Mars' emitted energy and seasonal energy imbalance

SignificanceThe radiant energy budget is a fundamental metric for planets. Based on the observations from multiple missions, we provide a global picture of Mars' emitted power. Furthermore, we estimate the radiant energy budget of Mars, which suggests that there are energy imbalances at the time scale of Mars' seasons. Such energy imbalances provide a new perspective to understanding the generating mechanism of dust storms. Mars' radiant energy budget is assumed to be balanced at all time scales in current models and theories, but our analyses show that the energy budget is not balanced, at least at the time scale of Mars' seasons. Therefore, current theories and models should be revisited with the newly revealed energy characteristics.

The Reflectivity of Mars at 1064 nm: Derivation from Mars Orbiter Laser Altimeter Data and Application to Climatology and Meteorology

The Mars Orbiter Laser Altimeter (MOLA) on board Mars Global Surveyor (MGS) made > 10⁸ measurements of the reflectivity of Mars at 1064 nm (R ₁₀₆₄) by both active sounding and passive radiometry. Past studies of R ₁₀₆₄ neglected the effects of atmospheric opacity and viewing geometry on both active and passive measurements and also identified a potential calibration issue with passive radiometry. Therefore, as yet, there exists no acceptable reference R ₁₀₆₄ to derive a column opacity product for atmospheric studies and planning future orbital lidar observations. Here, such a reference R ₁₀₆₄ is derived by seeking R 1064 M , N : a Minnaert-corrected normal albedo under clear conditions and assuming minimal phase angle dependence. Over darker surfaces, R 1064 M , N and the absolute level of atmospheric opacity were estimated from active sounding. Over all surfaces, the opacity derived from active sounding was used to exclude passive radiometry measurements made under opaque conditions and estimate R 1064 M , N . These latter estimates then were re-calibrated by comparison with R^M,N derived from Hubble Space Telescope (HST) observations over areas of approximately uniform reflectivity. Estimates of R 1064 M , N from re-calibrated passive radiometry typically agree with HST observations within 10 %. The resulting R 1064 M , N is then used to derive and quantify the uncertainties of a column opacity product, which can be applied to meteorological and climatological studies of Mars, particularly to detect and measure mesoscale cloud/aerosol structures.

The physics of wind-blown sand and dust

The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols. This paper presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars. Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices. We also discuss the physics of wind-blown sand and dune formation on Venus and Titan.

Global warming and climate forcing by recent albedo changes on Mars

For hundreds of years, scientists have tracked the changing appearance of Mars, first by hand drawings and later by photographs. Because of this historical record, many classical albedo patterns have long been known to shift in appearance over time. Decadal variations of the martian surface albedo are generally attributed to removal and deposition of small amounts of relatively bright dust on the surface. Large swaths of the surface (up to 56 million km2) have been observed to darken or brighten by 10 per cent or more. It is unknown, however, how these albedo changes affect wind circulation, dust transport and the feedback between these processes and the martian climate. Here we present predictions from a Mars general circulation model, indicating that the observed interannual albedo alterations strongly influence the martian environment. Results indicate enhanced wind stress in recently darkened areas and decreased wind stress in brightened areas, producing a positive feedback system in which the albedo changes strengthen the winds that generate the changes. The simulations also predict a net annual global warming of surface air temperatures by approximately 0.65 K, enhancing dust lifting by increasing the likelihood of dust devil generation. The increase in global dust lifting by both wind stress and dust devils may affect the mechanisms that trigger large dust storm initiation, a poorly understood phenomenon, unique to Mars. In addition, predicted increases in summertime air temperatures at high southern latitudes would contribute to the rapid and steady scarp retreat that has been observed in the south polar residual ice for the past four Mars years. Our results suggest that documented albedo changes affect recent climate change and large-scale weather patterns on Mars, and thus albedo variations are a necessary component of future atmospheric and climate studies.

Soils of Eagle Crater and Meridiani Planum at the Opportunity Rover Landing Site

The soils at the Opportunity site are fine-grained basaltic sands mixed with dust and sulfate-rich outcrop debris. Hematite is concentrated in spherules eroded from the strata. Ongoing saltation exhumes the spherules and their fragments, concentrating them at the surface. Spherules emerge from soils coated, perhaps from subsurface cementation, by salts. Two types of vesicular clasts may represent basaltic sand sources. Eolian ripples, armored by well-sorted hematite-rich grains, pervade Meridiani Planum. The thickness of the soil on the plain is estimated to be about a meter. The flatness and thin cover suggest that the plain may represent the original sedimentary surface.

Sedimentary rocks of early Mars

Layered and massive outcrops on Mars, some as thick as 4 kilometers, display the geomorphic attributes and stratigraphic relations of sedimentary rock. Repeated beds in some locations imply a dynamic depositional environment during early martian history. Subaerial (such as eolian, impact, and volcaniclastic) and subaqueous processes may have contributed to the formation of the layers. Affinity for impact craters suggests dominance of lacustrine deposition; alternatively, the materials were deposited in a dry, subaerial setting in which atmospheric density, and variations thereof mimic a subaqueous depositional environment. The source regions and transport paths for the materials are not preserved.