[Paper Review] The SERENDIP III 70 cm Search for Extraterrestrial Intelligence

Stuart Bowyer, M. Lampton+4 more|arXiv (Cornell University)|Jul 2, 2016

Radio Astronomy Observations and Technology3 citations

TL;DR

This paper presents a four-year sky survey using the SERENDIP III system at the Arecibo Telescope to search for narrowband radio signals from extraterrestrial intelligence. Despite analyzing over 10^14 data points and detecting numerous candidate signals, no evidence of artificial signals was found; the peak power distributions were consistent with random noise, and upper limits on isotropic equivalent flux were established for nearby G-dwarf stars.

ABSTRACT

We employed the SERENDIP III system with the Arecibo radio telescope to search for possible artificial extraterrestrial signals. Over the four years of this search we covered 93% of the sky observable at Arecibo at least once and 44% of the sky five times or more with a sensitivity of ~3E-25 W/m2. The data were sent to a 4 million channel spectrum analyzer. Information was obtained from over 1E+14 independent data points and the results were then analyzed via a suite of pattern detection algorithms to identify narrow band spectral power peaks that were not readily identifiable as the product of human activity. We separately selected data coincident with interesting nearby G dwarf stars that were encountered by chance in our sky survey for suggestions of excess power peaks. The peak power distributions in both these data sets were consistent with random noise. We report upper limits on possible signals from the stars investigated and provide examples of the most interesting candidates identified in the sky survey. This paper was intended for publication in 2000 and is presented here without change from the version submitted to ApJS in 2000.

Motivation & Objective

• To conduct a non-intrusive, wide-area sky survey for artificial narrowband radio signals using the Arecibo Telescope.
• To detect potential extraterrestrial intelligence (ETI) signals by leveraging existing astronomical observing time.
• To investigate signals coinciding with nearby G-dwarf stars, which are considered prime targets for ETI life.
• To apply advanced RFI rejection and pattern detection algorithms to distinguish artificial from terrestrial signals.
• To establish conservative upper limits on isotropic equivalent flux for stars in the CFA G-dwarf list observable from Arecibo.

Proposed method

• Utilized SERENDIP III's 4×10⁶ channel spectrum analyzer with 1.7-second integration and 0.6 Hz resolution to process 12 MHz bandwidth at 430 MHz.
• Applied adaptive thresholding by identifying channels exceeding 16× the local mean power after baseline smoothing over 8,000 channels.
• Employed real-time power spectrum generation and off-line data reduction including RFI filtering and position-based signal validation.
• Used Gaussian beam fitting (Algorithm 3) to assess signal morphology and distinguish from terrestrial interference.
• Conducted targeted analysis on 494 G-dwarf stars visible from Arecibo, using Hipparcos distances to compute upper limits on source luminosity.
• Applied statistical analysis to peak power distributions to test for non-random excesses beyond noise expectations.

Experimental results

Research questions

• RQ1 Are there narrowband radio signals in the sky that are not attributable to human-made RFI?
• RQ2 Do any signals coincide with nearby G-dwarf stars, suggesting intentional transmission?
• RQ3 Can the SERENDIP III system detect artificial signals at sensitivities of ~3×10⁻²⁵ W/m² across a wide sky area?
• RQ4 Is the distribution of detected power peaks consistent with random noise, or does it indicate artificial sources?
• RQ5 What are the upper limits on isotropic equivalent flux for nearby G-dwarf stars based on non-detection?

Key findings

• The SERENDIP III survey covered 93% of the Arecibo-visible sky at least once and 44% five or more times, with a sensitivity of ~3×10⁻²⁵ W/m².
• No narrowband signals were identified as extraterrestrial; all peak power distributions were consistent with random noise.
• Among 494 observed G-dwarf stars, 439 were observed multiple times, and no excess power was detected beyond noise levels.
• Upper limits on isotropic equivalent flux were derived for stars in the CFA G-dwarf list, with sensitivity uncertain by a factor of two due to beam pattern averaging.
• The most notable candidate signal had a Gaussian fit score of 79.371, but was not confirmed as artificial and was likely RFI.
• The study confirms the viability of non-intrusive, collateral SETI data collection using major observatories without dedicated telescope time.