An atom interferometer under development to measure gravitational ripples in space-time with picometer-level sensitivity could also advance geodesy, the science of measuring the Earth’s size, shape and gravitational field. Technologists at NASA’s Goddard Space Flight Center were recently awarded Phase 2 funding from the NASA Innovative Advanced Concepts program to continue developing an atom interferometer they hope will one day be able to detect gravitational ripples in space-time caused when massive celestial objects move and disrupt the space around them. In atom interferometry, atoms are cooled to near absolute zero using a laser. At these temperatures, the atom behaves more like a wave, and its velocity slows to nearly zero. By firing another series of laser pulses at the laser-cooled atoms, scientists put them into what they call a “superposition of states.” The atoms have different momenta, permitting them to separate spatially and be manipulated to fly along different trajectories. Eventually, they cross paths and recombine at the detector. An atom interferometer can detect whether the path an atom takes varies by even a picometer. With this level of precision, the technology could not only map Earth’s gravitational field but also chart how it changes over time. The Earth’s gravitational field changes for various reasons, including the influences of the sun and moon, but the most significant is “the change in water mass, which includes Earth’s ice sheets, oceans, groundwater, lakes and rivers,” commented Scott Luthcke, a scientist at the Goddard Planetary Geodynamics Laboratory. “If a glacier or ice sheet melts, this will affect mass distribution and, therefore, the Earth’s gravitational field.” Luthcke believes that by gathering both spatial and temporal measurements, atom interferometry could provide scientists with another tool for studying the Earth’s response to climate change. For more information, visit: www.gsfc.nasa.gov