Green meteors appearing in the sky: how to explain their color?

A meteor came to ignite the sky of New Zealand two weeks ago. Small particularity compared to those usually observed, its green color! Researchers explain why.

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They would have caused the disappearance of the dinosaurs and their craters adorn the surface of the Earth. Every day, the planet is bombarded by hundreds of meteorites.

On July 7, a huge meteor crossed the skies of New Zealand. Visible in broad daylight, the racing car was also heard, creating a sonic boom over the city of Wellington and across the South Island. Two weeks later, on July 22, another meteor was captured over Canterbury, South Island. This time visible during the night, it lit up the sky nocturnal flamboyant green. These two close passages of meteors intrigued the inhabitants of the island, who asked for explanations: why this strange color green? It resembles to be mistaken the green that one can observe duringpolar aurorabut beware, the phenomenon is not the same!

No, it’s not the same green as for the aurora

When powerful solar winds cross theatmospherethey can generate what is called a Polar aurora : charged particles come into contact with those in the atmosphere and ionize them. It is the ionization of theoxygencontained in the molecules of oxygen which make up approximately 21% of the Earth’s atmosphere, which gives the characteristic green color of auroras. Indeed, after being ionized, it recombines with its electrons, which are then in a so-called excited state. The return toground state is accompanied byemission of one photonwhose wavelength corresponds to the color green.

But in the case of a meteor, the mechanism differs. The auroras usually occur between 100 kilometers and 300 kilometers in altitude, in the upper atmosphere, while meteors heat up even higher. While the piece ofasteroid heats up and ignites as it passes through the atmosphere, this time it is nickel and iron already present on the rocky body which will release a light green by vaporizing. If the meteor also contains sodiuma slightly yellow streak can be observed, when the atoms are in an excited state.

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