It has been known for decades that carbon dioxide (CO2) ice clouds exist in the Martian atmosphere. According to remote sensing observations and previous modeling studies, the Martian CO2 ice ...crystals may be sufficiently large to generate halos. However, observations of CO2 ice crystal halos have not been reported so far. This study simulates the scattering and polarized phase functions at a wavelength of 0.48 μm based on state‐of‐the‐art light‐scattering computational capabilities. The specific CO2 ice crystal habits considered in the simulations include cubes, octahedrons, cubo‐octahedrons, and truncated octahedrons of various sizes. The halos produced by CO2 ice crystals peak at approximately 29° and 42°. Moreover, large CO2 ice crystals may cause strong scattering peaks at 155° and 180°. An ensemble of water (H2O) ice crystals and CO2 ice crystals with appropriate mixing fractions might be responsible for a halo occurrence recently observed on Mars.
Plain Language Summary
On Earth, optical phenomena, particularly halos, glories, and rainbows, caused by ice crystals and water droplets, are often observed in the sky. In the Martian atmosphere consisting of approximately 95% carbon dioxide (CO2) by volume, CO2 ice crystals can exist and result in optical phenomena similar to those observed on Earth. In the present study, the optical properties of CO2 ice crystals are computed to explain halos and other optical features caused by these particles. Because the habits (shapes) of CO2 ice crystals are different from those of water droplets and ice crystals, the optical phenomena produced by the former have different positions in the sky compared to the counterparts caused by water droplets and ice crystals. Furthermore, a halo observed recently on Mars might be caused by a mixture of water ice crystals and CO2 ice crystals.
Key Points
CO2 ice crystals in the Martian atmosphere can produce halos at approximately 29° and 42°
Optical phenomena associated with light scattering by CO2 ice crystals can be used to estimate the particle habits and sizes
A halo observed on Mars might be caused by an ensemble of H2O and CO2 ice crystals
•Thermal inertia and albedo are derived from ground temperature measurements along the Curiosity rover's traverse.•Diffuse water ice clouds or hazes can significantly influence ground temperatures in ...the southern fall and winter.•The shape of the diurnal ground temperature curve is used to isolate the bedrock thermal inertia from other materials within the sensor footprint.•Thermal inertias of sedimentary rock may be significantly higher than apparent in data sets with sparse local time coverage.
The REMS instrument onboard the Mars Science Laboratory rover, Curiosity, has measured ground temperature nearly continuously at hourly intervals for two Mars years. Coverage of the entire diurnal cycle at 1Hz is available every few martian days. We compare these measurements with predictions of surface-atmosphere thermal models to derive the apparent thermal inertia and thermally derived albedo along the rover's traverse after accounting for the radiative effects of atmospheric water ice during fall and winter, as is necessary to match the measured seasonal trend. The REMS measurements can distinguish between active sand, other loose materials, mudstone, and sandstone based on their thermophysical properties. However, the apparent thermal inertias of bedrock-dominated surfaces (∼350–550Jm−2K−1s−½) are lower than expected. We use rover imagery and the detailed shape of the diurnal ground temperature curve to explore whether lateral or vertical heterogeneity in the surface materials within the sensor footprint might explain the low inertias. We find that the bedrock component of the surface can have a thermal inertia as high as 650–1700Jm−2K−1s−½ for mudstone sites and ∼700Jm−2K−1s−½ for sandstone sites in models runs that include lateral and vertical mixing. Although the results of our forward modeling approach may be non-unique, they demonstrate the potential to extract information about lateral and vertical variations in thermophysical properties from temporally resolved measurements of ground temperature.
•The derivation of the Mars Exploration Rover opacity record is described.•Dust aerosol size variations are characterized across seasons and storm events.•Clouds contribute to northern summer optical ...depth at the Opportunity site.•The dust significantly affects the energy balance and frequency of dust devils.
Dust aerosol plays a fundamental role in the behavior and evolution of the martian atmosphere. The first five Mars years of Mars Exploration Rover data provide an unprecedented record of the dust load at two sites. This record is useful for characterization of the atmosphere at the sites and as ground truth for orbital observations. Atmospheric extinction optical depths have been derived from solar images after calibration and correction for time-varying dust that has accumulated on the camera windows. The record includes local, regional, and globally extensive dust storms. Comparison with contemporaneous thermal infrared data suggests significant variation in the size of the dust aerosols, with a 1μm effective radius during northern summer and a 2μm effective radius at the onset of a dust lifting event. The solar longitude (LS) 20–136° period is also characterized by the presence of cirriform clouds at the Opportunity site, especially near LS=50° and 115°. In addition to water ice clouds, a water ice haze may also be present, and carbon dioxide clouds may be present early in the season. Variations in dust opacity are important to the energy balance of each site, and work with seasonal variations in insolation to control dust devil frequency at the Spirit site.
