One existing theory is that photoreceptors in a bird's retina absorb light, which causes a chemical reaction that, in turn, produces a short-lived photochemical species whose lifetime is sensitive to the magnitude and direction of a weak magnetic field.
The photoreceptor theory is supported by the fact that blue light photoreceptors have been detected in retinas of migratory birds when they perform magnetic orientation. However, it has not been confirmed in the field or the lab that a magnetic field as weak as Earth's can produce detectable changes within a photochemical molecule; nor, has a photochemical molecule been shown to respond to the direction of such a magnetic field until now.
The U.S. and U.K. researchers have demonstrated that a synthesized photochemical molecule composed of linked carotenoid, porphyrin and fullerene units can act as a magnetic compass. Carotenoid is an organic pigment that occurs naturally in plants and other photosynthetic organisms. Porphyrin is similar to a chlorophyll molecule and exists in green leaves and red blood cells. Fullerene is composed entirely of carbon, and a spherical fullerene is known as a "buckyball."
Under normal conditions, each of the outer electron orbitals of the linked carotenoid (C), porphyrin (P) and fullerene (F) units contain two paired electrons. In the pair, the magnetic "north" pole of one electron is matched with the magnetic "south" pole of the other, causing it to be non-magnetic. As all of its electrons are paired, the CPF molecule has a neutral charge and exists in its lowest energy or ground state. Alternatively, when a CPF molecule is exposed to light, porphyrin absorbs the light energy and moves into a higher energy or excited state.
Porphyrin's excited state induces a carotenoid electron to leave its partner electron and move to fullerene's outer orbital. Since the transfer of the
|Contact: Jennifer Grasswick|
National Science Foundation