杏吧原创

NASA鈥檚 Perseverance rover has spotted the first visible light aurora on Mars, suggesting that future astronauts visiting the Red Planet could be in for a light show.

Astronomers have observed aurorae, the light produced when particles or radiation hits a planet鈥檚 atmosphere, on Mars since 2005, but all of these displays have only been detected in the form of ultraviolet light, which is invisible to the naked human eye. These come from oxygen in the atmosphere being energised by charged particles coming from the sun. The oxygen then loses this extra energy by releasing light at specific frequencies called emission lines.

鈥淲e know from quantum mechanics that some of these oxygen lines should also produce aurora emissions in the visible [range],鈥� at the University of Oslo in Norway told the Europlanet Science Congress in Berlin, Germany, on 10 September. 鈥淪o there鈥檚 been this expectation for some time, but we haven鈥檛 actually caught it on camera or with another sensor up until this point.鈥�

Now, Knutsen and her colleagues have spotted a green aurora of visible light using the Perseverance rover鈥檚 on-board camera and spectrometer. The vehicle captured the display on 18 March, three days after a powerful coronal mass ejection from the sun..

During the event, Knutsen and her team measured a spike at the exact wavelength that oxygen produces visible light 鈥� this same emission gives rise to the green colours seen during aurorae on Earth. While the intensity of the light was too weak for humans to see, equivalent to a faint aurora here on Earth, future events could be bright enough for any astronauts living on the Red Planet to see unaided.

One issue for any future Martian sky watchers is that the same stream of charged particles responsible for generating the lights can also be harmful to humans, but the occasional observation should be OK, says at Aberystwyth University, UK.

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鈥淢ars鈥檚 atmosphere is thick enough to protect you from the worst of the radiation effects that you would get from energetic particle storms,鈥� he says, with the resulting radiation dose equivalent to that of a chest X-ray. 鈥淪o you could actually lie flat on your back and look up at this stuff and see the visible aurora and you wouldn鈥檛 get fried.鈥�

Knutsen wouldn鈥檛 allow New 杏吧原创 to publish the photograph of the Martian aurora, as the team鈥檚 work is currently under peer review, but she did display it during her conference presentation. It consists of a grainy, night-time Martian scene with a vague greenish hue. 鈥淚 have shown this to a few people and the reaction I most commonly get is 鈥榳here is the aurora?鈥� So, I just want to remind everyone 鈥� the diffuse aurora is everywhere, it鈥檚 the greenish-yellow colour that you see over the whole image,鈥� said Knutsen.