Scientists announced in 2009 that for the first time, they have found evidence of lightning during a dust storm in Mars.
While dust storms occur quite frequently in Mars, subsequent observations using the European Space Agency's Mars Express spacecraft and the Allen Telescope Array in California failed to detect another lightning. This suggested that lightning might not happen as often on the Red Planet as they do on Earth. In a new study, researchers found out why.
Recreating A Martian Dust Storm
To investigate, the team used grains of dark volcanic rocks, called basalt, that are common on the surface of Mars to recreate conditions that could produce bolts of lightning during dust storms. They placed spherical grains of basalt (about 1 to 2 millimeters wide each) on a plate that vibrated for 30 minutes to generate an electric charge through what is called a "triboelectric effect."
The researchers also varied the air pressure from 0.03 millibars to 80 millibars in which the experiment took place. For context, in Mars has an average atmospheric pressure of 6 millibars, ranging from less than 1 millibar atop the highest volcanoes to more than 10 millibars in the deepest valleys.
They extracted the grains of basalt from the plate to measure their level of charge.
Low Air Pressure On Mars
They found that the grains of basalt hardly had difficulty accumulating electric charge when the air pressure is low. The charges on grains tested in the range of Martian air pressures are at least five times smaller compared to the highest air pressures during the experiment. This results in less frequent and less energetic lightning on Mars.
On Earth, the average atmospheric pressure at sea level is about 1,000 millibars.
Gerhard Wurm, a planetary scientist at the University of Duisburg-Essen in Germany, explained to Space that the study proves "tribocharging works the least for sand-sized grains", especially with the low atmospheric pressure.
Wurm also said that it is not likely for cosmic rays from deep space or ultraviolet radiation from the sun to produce lightning because they might not be strong enough on Mars.
The findings were published in the October issue of the journal Icarus.