The quest for extraterrestrial life faces immense challenges, given the vastness of the universe and the significant distances between stars. The Search for Extraterrestrial Intelligence (SETI), a specialized branch of astronomy, seeks extraterrestrial intelligence through technosignatures, indicative of advanced technology.
Despite six decades of searching, no conclusive evidence has been found. Now, astrophysics Ph.D. candidate Owen Johnson and his colleagues at Trinity College Dublin are exploring previously untouched frequency ranges in the ongoing pursuit of extraterrestrial life.
Unveiling the Potential of Lower Frequencies
SETI assumes that extraterrestrial civilizations might employ technology akin to Earth's, such as cell phones and radar. As these technologies emit detectable radio signals, focusing on radio frequencies becomes a logical starting point in the search for extraterrestrial intelligence.
However, prior technosignature surveys have concentrated on frequencies above 600 MHz, neglecting lower frequencies utilized in common Earth communication services like air traffic control and FM radio.
Despite the potential of lower frequencies, their exploration is relatively recent due to the novelty of telescopes operating at these levels. Lower-frequency radio waves pose detection challenges due to their lower energy.
In a groundbreaking survey discussed in the paper, titled "A Simultaneous Dual-site Technosignature Search Using International LOFAR Stations" published in The Astrophysical Journal, the world's most sensitive low-frequency telescope called Low-Frequency Array (Lofar) scanned 44 exoplanets at 110 to 190 MHz using stations in Ireland and Sweden.
Lofar's advantage lies in its extensive coverage, observing 5.27 square degrees of the sky per telescope pointing and revealing over 1.6 million targets in total when considering neighboring stars and their planets.
Overcoming Earthly Challenges in the Search for Extraterrestrial Technosignatures
The pursuit of technosignatures from space encounters a major challenge-many of these signals are commonplace on Earth. This becomes problematic as the sensitive telescopes used in these searches can detect signals like phone calls from considerable distances within the solar system.
Consequently, the collected data is inundated with numerous Earth-origin signals, making it difficult to distinguish potential extraterrestrial signals and adding complexity to the search.
To address this, the team developed an innovative approach known as the "coincidence rejection" method. This method considers local radio emissions at each telescope station, only including signals in the dataset if they simultaneously appear at both stations.
Moreover, the approach significantly narrows down the candidate signals from thousands to zero, indicating that no signs of intelligent life were detected in our initial search. However, recognizing the success of the coincidence rejection method is crucial for future searches on the many Earth-like planets expected to be discovered.
Despite the current outcome, there are promising avenues for low-frequency technosignature searches. Another survey, Nenufar, is underway operating at 30-85 MHz, and additional Lofar observations will expand the survey's scope tenfold in the coming year. The data collected also serves multiple purposes, including the study of pulsars, fast radio bursts, radio exoplanets, and more.
As the team embarks on this lengthy journey, there is optimism that numerous discoveries await, with the ultimate reward being the potential identification of extraterrestrial life.
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