Sky Surveys: Serendip IV, BETA and Argus

There are two types of searches on the telescopes today. There are sky surveys in which you look every place that you can. However, you are not able to spend very much time at any one frequency at any point in the sky if you are going to look at the whole sky.

Suppose that the luminosity function for transmitters is like the luminosity function for stars. When you go out at night and look up at the sky, the bright stars that you see are not the closest stars. The close stars are the little faint ones. The bright stars are intrinsically much, much brighter than the nearby stars, and they are much, much farther away.

It might be the same for extraterrestrial transmitters that the most detectable transmitter is coming from very far away in a direction that you would not otherwise think to point your telescope. If you do a limited sensitivity survey of the entire sky you may stumble on it where you would miss it pointing your telescope in directions that you already knew about.

There are a number of such sky survey programs on the telescope today. The most systematic is the Serendip IV (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) search. It is being carried out at the Arecibo Observatory, the world's largest radiotelescope. Serendip IV searches a hundred megahertz of the spectrum near the hydrogen line. In the new SETI-at-Home project, two megahertz of that spectrum will be put onto tape and sent to Berkeley, where it will go on a server. From there it will be distributed to ordinary folks running screensavers who want to participate in real-time sensitive signal detection.

Serendip IV can only do a very first high-level cut at the data reduction. But on this very small fraction of the bandwidth, by using distributed processing on home PCs, it is possible get enough compute cycles to do a very thorough frequency/time analysis of the data looking for signals. Serendip IV is funded by the SETI Institute and by the Planetary Society.

Another project is BETA (Billion-channel Extraterrestrial Assay), which uses a 26-meter telescope at Harvard College’s Agassiz Station (Oak Ridge Observatory). The program is run by Paul Horowitz, professor of physics at Harvard, and it is also funded by the Planetary Society.

META (Megachannel Etraterrestrial Assayis) was an earlier version of BETA and it is currently being operated in Argentina. There is also a Southern Serendip in Australia using the Parkes radiotelescope. The Southern Serendip is surveying the southern sky.

Lastly, there is a new project being developed called project Argus. It will attempt to organize 5,000 volunteers around the world with backyard satellite dishes. These will form a network of very low sensitivity but continuous observation of the sky, looking for very strong but perhaps transient events. The project organization is based on the model of the Association of Variable Star Observers, a group of amateur astronomers who have been extremely useful in optical astronomy over the years.

Contributed by: Dr. Jill Tarter and Jim Miller