It has been a few months since we last posted a science newsletter. During this time we've been working hard to identify and compare the most promising signal candidates found by SETI@home users. We define candidates as two or more events (events can be spikes, Gaussians, triplets, or pulses) detected from the same location in space at different times.

In fact, we have an opportunity to re-observe a few of our very best candidates at Arecibo within the next few months. So how do we decide which of our thousands of candidates have the most potential? We consider a candidate exceptional if it exhibits one or more of the following characteristics:

• Its location matches the location of a known star.
• Its location matches the location of a known planet.
• Its barycentric frequency is constant across time but cannot be attributed to RFI.

Matching Candidates to Known Stars and Planets

Matching up a candidate to a specific planet or star is like obtaining a return address. We want to examine these instances first before delving into candidates that don't have an obvious possible source. To learn more about nearby stars, see RECONS (the Research Consortium on Nearby Stars). For more information about extrasolar planets, visit the California and Carnegie Planet Search website.

The Significance of a Constant Barycentric Frequency

Why is a constant barycentric frequency such an important consideration? The answer relates to the fact that the Earth, the sun, and all celestial bodies are spinning and whirling around in the universe. When we receive radio signals at Arecibo, we're spinning and rotating relative to those incoming signals, which makes their frequency rise and fall over time. (This phenomenon is known as the Doppler Effect.) When we calculate the barycentric frequency for a signal, we're figuring out the frequency we'd detect if we weren't spinning and rotating around the sun. Now here's the really interesting part: If an incoming signal shows a constant barycentric frequency over time, it means the source of the signal is not spinning or rotating relative to us. The likelihood of such a circumstance occuring by chance is extremely small. Instead, a constant barycentric frequency implies that the sender is taking the source location's spin and rotation into account when sending the signal—an intelligent source.

We have not yet completed our short list of top candidates for the upcoming re-observation, but we're getting close. It will be the first of many opportunities to review our most promising signals, and we expect to discover many new quality candidates as more results come in from the SETI@home community. Keep on crunching!

Coming Soon: Triplet and pulse candidates, meta-candidates, and recently identified RFI patterns.

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