Possibility of Intelligent Life Elsewhere in the Universe

This document is a 1977 revised report prepared by the Congressional Research Service for the U.S. House of Representatives Committee on Science and Technology. It provides a comprehensive overview of the scientific search for intelligent life elsewhere in the universe. The report begins by addressing life within our own solar system, noting that while Mars has been a primary target for biological probes like Viking 1 and 2, current scientific consensus suggests that if life exists elsewhere in our solar system, it is likely simple and non-intelligent. The report then shifts to the broader search for advanced civilizations, detailing the Drake Equation as a tool for estimating the number of such civilizations in the Milky Way. It discusses various methods for contact, categorizing them into electromagnetic signals (radio and laser) and space-based probes (manned or unmanned). The document highlights the transition from the term CETI (Communication with Extraterrestrial Intelligence) to SETI (Search for Extraterrestrial Intelligence), emphasizing a shift in focus toward signal detection rather than immediate two-way communication. Significant attention is given to the technical challenges of such a search, particularly the issue of radio frequency interference (RFI) and the need for international cooperation through the International Telecommunications Union (ITU) to protect specific frequency bands, such as the 'waterhole' region. The report also includes appendices detailing the conclusions of NASA's Interstellar Communication Study Group, the Soviet CETI program, and the contents of the Voyager 1 and 2 records. Notably, the introduction explicitly clarifies that this report does not discuss Unidentified Flying Objects (UFOs), distinguishing the scientific search for extraterrestrial intelligence from the study of UFOs.