François Lique

Two guitar strings are stretched on the same neck. They are almost identical, but one is slightly shorter — and they sound different. That's roughly how the two isomers of ethanimine work: molecules with the same set of atoms but rotated differently in space. Astronomers spotted this molecule in the dense clouds near the center of our Galaxy.

In the cold cloud TMC-1, where the temperature never rises above ten degrees above absolute zero, molecules rarely encounter one another. But every so often a helium atom whizzes past, and that brief touch is enough to alter the molecule's rotation. Such collisions dictate what radiation we see from Earth.