We used Phoenix Surface Stereo Imager data, constrained by other Phoenix and MRO data taken via a planned coordinated measurement campaign, along with radiative transfer modeling to assess the ...vertical water vapor profile at the Phoenix arctic location during its spring and summer mission. We examined 16 mid-afternoon observations spanning Ls = 97.5°–148°. We developed a 2-layer model of vapor distribution which reproduces the water vapor band depth. Using the results of the 2-layer model, we retrieved the mass mixing ratios in each layer and the implied surface vapor pressure. We found that near surface water vapor was enhanced relative to higher layers, resulting in a large percentage of the water column (>25% and up to nearly 100%) confined below ~2.5 km.
•Radiative transfer analysis of Phoenix images taken with a water vapor band is presented.•Water vapor is confined near the surface and not well mixed in the boundary layer.•Mechanisms for confining water vapor near the surface are suggested.
Mars methane detection and variability at Gale crater Webster, Christopher R.; Mahaffy, Paul R.; Atreya, Sushil K. ...
Science (American Association for the Advancement of Science),
01/2015, Volume:
347, Issue:
6220
Journal Article
Peer reviewed
Open access
Reports of plumes or patches of methane in the martian atmosphere that vary over monthly time scales have defied explanation to date. From in situ measurements made over a 20-month period by the ...tunable laser spectrometer of the Sample Analysis at Mars instrument suite on Curiosity at Gale crater, we report detection of background levels of atmospheric methane of mean value 0.69 ± 0.25 parts per billion by volume (ppbv) at the 95% confidence interval (CI). This abundance is lower than model estimates of ultraviolet degradation of accreted interplanetary dust particles or carbonaceous chondrite material. Additionally, in four sequential measurements spanning a 60-sol period (where 1 sol is a martian day), we observed elevated levels of methane of 7.2 ± 2.1 ppbv (95% CI), implying that Mars is episodically producing methane from an additional unknown source.
Atmospheric Science with InSight Spiga, Aymeric; Banfield, Don; Teanby, Nicholas A. ...
Space science reviews,
10/2018, Volume:
214, Issue:
7
Journal Article
Peer reviewed
Open access
In November 2018, for the first time a dedicated geophysical station, the InSight lander, will be deployed on the surface of Mars. Along with the two main geophysical packages, the Seismic Experiment ...for Interior Structure (SEIS) and the Heat-Flow and Physical Properties Package (HP
3
), the InSight lander holds a highly sensitive pressure sensor (PS) and the Temperature and Winds for InSight (TWINS) instrument, both of which (along with the InSight FluxGate (IFG) Magnetometer) form the Auxiliary Sensor Payload Suite (APSS). Associated with the RADiometer (RAD) instrument which will measure the surface brightness temperature, and the Instrument Deployment Camera (IDC) which will be used to quantify atmospheric opacity, this will make InSight capable to act as a meteorological station at the surface of Mars. While probing the internal structure of Mars is the primary scientific goal of the mission, atmospheric science remains a key science objective for InSight. InSight has the potential to provide a more continuous and higher-frequency record of pressure, air temperature and winds at the surface of Mars than previous
in situ
missions. In the paper, key results from multiscale meteorological modeling, from Global Climate Models to Large-Eddy Simulations, are described as a reference for future studies based on the InSight measurements during operations. We summarize the capabilities of InSight for atmospheric observations, from profiling during Entry, Descent and Landing to surface measurements (pressure, temperature, winds, angular momentum), and the plans for how InSight’s sensors will be used during operations, as well as possible synergies with orbital observations. In a dedicated section, we describe the seismic impact of atmospheric phenomena (from the point of view of both “noise” to be decorrelated from the seismic signal and “signal” to provide information on atmospheric processes). We discuss in this framework Planetary Boundary Layer turbulence, with a focus on convective vortices and dust devils, gravity waves (with idealized modeling), and large-scale circulations. Our paper also presents possible new, exploratory, studies with the InSight instrumentation: surface layer scaling and exploration of the Monin-Obukhov model, aeolian surface changes and saltation / lifing studies, and monitoring of secular pressure changes. The InSight mission will be instrumental in broadening the knowledge of the Martian atmosphere, with a unique set of measurements from the surface of Mars.
A primary objective of the Phoenix mission was to examine the characteristics of high latitude ground ice on Mars. We report observations of ground ice, its depth distribution and stability ...characteristics, and examine its origins and history. High latitude ground ice was explored through a dozen trench complexes and landing thruster pits, over a range of polygon morphological provinces. Shallow ground ice was found to be abundant under a layer of relatively loose ice‐free soil with a mean depth of 4.6 cm, which varied by more than 10x from trench to trench. These variations can be attributed mainly to slope effects and thermal inertia variations in the overburden soil affecting ground temperatures. The presence of ice at this depth is consistent with vapor‐diffusive equilibrium with respect to a mean atmospheric water content of 3.4 × 1019 m−3, consistent with the present‐day climate. Significant ice heterogeneity was observed, with two major forms: ice‐cemented soil and relatively pure light toned ice. Ice‐cemented soils, which comprised about 90% of the icy material exposed by trenching, are best explained as vapor deposited pore ice in a matrix supported porous soil. Light toned ice deposits represent a minority of the subsurface and are thought to consist of relatively thin near surface deposits. The origin of these relatively pure ice deposits appears most consistent with the formation of excess ice by soil ice segregation, such as would occur by thin film migration and the formation of ice lenses, needle ice, or similar ice structures.
