitude cloud.•Where formed, clouds have regular spacing and estimated wavelengths of 2.0 to 3.3km.•Lack of clouds suggests ...Gale is relatively dry; MSL experience suggests an icier early Phoenix mission.
We report on the first 360 sols (LS 150° to 5°), representing just over half a Martian year, of atmospheric monitoring movies acquired using the NavCam imager from the Mars Science Laboratory (MSL) Rover Curiosity. Such movies reveal faint clouds that are difficult to discern in single images. The data set acquired was divided into two different classifications depending upon the orientation and intent of the observation. Up to sol 360, 73 Zenith movies and 79 Supra-Horizon movies have been acquired and time-variable features could be discerned in 25 of each. The data set from MSL is compared to similar observations made by the Surface Stereo Imager (SSI) onboard the Phoenix Lander and suggests a much drier environment at Gale Crater (4.6°S) during this season than was observed in Green Valley (68.2°N) as would be expected based on latitude and the global water cycle. The optical depth of the variable component of clouds seen in images with features are up to 0.047±0.009 with a granularity to the features observed which averages 3.8°. MCS also observes clouds during the same period of comparable optical depth at 30 and 50km that would suggest a cloud spacing of 2.0 to 3.3km. Multiple motions visible in atmospheric movies support the presence of two distinct layers of clouds. At Gale Crater, these clouds are likely caused by atmospheric waves given the regular spacing of features observed in many Zenith movies and decreased spacing towards the horizon in sunset movies consistent with clouds forming at a constant elevation. Reanalysis of Phoenix data in the light of the NavCam equatorial dataset suggests that clouds may have been more frequent in the earlier portion of the Phoenix mission than was previously thought.
Safe landings are imperative to accomplish NASA’s Artemis goal to enable human exploration on the Moon, including sample collection missions. However, a process known as plume surface interaction ...(PSI) presents a significant hazard to lunar landings. PSI occurs when the engine exhaust of a lander interacts with the surface ejecting large amounts of regolith particles at high velocities that can interfere with the landing, disturb the surface, and damage hardware. To better understand PSI, the particle impact event (PIE) sensor is being developed to measure the kinetic energy and the flux of ejecta during landings, to quantify the potential damage, and to quantify the ejecta displaced. Multiple parameters were estimated to define the PIE instrument requirements. These estimates demonstrate that ejecta can travel at velocities of up to 800 m/s and impact the surrounding area with energies of up to 400 µJ. A significant amount of ejecta can be deposited several 10 s of meters away from the landing site, modifying the surface and causing dust-related challenges. The PIE sensor will be launched for the first time in an upcoming lunar lander. Then, PIE measurements will be used to improve PSI prediction capabilities and develop mitigation strategies to ensure safe landings.
The Joint Workshop on Induced Special Regions convened scientists and planetary protection experts to assess the potential of inducing special regions through lander or rover activity. An Induced ...Special Region is defined as a place where the presence of the spacecraft could induce water activity and temperature to be sufficiently high and persist for long enough to plausibly harbor life. The questions the workshop participants addressed were: (1) What is a safe stand-off distance, or formula to derive a safe distance, to a purported special region? (2) Questions about RTGs (Radioisotope Thermoelectric Generator), other heat sources, and their ability to induce special regions. (3) Is it possible to have an infected area on Mars that does not contaminate the rest of Mars? The workshop participants reached a general consensus addressing the posed questions, in summary: (1) While a spacecraft on the surface of Mars may not be able to explore a special region during the prime mission, the safe stand-off distance would decrease with time because the sterilizing environment, that is the martian surface would progressively clean the exposed surfaces. However, the analysis supporting such an exploration should ensure that the risk to exposing interior portions of the spacecraft (i.e., essentially unsterilized) to the martian surface is minimized. (2) An RTG at the surface of Mars would not create a Special Region but the short-term result depends on kinetics of melting, freezing, deliquescence, and desiccation. While a buried RTG could induce a Special Region, it would not pose a long-term contamination threat to Mars, with the possible exception of a migrating RTG in an icy deposit. (3) Induced Special Regions can allow microbial replication to occur (by definition), but such replication at the surface is unlikely to globally contaminate Mars. An induced subsurface Special Region would be isolated and microbial transport away from subsurface site is highly improbable.
Simple analytical models for the flow structure of dust devils in steady state, and a “thermophysical” scaling theory that explains how these flow structures are maintained are reviewed. Then, ...results from high-resolution numerical simulations are used to provide insights into the structure of dust-devil-like vortices and study the impact of surface roughness on them. The article concludes with an overview of the influence of lofted dust on the flow structure of dust devils and a discussion of open questions.
Airborne dust plays an active role in determining the thermal structure and chemical composition of the present-day atmosphere of Mars and possibly the planet’s climate evolution over time through ...radiative–convective and cloud microphysics processes. Thus, accurate measurements of the distribution and variability of dust are required. Observations from the Mars Global Surveyor/Thermal Emission Spectrometer Mars Mars Reconnaissance Orbiter/Mars Climate Sounder and Mars Express/Fourier Transform Spectrometer and the Curiosity Rover have limited capability to measure dust. We show that spacecraft occultation of the Martian atmosphere at far-infrared frequencies between 1 and 10 THz can provide the needed global and temporal data on atmospheric dust by providing co-located measurements of temperature and dust opacity from the top of the atmosphere all the way down to the surface. In addition, spacecraft occultation by a small-satellite constellation could provide global measurements of the development of dust storms.
The objective of the Phoenix mission is to determine if Mars' polar region can support life. Since liquid water is a basic ingredient for life, as we know it, an important goal of the mission is to ...determine if liquid water exists at the landing site. It is believed that a layer of Martian soil preserves ice by forming a barrier against high temperatures and sublimation, but that exposed ice sublimates without the formation of the liquid phase. Here we show possible independent physical and thermodynamical evidence that besides ice, liquid saline water exists in areas disturbed by the Phoenix Lander. Moreover, we show that the thermodynamics of freeze‐thaw cycles can lead to the formation of saline solutions with freezing temperatures lower than current summer ground temperatures on the Phoenix landing site on Mars' Arctic. Thus, we hypothesize that liquid saline water might occur where ground ice exists near the Martian surface. The ideas and results presented in this article provide significant new insights into the behavior of water on Mars.
A simple theory for atmospheric convection based on the heat engine framework that predicts the buoyancy, the vertical velocity and the fractional area covered by either dry or moist convection in a ...state of statistical equilibrium is presented.
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