When the light of a distant planet is split into colors, it suddenly jumps at the boundary between red and invisible infrared, as if someone flipped a switch. This is how the vegetation red edge manifests itself: chlorophyll is transparent to near-infrared radiation, and the leaf, to avoid overheating, reflects it away. Astronomers hope to catch this same signal on Earth-like worlds with future observatories like the Habitable Worlds Observatory.

But nature has a sense of humor. A team of scientists sifted through hundreds of mineral spectra and found that ordinary pyrite, the very one that glitters like gold in souvenir shops, produces almost the same step. So do feldspars and even yellow prussiate, a potassium-iron cyanide that might have been involved in prebiotic chemistry. Each of these rocks reflects light as if pretending to be foliage.

Does this mean a future telescope will be fooled? Not necessarily. The scientists suggest looking at the neighbors: if the planet's atmosphere has abundant oxygen and methane in non-equilibrium amounts, the chance that we are facing life rises sharply. If the atmosphere resembles volcanic exhaust and the surface is strewn with sulfides, then the red edge is likely painted not by a meadow but by a rocky desert. The final verdict will come from statistics: how likely is it to encounter that particular mineral on a planet with such conditions.

So the red edge is no longer an unequivocal signature of life. It becomes a clue that must be examined alongside everything else, like a fingerprint that says nothing by itself until you compare it with a database.