At long last, the mystery of lightning on Mars is solved
AILSA CHANG, HOST:
Lightning does not just strike on Earth. Space probes have detected flashes in the atmospheres of Jupiter and Saturn. But whether lightning happens on Mars has been a mystery for a long time. NPR's Nell Greenfieldboyce reports that scientists now say they have accidentally recorded mini lightning strikes during a dusty whirlwind.
NELL GREENFIELDBOYCE, BYLINE: For decades, researchers have thought Mars should have some form of lightning. Ralph Lorenz is a planetary scientist with the Johns Hopkins University Applied Physics Lab. He says back in the 1970s, some experimenters would put volcanic sand in a flask and pump it down to Martian atmospheric pressures.
RALPH LORENZ: And turn the lights off and swirl the sand around in the flask, and it glows.
GREENFIELDBOYCE: The glow is from electrical charges caused by the friction between the bits of sand. He says if you had a bigger buildup of static charge, you could get a more sudden discharge, like what happens with spark plugs in a car or, on a larger scale, lightning. Even here on Earth, lightning doesn't just happen in storm clouds full of water. You can see it in turbulent clouds of volcanic ash.
LORENZ: And so there's no reason that blowing sand or dust on Mars shouldn't become electrically charged.
GREENFIELDBOYCE: But no one had ever detected anything like that. Now, though, he says there's new evidence from the Mars Perseverance Rover, a car-sized robot that's been trundling around on the red planet. It's got a microphone that can record audio, like the sound of a dust devil whirling nearby. Lorenz says the recording captured the wind, the hiss of the dust.
LORENZ: And there was this, you know, one snap sound in the middle of the encounter. And we just assumed it was, you know, kind of a big sand grain or a small gravel grain just, you know, hitting the structure.
GREENFIELDBOYCE: Here's an example of what he's talking about. It's a little hard to hear, but if you listen closely, there's some wind and then a crack.
(SOUNDBITE OF WIND BLOWING)
GREENFIELDBOYCE: One of the scientists on their team wondered about this. He did experiments here on Earth showing that an electric discharge near the microphone could produce the same effect. It turns out what they had actually captured on Mars was a bit of mini lightning. It electrically interfered with the rover's microphone and had a distinctive acoustic signal. In the journal Nature, the team describes dozens of similar events. The rover's chance discovery intrigued Daniel Mitchard. He studies lightning at Cardiff University in the United Kingdom and wasn't part of the research team.
DANIEL MITCHARD: The key thing here is that we actually have a rover on the surface of Mars that appears to have detected something that fits our idea of what we think lightning on Mars would look like.
GREENFIELDBOYCE: He says if you could stand next to the rover as this happened, it's not clear what you might see. The sparks might appear as small bright flashes in the dark dust cloud.
MITCHARD: I guess that's one of the unknowns from this data is we don't really know very much about how frequent or energetic or how powerful they could be.
GREENFIELDBOYCE: He thinks this surprise find is going to spur people to try to find out and to design new instruments that could take images of Mars lightning.
Nell Greenfieldboyce, NPR News.
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