At 12 midnight, Atlantic Standard Time, on Monday, March 24, SETI@home's Stellar Countdown came to an end at the Arecibo Radio Observatory. The 24 hours of observation needed to visit the top SETI@home candidate signals should have taken three days, but instead took nearly a week. The eruption of a rare Solar flare pushed the sessions back several days, ending with a 14 hour observation marathon on Monday.
In the end, the change of plans did not matter. The Stellar Countdown proved even more successful than expected, revisiting 166 of SETI@home's most promising candidates signals. This is considerably more than the 100-150 predicted before the observations. In addition, SETI@home Chief Scientist Dan Werthimer and his team found time to target 35 nearby Sun-like stars, 15 nearby galaxies, 6 candidates from the SERENDIP SETI search, and 5 extrasolar planetary system.
All in all the Stellar countdown observed 227 promising locations in the sky. Within the next few weeks all the data collected and recorded will be processed by SETI@home users around to world, to determine whether any of the targets proves to be a true alien signal. We promise to keep you posted!
Even before getting the final results, however, SETI@home is moving forward with plans for a more sensitive and comprehensive sky survey. Within the next two years the SETI@home team hopes to phase out the aging receiver at the base of the line feed. In its place, SETI@home observations will be conducted using a new multi-beam array that will be located within the Gregorian dome.
Unlike the single needle-shaped feed now in use, the array will be composed of seven separate feeds, each connected to its own highly sensitive L-Band receiver. This means that whereas the line feed can only observe a single location in the sky at any given time, the multi-beam array will be able to point at seven locations simultaneously. It will, furthermore, observe them at a much higher degree of sensitivity than is possible with the current arrangement.
Dan Werthimer and his crew are not the only group looking forward to the installation of the new array. SETI@home is, in fact, part of a consortium of hundreds of researchers from around the world who are interested in conducting research using the multi-beam array. The other major groups in the consortium include astronomers interested in detecting pulsars, and researchers mapping the density of hydrogen in our galaxy and beyond. Together, the three groups constitute the ALFA consortium - short for the Arecibo L-band Feed Array.
The multi-beam array offers important advantages to all researchers in the consortium. A survey that can point at seven different locations at the same time will be far more efficient than one that has to visit each location in succession. The fact that each of the feeds has its own separate receiver also makes it possible for scientists to listen at different frequencies at same time - a feat that is not possible with a single feed.
Over the weekend of March 21-23 ALFA representatives met at Arecibo to coordinate their plans for using new array (the Stellar Countdown was scheduled to coincide with their meeting). Working together, ALFA researchers hope to be granted as many as 10,000 observing hours on the radio telescope, spread over 5 years.
"Getting this much observing time is only possible because the consortium represents so many researchers" said Werthimer. Furthermore, he explained, all this telescope time will not come at the expense of other astronomers vying for telescope time. This is because using the multi-beam array, members of the consortium will be able to conduct their research far more efficiently than before, and will not compete with other scientists for precious (and far less efficient) observing time. The end result, Werthimer says, is that all telescope users will have more time available to conduct their observations.
The multi-beam array is currently being built in Australia, where a similar 13 feed array is already installed on the 64 meter dish at the Parkes Observatory. It is expected to arrive at Arecibo in April, 2004, and installation, according to Werthimer, will take around 9 months. Once the observations get under way, perhaps early in 2005, the SETI@home sky survey will become more sensitive and comprehensive than ever before. It will be a new chapter in the search for extraterrestrial intelligence.