* Astronomy

Blobrana · L

RE: Mars Dust Devil

Blobrana · L

Title: Dust aerosol, clouds, and the atmospheric optical depth record over 5 Mars years of the Mars Exploration Rover mission
Author: Mark T. Lemmon, Michael J. Wolff, James F. Bell III, Michael D. Smith, Bruce A. Cantor, Peter H. Smith

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 1 {\mu}m effective radius during northern summer and a 2 {\mu}m effective radius at the onset of a dust lifting event. The solar longitude (LS) 20-136{\deg} period is also characterized by the presence of cirriform clouds at the Opportunity site, especially near LS=50 and 115{\deg}. 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.

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Blobrana · L

Title: Measurements of Martian Dust Devil Winds with HiRISE
Authors: David S. Choi, Colin M. Dundas

We report wind measurements within Martian dust devils observed in plan view from the High Resolution Imaging Science Experiment (HiRISE) orbiting Mars. The central colour swath of the HiRISE instrument has three separate charge-coupled devices (CCDs) and colour filters that observe the surface in rapid cadence. Active features, such as dust devils, appear in motion when observed by this region of the instrument. Our image animations reveal clear circulatory motion within dust devils that is separate from their translational motion across the Martian surface. Both manual and automated tracking of dust devil clouds reveal tangential winds that approach 20-30 m/s in some cases. These winds are sufficient to induce a ~1% decrease in atmospheric pressure within the dust devil core relative to ambient, facilitating dust lifting by reducing the threshold wind speed for particle elevation. Finally, radial velocity profiles constructed from our automated measurements test the Rankine vortex model for dust devil structure. Our profiles successfully reveal the solid body rotation component in the interior, but fail to conclusively illuminate the profile in the outer regions of the vortex. One profile provides evidence for a velocity decrease as a function of r^-½, instead of r^-1, suggestive of surface friction effects. However, other profiles do not support this observation, or do not contain enough measurements to produce meaningful insights.

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Blobrana · L

Dust-devils flirt with Curiosity Mars rover

Nasa's Curiosity rover has been getting a good feel for the weather on Mars.
Although no cameras have yet caught sight of them, it seems whirlwinds of dust have been skirting around the six-wheeled vehicle.
From the data gathered by Curiosity's meteorological station, scientists think dust-devils may even have run over the robot.
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Blobrana · L

No dia 14 de Março de 2012, a Mars Reconnaissance Orbiter, fotografou um redemoinho de poeira marciana com cerca de 20 quilômetros de altura. Apesar disso, a pluma tem pouco mais de 70 metros.

Blobrana · L

A Monster Dust Devil Stalks the Martian Landscape

A dust devil the size of a terrestrial tornado towers above the Martian surface in this late springtime afternoon image of Amazonis Planitia.
Also captured by the Context Camera on MRO, the length of the shadow indicates that the dust plume reached a height of 20 kilometres above the surface! Despite its gargantuan height, the plume is only 70 metres in diameter, giving it a snake-like appearance that is twisted by high altitude winds, similar to another dust devil spotted recently in this region.
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Blobrana · L

NASA Mars Orbiter Catches Twister in Action

Credit: NASA/JPL-Caltech/Univ. of Arizona

An afternoon whirlwind on Mars lofts a twisting column of dust more than 800 meters high in an image from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.
HiRISE captured the image on Feb. 16, 2012, while the orbiter passed over the Amazonis Planitia region of northern Mars. In the area observed, paths of many previous whirlwinds, or dust devils, are visible as streaks on the dusty surface.
The active dust devil displays a delicate arc produced by a westerly breeze partway up its height. The dust plume is about 30 yards or meters in diameter.