NASA's
High
Resolution
Microwave
Survey

Targeted Search and Sky Survey Status
Quarterly Report -- March 1993

BACKGROUND

The High Resolution Microwave Survey (HRMS) is part of the Toward Other Planetary Systems (TOPS) program in NASA's Solar System Exploration Division. The HRMS looks for evidence of planets orbiting other stars through radio emissions that may be produced by technological civilizations on any such planets. The HRMS has two search modes, a Sky Survey and a Targeted Search. The Sky Survey, managed by the Jet Propulsion Laboratory, uses 34-meter antennas in NASA's Deep Space Network to sweep the entire sky over a wide range of frequencies for the presence of strong signals. The Targeted Search uses the largest available radio telescopes to observe nearby Sun-like stars over a narrower range of frequencies for weak signals. The Targeted Search is managed by NASA's Ames Research Center, which is also the lead center for the HRMS. The combination of the two search modes is millions of times more comprehensive than the sum of all previous search programs. The observational phase of the HRMS was inaugurated at 1900 hours Universal Time on 12 October 1992 at the NASA Goldstone Deep Space Communications Complex in California and the Arecibo Observatory in Puerto Rico. The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, operated by Cornell University for the National Science Foundation. In a coordinated program, the Arecibo antenna pointed at the star Gliese 615.1A and the Goldstone antenna began to scan a small area of sky that included the position of the target star. The beginning of the search generated worldwide interest in the media. This report presents an overview of the observations and results to date.

THE OBSERVATIONS

Sky Survey

Initial observations began with the new 34-meter antenna at the Venus Development Station at Goldstone. The project is using the available X-Band receiver which can be tuned from 8200 to 8600 MHz, and the Sky Survey Prototype System (SSPS). The SSPS divides a single polarization 40 MHz band into two million 20 Hz channels and automatically looks for continuous wave signals as the search progresses. Each observation involves driving the antenna rapidly in a precise "sliding racetrack" pattern programmed to cover a "sky frame," a rectangular area of sky approximately 1.8 degrees high and 30 degrees wide. While observing, the SSPS temporarily stores data from channels with power exceeding a specified threshold level and excises data from channels affected by terrestrial signals. The scan pattern is designed so that each point in the frame will be scanned by the antenna at least twice (with slightly different position offsets) at times separated by about eight minutes. At the completion of the sky frame, the stored data are analyzed and candidate signals are selected for immediate verification tests.

Twenty-five sky frames, including four repeat frames, have been observed at X-Band. To date, no candidates have passed the verification tests and the results are entirely consistent with the expected thermal noise statistics. The SSPS is now observing about 32 hours per week on the 34-meter antenna with an increase in allocated time scheduled for later in the year. At other times, the SPSS is completing a series of special observations on the adjacent 26-meter antenna using an available L-Band receiver. These observations are designed to optimize radio astronomy data and improve interference excision algorithms. Three 5 degree by 30 degree sections of the galactic plane are being observed repeatedly in frequency bands that include the natural emission lines produced by hydrogen atoms and hydroxyl radicals (OH). Results of these observations, including maps of the detected emission, will be published later this year.

Work also continues at JPL on developing the Sky Survey Operational System (with sixteen times the bandwidth of the SSPS) and the RF Systems to be used by both search modes.

Targeted Search

The Targeted Search System (TSS) used the Arecibo 305-meter antenna, the world's largest, for its initial observations. The TSS processed a dual polarization 10 MHz bandwidth into more than 14 million, 1 Hz wide, simultaneous channels. In parallel, it also produced channel resolutions of 7 Hz and 28 Hz. Data were analyzed in real-time for the presence of continuous wave and pulsed signals that may drift in frequency by as much as 1 Hz per second. Twenty-five stars within 100 light years were observed. Receivers provided by the observatory allowed observations in four frequency bands covering a total of about 300 MHz within the range from 1300 MHz to 2400 MHz.

Each "observation" of a star in a particular frequency band consisted of three steps with the antenna first pointed at the star, then away from the star, and then back at the star. Each step lasted either 92 seconds or 299 seconds. Signals that were present only when the telescope was pointed at the star (and not previously seen in other observations) were considered to be of possible extraterrestrial origin and were subjected to further tests. Signals that were present both "on" and "off" the star were deemed to be terrestrial interference signals. A total of 436 observations were conducted during the 200 hours of assigned telescope time. A large number of interference signals were detected and cataloged. Fifteen signals required further verification tests, but all proved to be intermittent terrestrial signals. Analysis of the data collected at Arecibo continues with the goal of developing better techniques for quickly identifying, classifying, and perhaps even avoiding interference signals.

Since returning from Arecibo, the TSS has been reassembled in the development lab at NASA Ames. As expected, operational experience has indicated the need for modifications to several circuit boards and improvements to the software. While those modifications are under way, the capability of the system is being doubled to process 20 MHz of bandwidth. The increased capability is needed for observations of nearby Sun-like stars in the Southern Hemisphere, scheduled to begin in 1994 at the 64-meter antenna of the Parkes Observatory in Australia. Parkes is part of the Australian Telescope National Facility operated by the Commonwealth Scientific Industrial Research Organization. A Memorandum of Agreement has been negotiated between NASA and CSIRO through the Australian Space Office for the use of this facility.

RESULTS

No signals from beyond our Solar System have been detected yet. Although many signals have been detected, none appears to originate from a fixed point on the celestial sphere. Most of the signals were recognized immediately as terrestrial interference by the software. A few signals required verification tests but no signal passed this level of testing. In summary, the HRMS has successfully inaugurated its observational phase. Both the Targeted Search and the Sky Survey are using the lessons learned in the initial observations to improve their hardware, software, and observation techniques as they build additional systems to implement the ten year search.

Other Information

SETI Institute - 2035 Landings Drive - Mountain View, CA (415) 961-6633