By Gerry Harp
I gave a poster the first week of January at the 2010 conference of the American Astronomical Society in Wash. D.C. Rob, my coworker, playfully wrote WOW! on one of my graphs (see below). This is a signal that we observed using the Allen Telescope Array last summer with my student, Bethany Wilcox, during her summer internship at the SETI Institute.
This signal was observed in just one of ~7 radio SETI searches going on at the Institute. It shows a narrow bandwidth burst of energy that appeared in our receivers on July 21, 2009, at about 1pm Pacific Time. This signal has many properties we would associate with an ET signal. For example, it appears close to the "magic" frequency of 4462 MHz, the number PI times the HI spectral line of atomic Hydrogen (1.42 MHz). This is the same frequency that Carl Sagan used for the signal in his novel Contact. Unfortunately, this signal was observed only one time, and then it was gone. Several re-observations did not show anything like this again.
While this signal is especially intriguing, no one should get excited yet. (Please don't call the Enquirer!) We see similar signals every day. Signals come and go, and if they're not persistent we move on. That is, the signal must be continuous or regularly reappear so that we can perform multiple tests on the signal to prove it is really coming from outer space. (One final test would be to call another observatory and ask them to look and see if they see the same thing.) If the signal isn't persistent, then most probably and based on our experience, it was generated by human-made equipment right here on Earth.
Presently, we can measure only a small part of the sky and a small frequency bandwidth at a time. One day we hope to have an all-sky, all-frequency monitoring system which will enable us to follow up signals like this one for a long period of time. For now our best strategy is to give up on one-offs and look for signals that stay put long enough for us to take their temperature.
In future blogs I intend to say more about searches at the SETI Institute and fill you in on our results.