The first modern SETI experiment – Frank Drake’s observations at Green Bank in 1960 – focused on two specific stars: Epsilon Eridani and Tau Ceti. Six decades later, astronomers have targeted another star for SETI observations: Gliese 581. This red dwarf star, which is about 20 light years distant, is not an unreasonable target: it has planets, two of which may be superEarths that are on the edge of the star’s habitable zone. What makes this particular SETI study interesting, however, is that it uses a technique that hasn’t been tried before in a SETI context: very long baseline interferometry (VLBI).
Hayden Rampadarath, and three colleagues from Curtin University in Australia, used the Australian Long Baseline Array (ALBA) in their work. This is a collection of three radio telescopes, separated by several hundred kilometres, which (once the signals from the different telescopes are combined) has an angular resolution that’s similar to the Hubble Space Telescope. The team used ALBA to observe Gliese 581 for a total of eight hours in June 2007, tuning in to frequencies near the waterhole. They discovered 222 candidate SETI signals, all of which were quickly excluded (and probably come from communications with geostationary satellites).
The interest in this paper is not that the study rules out Gliese 581 as a candidate for hosting extraterrestrial intelligence: it doesn’t. (While ALBA would pick up a transmission beamed directly to us from an Arecibo-type instrument, it obviously wouldn’t pick it up if the transmitter was pointing somewhere else or happened to be idle on the days when they looked. And ALBA wouldn’t pick up ‘leakage’ radio transmissions of the type that we typically broadcast.) No, the interest in this paper is that it demonstrates how SETI scientists can use VLBI as part of a targeted search strategy. What’s really exciting is that soon we’ll have interferometers with much more sensitivity than ALBA. The forthcoming Square Kilometer Array, in addition to being a revolutionary tool for astronomy, has the potential to enhance SETI enormously: imagine this great instrument listening to planets identified by Kepler…
You can find a preprint of Rampadarath’s paper here.