SETI at the Green Bank Telescope

This March, Berkeley SETI is leading a collaboration that includes scientists from the SETI Institute and the National Radio Astronomy Observatory in a new effort to search for evidence of extraterrestrial intelligence on habitable planets.  This experiment will use the largest fully steerable radio telescope on the planet -- the 100 meter Green Bank Telescope in West Virginia.


The Kepler Spacecraft

The new search will target 86 exoplanet candidates uncovered by the Kepler Mission.   The Kepler Mission uses a satellite to watch for the small dip in light received from a star when an orbiting planet passes between our line of sight with the star.    So far, 1235 planet candidates have been found by the Kepler Satellite.  The 86 candidates chosen for the GBT SETI search are those in the “Habitable Zone,” that is, they are just the right distance from their parent star for liquid water to exist on their surface.


kepler planets
Locations of the Kepler Planets

The Green Bank Telescope
At optical wavelengths, only one observer can use the light received from a telescope at a given time.  At radio wavelengths, however, the signal from the telescope can actually be split many times without any loss in sensitivity.  Piggy-back SETI takes advantage of this by “listening in” on the signal from the telescope when other observers are using it, conducting independent analysis for evidence of extraterrestrial intelligence.  This way, SETI observations can be conducted much more frequently than would be possible if they required full control of the telescope.

Both searches will be performed in a region of the radio spectrum known as the “Terrestrial Microwave Window.” As shown at left, this is the region of radio frequencies that permeate both interstellar space and our own atmosphere relatively unimpeded. The GBT SETI band will include a special narrow range of frequencies within the Terrestrial Microwave Window known as the “Water Hole,” which is the region of spectrum bounded by spectral lines of the two disassociation products of water - hydrogen, H and hydroxyl, OH. Some scientists have suggested that if an extraterrestrial intelligence were to deliberately signal other intelligent beings, they might chose this band. As far as we know, all life absolutely requires water to exist.

Water Hole