Relax: the aliens aren't using poisonous space rocks to soften us up in advance of an invasion, after all.

Last week, you may recall, a meteorite fell in Peru. Locals who were first on the scene reported feeling ill immediately after contact with the space rock, with symptoms including headaches and nausea.

Speculation began immediately as to the possible cause of the illness. Was it radiation? Alien bugs? Toxic gases? Was the meteorite a meteorite at all, or was it an explosion of marsh gas?

According to Luisa Macedo, a researcher for Peru's Mining, Metallurgy, and Geology Institute (INGEMMET), the cause of the illness was arsenic poisoning.

Speaking to National Geographic, Macedo explains that numerous arsenic deposits exist in the soils of Peru. The most likely explanation is that these deposits have contaminated the local water supply, which was vaporised when the meteorite landed.

Astronomer José Ishitsuka notes: "If the meteorite arrives incandescent and at a high temperature because of friction in the atmosphere, hitting water can create a column of steam."

The early arrivals on the scene would then inhale this water vapour, and with it small amounts of arsenic. Although arsenic can be deadly in large doses, small doses are easily survivable, provided they are not repeated. Prolonged exposure can lead to digestive problems, cancer, diabetes, liver disease and thickened skin.

Fortunately, all those who had complained of feeling sick were on the mend by last Wednesday, Macedo said. ®

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