Measurements of the geomagnetic field at the smallest scales are used to locate sunken ships and mineral-rich geological formations. Large-scale measurements probe properties of Earth’s core. At length scales of tens to hundreds of kilometers, geomagnetic maps yield clues about the chemical dynamics in Earth’s outer mantle and the effects of ionic currents on ocean circulation. To avoid ground-based electromagnetic interference, geomagnetometers are typically placed aboard orbiting satellites, which are deployed sporadically and at a relatively high cost. Now, an international team of scientists led by James Higbie (Bucknell University), Domenico Bonaccini Calia (European Southern Observatory), and Dmitry Budker (University of California, Berkeley) has proposed a lower-cost ground-to-space system that exploits the interaction of beams from ground-based lasers with sodium atoms in the mesosphere, about 90 km above Earth's surface. The team’s system would harness the existing and expanding infrastructure of high-powered lasers that generate artificial stars for optical telescopes by exciting mesospheric sodium. As shown in the image, an optically pumped laser would spin polarize the sodium atoms, and then a ground-based telescope would measure the fluorescence intensity, which is dependent on the atoms’ precession frequency in the magnetic field. The researchers calculate that such a system would achieve subnanotesla sensitivity and could lead to the formation of a global network for continuous mapping and monitoring of mesospheric magnetic fields. (J. M. Higbie et al., Proc. Natl. Acad. Sci. USA, in press, doi:10.1073/pnas.1013641108.)—Jermey N. A. Matthews
