Dust devil and the details: Spinning up a storm on Mars

A dust devil reaching half a mile above the plain of Amazonis Planitia is twisted by the wind at different levels above the surface. Credit: NASA/JPL/University of Arizona photo

Spinning up a dust devil in the thin air of Mars requires a stronger updraft than is needed to create a similar vortex on Earth, according to research at The University of Alabama in Huntsville (UAH).

Early results from this research in UAH's Atmospheric Science Department are scheduled for presentation today at the American Geophysical Union's fall meeting in San Francisco.

"To start a dust devil on Mars you need convection, a strong updraft," said Bryce Williams, an atmospheric science graduate student at UAH. "We looked at the ratio between convection and surface turbulence to find the sweet spot where there is enough updraft to overcome the low level wind and turbulence. And on Mars, where we think the process that creates a vortex is more easily disrupted by frictional dissipation -- turbulence and wind at the surface -- you need twice as much convective updraft as you do on Earth."

Williams and UAH's Dr. Udaysankar Nair looked for the dust devil sweet spot by combining data from a study of Australian dust devils with meteorological observations collected during the Viking Lander mission. They used that data and a one-dimensional Mars planetary boundary layer model to find thresholds of the ratio between convection and surface friction velocities that identify conditions conducive to forming dust devils.

While dust devils on Earth are seldom more than meteorological curiosities, on Mars they sometimes grow to the size of terrestrial tornados, with a funnel more than 100 meters wide stretching as much as 12 miles above the Martian surface.

Williams and Nair are looking at the effects dust devils have on lifting dust into the Martian atmosphere. Dust in the Martian air and its radiative forcing are important modulators of the planet's climate.

"The Martian air is so thin, dust has a greater effect on energy transfers in the atmosphere and on the surface than it does in Earth's thick atmosphere," said Nair, an associate professor of atmospheric science. Dust in the Martian air cools the surface during the day and emits long-wave radiation that warms the surface at night.

Source: University of Alabama Huntsville

Making measurements when a comet passes close to Mars

Comet Siding Spring and Mars. Credit: Artist's impression: NASA

On Sunday 19 October at 20:29 CET a comet will pass close to the planet Mars. At the same time the Swedish instrument ASPERA-3 is on board the European satellite Mars Express orbiting Mars and ready to make measurements.

"No one has before made measurements when a comet passes so close by a planet," says Associate Professor Mats Holmström at the Swedish Institute of Space Physics in Kiruna, Sweden.

The comet Siding Spring will pass by Mars at a distance of only 140,000 km, about a third of the distance from the Earth to the Moon, by way of comparison. The outer parts of the comet's thin atmosphere will collide at high speed (56 km/sec) with the atmosphere of Mars.

"We expect that gas and dust from the comet will impact on the Martian atmosphere, which will be temporarily heated and will expand," says Mats Holmström. "We should be able to see that with our instrument."

The Swedish Institute of Space Physics (IRF) has Principal Investigator responsibility for the satellite instrument ASPERA-3 which is an international collaboration with participants from some 15 research groups from about 10 countries. ASPERA-3 on board the measures how charged particles from the sun, the so-called solar wind, influences the atmosphere of Mars. Mars Express was lauched by the European Space Agency (ESA) and has been orbiting Mars since 2003.

Source: Expertsvar

Traces of Martian biological activity could be locked inside a meteorite

Ejected from Mars after an asteroid crashed on its surface, the meteorite, named Tissint, fell on the Moroccan desert on July 18, 2011, in view of several eyewitnesses. Upon examination, the alien rock was found to have small fissures that were filled with carbon-containing matter. Credit: Copyright Alain Herzog/EPFL

Did Mars ever have life? Does it still? A meteorite from Mars has reignited the old debate. An international team that includes scientists from EPFL has published a paper in the scientific journal Meteoritics and Planetary Sciences, showing that martian life is more probable than previously thought.

"So far, there is no other theory that we find more compelling," says Philippe Gillet, director of EPFL's Earth and Planetary Sciences Laboratory. He and his colleagues from China, Japan and Germany performed a detailed analysis of organic carbon traces from a Martian meteorite, and have concluded that they have a very probable biological origin. The scientists argue that carbon could have been deposited into the fissures of the rock when it was still on Mars by the infiltration of fluid that was rich in organic matter.

Ejected from Mars after an asteroid crashed on its surface, the meteorite, named Tissint, fell on the Moroccan desert on July 18, 2011, in view of several eyewitnesses. Upon examination, the alien rock was found to have small fissures that were filled with carbon-containing matter. Several research teams have already shown that this component is organic in nature. But they are still debating where the carbon came from.

Maybe biological, but not from our planet

Chemical, microscopic and isotope analysis of the carbon material led the researchers to several possible explanations of its origin. They established characteristics that unequivocally excluded a terrestrial origin, and showed that the carbon content were deposited in the Tissint's fissures before it left Mars.

The researchers challenged previously described views (Steele et al., Science, 2012) proposing that the carbon traces originated through the high-temperature crystallization of magma. According to the new study, a more likely explanation is that liquids containing organic compounds of biological origin infiltrated Tissint's "mother" rock at low temperatures, near the Martian surface.

These conclusions are supported by several intrinsic properties of the meteorite's carbon, e.g. its ratio of carbon-13 to carbon-12. This was found to be significantly lower than the ratio of carbon-13 in the CO2 of Mars's atmosphere, previously measured by the Phoenix and Curiosity rovers. Moreover, the difference between these ratios corresponds perfectly with what is observed on Earth between a piece of coal -- which is biological in origin -- and the carbon in the atmosphere. The researchers note that this organic matter could also have been brought to Mars when very primitive meteorites -- carbonated chondrites -- fell on it. However, they consider this scenario unlikely because such meteorites contain very low concentrations of organic matter.

"Insisting on certainty is unwise, particularly on such a sensitive topic," warns Gillet. "I'm completely open to the possibility that other studies might contradict our findings. However, our conclusions are such that they will rekindle the debate as to the possible existence of biological activity on Mars -- at least in the past."

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Source: Ecole Polytechnique Fédérale de Lausanne