Hold up your hands in front of your face. For most people, they will be mirrored copies of each other: You can hold them palm-to-palm and they will match up, but you cannot superimpose them.
Molecules also exhibit this handedness, or chirality. They come structured in two mirrored, non-superimposable forms. And it's a fascinating quirk of life that almost all biomolecules will only work in one of their two forms.
Natural amino acids – the building blocks of proteins – are almost always left-handed, or sinistral. Natural sugars like those that make up RNA and DNA, on the other hand, are almost always right-handed, or dextral. If you replace any of these molecules with the other form, the whole system breaks down.
This quirk is called homochirality. We're not sure why it happens, but it's thought to be a key property of life. And back in 2021, scientists detected molecular homochirality from a helicopter flying at a velocity of 70 kilometers per hour (43.5 mph) at an altitude of 2 kilometers (1.2 miles).
Why would they do such a thing, you ask? To see if we can detect molecular homochirality on other planets, in the search for extraterrestrial life.
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