Despite being trace constituents of the lunar exosphere, sodium and potassium are the most readily observed species due to their bright line emission. Measurements of these species by the Ultraviolet ...and Visible Spectrometer (UVS) on the Lunar Atmosphere and Dust Environment Explorer (LADEE) have revealed unambiguous temporal and spatial variations indicative of a strong role for meteoroid bombardment and surface composition in determining the composition and local time dependence of the Moon's exosphere. Observations show distinct lunar day (monthly) cycles for both species as well as an annual cycle for sodium. The first continuous measurements for potassium show a more repeatable variation across lunations and an enhancement over KREEP (Potassium Rare Earth Elements and Phosphorus) surface regions, revealing a strong dependence on surface composition.
The Lunar Atmosphere and Dust Environment Explorer (LADEE) mission was designed to address long-standing scientific questions about the Moon’s environment, including the assessment of the composition ...of the lunar atmosphere, and characterization of the lunar dust environment at low orbital altitudes. LADEE was derived from the Modular Common Spacecraft Bus design that was developed at NASA Ames Research Center; it used modularized subassemblies and existing commercial spaceflight hardware to reduce cost. LADEE was launched on the very first Minotaur V, and was also the first deep space mission launched from Wallops Flight Facility in Virginia. LADEE was equipped with two in situ instruments and a remote sensing instrument to address the atmosphere and dust measurement requirements. LADEE also carried the first deep-space optical communications demonstration, the Lunar Laser Communications Demonstration. LADEE was launched in early September, 2013, took science data for over 140 days in low lunar orbit, and impacted the surface on April 18, 2014.
Despite being trace constituents of the lunar exosphere, sodium and potassium are the most readily observed species due to their bright line emission. Measurements of these species by the Ultraviolet ...and Visible Spectrometer (UVS) on the Lunar Atmosphere and Dust Environment Explorer (LADEE) have revealed unambiguous temporal and spatial variations indicative of a strong role for meteoroid bombardment and surface composition in determining the composition and local time dependence of the Moon's exosphere. Observations show distinct lunar day (monthly) cycles for both species as well as an annual cycle for sodium. The first continuous measurements for potassium show a more repeatable variation across lunations and an enhancement over KREEP (Potassium Rare Earth Elements and Phosphorus) surface regions, revealing a strong dependence on surface composition.
Observations by several cameras on the Perseverance rover showed a 22° scattering halo
around the Sun over several hours during northern midsummer (solar longitude 142°). Such a halo has not ...previously been seen beyond Earth. The halo occurred during the aphelion cloud belt season and the cloudiest time yet observed from the Perseverance site. The halo required crystalline water-ice cloud particles in the form of hexagonal columns large enough for refraction to be significant, at least 11 μm in diameter and length. From a possible 40-50 km altitude, and over the 3.3-hour duration of the halo, particles could have fallen 3-12 km, causing downward transport of water and dust. Halo-forming clouds are likely rare due to the high supersaturation of water that is required but may be more common in northern subtropical regions during northern midsummer.
Using a 3‐D, non‐hydrostatic mesoscale Mars atmospheric model with detailed aerosol/cloud microphysics, we show that the formation of discrete afternoon clouds over the Olympus Mons volcano is due to ...the symbiosis of upslope thermal flow and a lee mountain wave circulation, and that these clouds exhibit complex particle distributions. Furthermore, we illustrate that this and other mountain‐induced circulations transport large quantities of dust, water vapor, and water ice aerosol from lower altitudes into the free atmosphere general circulation. Therefore, these circulations are an important part of Mars' net Hadley circulation and climatic forcing.
Studying lunar dust is vital to the exploration of the Moon and other airless planetary bodies. The Ultraviolet and Visible Spectrometer on board the Lunar Atmosphere and Dust Environment Explorer ...spacecraft conducted a series of Almost Limb activities to look for dust near the dawn terminator region. During these activities the instrument stared at a fixed point in the zodiacal background off the Moon's limb while the spacecraft moved in retrograde orbit from the sunlit to the unlit side of the Moon. The spectra obtained from these activities probe altitudes within a few kilometers of the Moon's surface, a region whose dust populations were not well constrained by previous remote‐sensing observations from orbiting spacecraft. Filtering these spectra to remove a varying instrumental signal enables constraints to be placed on potential signals from a dust atmosphere. These filtered spectra are compared with those predicted for dust atmospheres with various exponential scale heights and particle size distributions to yield upper limits on the dust number density for these potential populations. For a differential size distribution proportional to s−3 (where s is the particle size) and a scale height of 1 km, we obtain an upper limit on the number density of dust particles at the Moon's surface of 142 m−3.
