Martian lightning

In a dust storm, scientists find the first direct evidence of electrical discharge on Mars

Scientists say they have seen the first direct evidence of lightning on Mars, in the form of electrical discharges during a Martian dust storm.

ELECTRICAL DUST Lightning has been detected for the first time on Mars, and it may look something like this artist’s illustration. Bits of debris in a dust devil rub against one another and then discharge, causing a faint glow like the one at the bottom of the image. University of Michigan

The finding has implications for human travel to the Red Planet and for studying possible origins of life on Mars, the authors say in a paper to appear in Geophysical Research Letters.

It has been thought that lightning might be possible on Mars. Bits of dust rubbing against each other in one of the planet’s famous dust devils could charge up the particles the same way that running on a carpet charges up socks. All that charge could then be discharged in a zap, either as lightning or a shock.

But catching Martian lightning in the act was difficult: The lightning bursts were too small to distinguish from the energy emanating from the planet itself. And the dust storms themselves obscured the faint glow that might have been visible from just above the red planet.

To “see” the lightning, researchers from the University of Michigan and colleagues used a new detector that can distinguish microwave radiation emanating from natural objects like dirt and rocks from a burst of lightning. Radiation from natural objects, including Martian rocks, is relatively constant; radiation from lightning displays changes in the distribution of frequencies of light.

Using a 34-meter-diameter radio telescope in the California desert, for about five hours a day for 12 days between May 22 and June 16, 2006, the researchers found no signs of the variable radiation, except during a period of two or three hours. At that time a Martian dust storm was on the side of Mars facing the scientists’ detector. “Every time we moved off Mars the [signal] went away. Then we moved it back and it came back again,” says Christopher Ruf of the University of Michigan in Ann Arbor, one of the study’s authors.

Lightning as an explanation for the results makes sense, says geophysicist Phil Christensen of Arizona State University in Tempe. “I can’t think of a better explanation,” he says. “They found it to be in a dust storm, and that’s exactly where you’d expect it.”

Lightning on Mars is probably fainter and more diffuse than the lightning commonly observed on Earth, says Nilton Renno, another author of the study. “The atmosphere [on Mars] is much less dense,” he says. Instead of forks of lightning, Martian lightning bursts would cover a wider area and would have a “faint glow” like the light in a neon tube.

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