We report radio SETI observations on a large number of known exoplanets and other nearby star systems using the Allen Telescope Array (ATA). Observations were made over about 19000 hours from May 2009 to Dec 2015. This search focused on narrow-band radio signals from a set totaling 9293 stars, including 2015 exoplanet stars and Kepler objects of interest and an additional 65 whose planets may be close to their Habitable Zone. The ATA observations were made using multiple synthesized beams and an anticoincidence filter to help identify terrestrial radio interference. Stars were observed over frequencies from 1-9 GHz in multiple bands that avoid strong terrestrial communication frequencies. Data were processed in near-real time for narrow-band (0.7-100 Hz) continuous and pulsed signals, with transmitter/receiver relative accelerations from -0.3 to 0.3 m/s 2 . A total of 1.9 x 10 8 unique signals requiring immediate follow-up were detected in observations covering more than 8 x 10 6 star-MHz. We detected no persistent signals from extraterrestrial technology exceeding our frequency-dependent sensitivity threshold of 180 -310 10 -26 W m -2 .

We present results from an initial survey of the 2(12)-1(11) transition of formaldehyde (H2CO) at 140.8 GHz in giant molecular clouds in the far outer Galaxy (RG >or= 16 kpc). Formaldehyde is a key prebiotic molecule that likely plays an important role in the development of amino acids. Determining the outermost extent of the H2CO distribution can constrain the outer limit of the Galactic Habitable Zone, the region where conditions for the formation of life are thought to be most favorable. We surveyed 69 molecular clouds in the outer Galaxy, ranging from 12 to 23.5 kpc in galactocentric radius. Formaldehyde emission at 140.8 GHz was detected in 65% of the clouds. The H2CO spectral line was detected in 26 of the clouds with RG > 16 kpc (detection rate of 59%), including 6 clouds with RG > 20 kpc (detection rate of 55%). Formaldehyde is readily found in the far outer Galaxy-even beyond the edge of the old stellar disk. Determining the relatively widespread distribution of H2CO in the far outer Galaxy is a first step in establishing how favorable an environment this vast region of the Galaxy may be toward the formation of life.

Recently, Lattelais et al. have interpreted aggregated observations of molecular isomers to suggest that there exists a "minimum energy principle," such that molecular formation will favor more stable molecular isomers for thermodynamic reasons. To test the predictive power of this principle, we have fully characterized the spectra of the three isomers of C 3 H 2 O toward the well-known molecular region Sgr B2(N). Evidence for the detection of the isomers cyclopropenone (c-C 3 H 2 O) and propynal (HCCCHO) is presented, along with evidence for the non-detection of the lowest zero-point energy isomer, propadienone (CH 2 CCO). We interpret these observations as evidence that chemical formation pathways, which may be under kinetic control, have a more pronounced effect on final isomer abundances than thermodynamic effects such as the minimum energy principle.

The Allen Telescope Array (ATA) is a cm-wave interferometer in California, comprising 42 antenna elements with 6-m diameter dishes. We characterize the antenna optical accuracy using two-antenna interferometry and radio holography. The distortion of each telescope relative to the average is small, with RMS differences of 1% of beam peak value. Holography provides images of dish illumination, characterizing as-built mirror surfaces. Maximal distortions across 2 meter lengths appear to result from mounting stresses or solar radiation. Experimental RMS errors are 0.7 mm at night and 3 mm under worst-case solar illumination. For frequencies 4, 10, and 15 GHz, the nighttime values indicate sensitivity losses of 1, 10 and 20%, respectively. ATA's wide-bandwidth receiver permits observations over a continuous range 0.5-11.2 GHz. We probe the antenna optical gain and beam pattern stability as a function of focus position and observation frequency, concluding that ATA can produce high fidelity images over a decade of simultaneous observation frequencies. We quantify solar heating effects on antenna sensitivity and pointing accuracy. We find that during the day, observations 5 GHz will suffer some sensitivity loss and it may be necessary to make antenna pointing corrections on a 1-2 hourly basis.Index Terms-Allen telescope array (ATA), antenna radiation patterns, digital holography, dish surface accuracy, image reconstruction, radio astronomy, radio telescope, square kilometer array. Manuscript

The 1959 Nature article by Giuseppe Cocconi and Phil Morrison 1 provided the theoretical underpinnings for SETI, accompanied in 1960 by Project Ozma 2 , the first radio search for signals by Frank Drake at the National Radio Astronomy Observatory (NRAO). Well over 100 search programs have been conducted since that time, primarily at radio and optical wavelengths, (see www.seti.org/searcharchives) without any successful signal detection. Some have suggested that this means humans are alone in the cosmos. But that is far too strong a conclusion to draw from far too small an observational sampling. Instead of concluding that intelligent life on Earth is unique, it is more appropriate to note that in 50 years our ability to search for electromagnetic signals has improved by at least 14 orders of magnitude and that these improvements are still occurring at an exponential rate. At the SETI Institute we are in the process of reinventing the way we search in order to fully utilize these technological enhancements. We are now building the setiQuest community and we intend to get the world involved in making our searches better. We need to find ways to harness the intelligence of all Earthlings in order to better seek out extraterrestrial intelligence. If we do it right, we just might succeed, and we might also change how we see ourselves, and make our own world a better place.