Plain Language Summary
The Moon has a tenuous atmosphere of dust particles. It is important to study this dust environment in order to develop solutions for dust‐related problems with exploration of the lunar surface, as well as understand the effects of dust transport on other airless planetary bodies. Lunar Atmosphere and Dust Environment Explorer's Ultraviolet and Visible Spectrometer made a series of Almost Limb observations that enable us to probe the Moon's dust atmosphere at altitudes ranging from 1 and 10 km above the surface. Data from these observations are processed and compared to the predicted signals from a variety of different dust populations. These comparisons yield new upper limits on dust density within a few kilometers of the lunar surface, providing additional constraints on dust population at low altitudes.
Key Points
Lunar Atmosphere and Dust Environment Explorer’s Ultraviolet And Visible Spectrometer made a series of observations that enable us to probe the Moon's dust atmosphere at altitudes between 1 and 10 km
These observations are filtered to isolate dust signals and are compared to predicted dust atmospheres
For a dust population with power law size distribution of index −3 and scale height 1 km, the upper limit on the dust density is 142 m−3
It is suspected that the lunar exosphere has a dusty component dispersed above the surface by various physical mechanisms. Most of the evidence for this phenomenon comes from observations of “lunar ...horizon glow” (LHG), which is thought to be produced by the scattering of sunlight by this exospheric dust. The characterization of exospheric dust populations at the Moon is key to furthering our understanding of fundamental surface processes, as well as a necessary requirement for the planning of future robotic and human exploration.
We present a model to simulate the scattering of sunlight by complex lunar dust grains (i.e. grains that are non-spherical and can be inhomogeneous in composition) to be used in the interpretation of remote sensing data from current and future lunar missions. We numerically model lunar dust grains with several different morphologies and compositions and compute their individual scattering signatures using the Discrete Dipole Approximation (DDA). These scattering properties are then used in a radiative transfer code to simulate the light scattering due to a dust size distribution, as would likely be observed in the lunar exosphere at high altitudes 10's of km. We demonstrate the usefulness and relevance of our model by examining mode: irregular grains, aggregate of spherical monomers and spherical grains with nano-phase iron inclusions. We subsequently simulate the scattering by two grain size distributions (
0.1
and
0.3
μ
m
radius), and show the results normalized per-grain. A similar methodology can also be applied to the analysis of the LHG observations, which are believed to be produced by scattering from larger dust grains within about a meter of the surface.
As expected, significant differences in scattering properties are shown between the analyses employing the widely used Mie theory and our more realistic grain geometries. These differences include large variations in intensity as well as a positive polarization of scattered sunlight caused by non-spherical grains. Positive polarization occurs even when the grain size is small compared to the wavelength of incident sunlight, thus confirming that the interpretation of LHG based on Mie theory could lead to large errors in estimating the distribution and abundances of exospheric dust.
► Complex lunar dust grain modeled and their scattering properties computed. ► The scattering by a lunar exosphere composed of such is simulated. ► Comparison is made with the standard model for spherical grains. ► Significant variations in scattering are observed between the two models. ► Interpretation of observations based on spherical grains would lead to large errors.
Environmental Effects of Large Impacts on Mars Segura, Teresa L.; Toon, Owen B.; Colaprete, Anthony ...
Science (American Association for the Advancement of Science),
12/2002, Letnik:
298, Številka:
5600
Journal Article
Recenzirano
The martian valley networks formed near the end of the period of heavy bombardment of the inner solar system, about 3.5 billion years ago. The largest impacts produced global blankets of very hot ...ejecta, ranging in thickness from meters to hundreds of meters. Our simulations indicated that the ejecta warmed the surface, keeping it above the freezing point of water for periods ranging from decades to millennia, depending on impactor size, and caused shallow subsurface or polar ice to evaporate or melt. Large impacts also injected steam into the atmosphere from the craters or from water innate to the impactors. From all sources, a typical 100-, 200-, or 250-kilometers asteroid injected about 2, 9, or 16 meters, respectively, of precipitable water into the atmosphere, which eventually rained out at a rate of about 2 meters per year. The rains from a large impact formed rivers and contributed to recharging aquifers.
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