Molecular handedness (chirality) is the potential of some compounds to form molecules incorporating the same combination of elements, but in two forms that geometrically differ, being reflections of each other, in the manner that a person's hands appear to be mirror reflections of each other.
In many processes that create such compounds, both hands of molecules are produced in roughly equal numbers. However, for some key molecules, life on Earth incorporates and uses only one of two such possibilities (i.e., homochirality, consistent handedness). For this reason, molecular handedness is a proposed biosignature. Because electromagnetic radiation normally doesn't reveal the handedness of the source, in situ investigation is of use to detect it. This makes it a candidate for detecting life in solar system bodies, but is less useful for extra-solar planets.