Records of solar array currents recorded by the InSight lander during its first 200 sols on Mars are presented. In addition to the geometric variation in illumination on seasonal and diurnal ...timescales, the data are influenced by dust suspended in the atmosphere and deposited on the solar panels. Although no dust devils have been detected by InSight's cameras, brief excursions in solar array currents suggest that at least some of the vortices detected by transient pressure drops are accompanied by dust. A step increase in array output (i.e., a “cleaning event”) was observed to be directly associated with the passage of a strong vortex. Some quasiperiodic variations in solar array current are suggestive of dust variations in the planetary boundary layer. Nonzero array outputs before sunrise and after sunset are indicative of scattering in the atmosphere: A notable increase in evening twilight currents is observed associated with noctilucent clouds, likely of water or carbon dioxide ice. Finally, although the observations are intermittent (typically a few hours per sol) and at a modest sample rate (one to two samples per minute), three single‐sample light dips are seen associated with Phobos eclipses. These results demonstrate that engineering data from solar arrays provide valuable scientific situational awareness of the Martian environment.
Key Points
Solar array current telemetry gives situational awareness of the Mars surface environment
Dust in the atmosphere is observed to vary
Twilight currents indicate clouds
Spirit began operations in Gusev Crater in January 2004 and has returned data on three seasons of dust devil (DD) activity. Total DDs observed were 533 in season one, 101 in season two, and 127 in ...season three. Their general characteristics are the same within factors of 2 among the seasons, with median diameters of 19 m in season one, 24 m in season two, and 39 m in season three, and dust flux values for individual vortices ranging from 4.0 × 10−9 to 4.6 × 10−4 kg m−2 s−1 in season one, 5.2 × 10−7 to 6.2 × 10−5 kg m−2 s−1 in season two, and 1.5 × 10−7 to 1.6 × 10−4 kg m−2 s−1 in season three. All three seasons were initiated with the onset of southern Martian spring within 14 sols of the same Ls (181°) and their frequency increased to the period corresponding to late southern spring. The occurrences decreased monotonically in seasons one and three but apparently ended abruptly in season two when a large dust storm occurred; although the dusty atmosphere might have precluded the detection of active DDs, the abrupt cessation could result from conditions such as thermal stability of the atmosphere due to the presence of dust which could halt DD formation. Dust devils can contribute significant quantities of dust to the atmosphere, although it is unclear as to whether this dust stays locally or is injected into higher‐altitude winds and is distributed elsewhere. In the three DD seasons observed through Spirit, DDs in Gusev Crater injected a minimum average of ∼18 × 106 kg of material into the atmosphere each season.
•Calculations indicate the air within Gale Crater is less dusty than expected.•Low dust within the crater reconciles column optical depths at MER-B and MSL.•REMS and Navcam comparison indicate ...vortices are unable to raise dust at Gale.•One optically thick dust devil is observed at 3-sigma level and described.•Dustless vortices, low in-crater dust consistent with modeled suppressed PBL modeled suppressed PBL.
The Navigation Cameras (Navcam) of the Mars Science Laboratory rover, Curiosity, have been used to examine two aspects of the planetary boundary layer: vertical dust distribution and dust devil frequency. The vertical distribution of dust may be obtained by using observations of the distant crater rim to derive a line-of-sight optical depth within Gale Crater and comparing this optical depth to column optical depths obtained using Mastcam observations of the solar disc. The line of sight method consistently produces lower extinctions within the crater compared to the bulk atmosphere. This suggests a relatively stable atmosphere in which dust may settle out leaving the air within the crater clearer than air above and explains the correlation in observed column opacity between the floor of Gale Crater and the higher elevation Meridiani Planum. In the case of dust devils, despite an extensive campaign only one optically thick vortex (τ=1.5±0.5×10−3) was observed compared to 149 pressure events >0.5Pa observed in REMS pressure data. Correcting for temporal coverage by REMS and geographic coverage by Navcam still suggests 104 vortices should have been viewable, suggesting that most vortices are dustless. Additionally, the most intense pressure excursions observed on other landing sites (pressure drop >2.5Pa) are lacking from the observations by the REMS instrument. Taken together, these observations are consistent with pre-landing circulation modeling of the crater showing a suppressed, shallow boundary layer. They are further consistent with geological observations of dust that suggests the northern portion of the crater is a sink for dust in the current era.
PDF
