Search for intelligent aliens explores new radio-frequency realms

A view of the LOFAR station at Birr Castle in Ireland, which has been listening for alien radio signals.
A view of the LOFAR station at Birr Castle in Ireland, which has been listening for alien radio signals. (Image credit: I-LOFAR)

A new European search for extraterrestrial radio signals at low, uncharted frequencies is underway, having already listened to over 1.6 million star systems.

SETI, the search for extraterrestrial intelligence, has traditionally focused on radio frequencies higher than a gigahertz, such as the hydrogen-line frequency at 1.42 GHz. SETI astronomers tend to shy away from lower frequencies because Earth's atmosphere renders observations noisy.

However, Europe's Low Frequency Array, or LOFAR for short, is specially designed to conduct radio astronomy at these very frequencies. 

Related: The search for alien life (reference) 

LOFAR is an array of radio antennas that span hundreds of kilometers across Europe, centered in the Netherlands but with additional stations in France, Germany, Ireland, Latvia, Poland, Sweden and the United Kingdom. The stations incorporate two types of antenna: low band antennas that operate between 10 and 90 MHz, and high band antennas that listen to the universe between 100 and 250 MHz.

In conjunction with the Breakthrough Listen SETI project, the LOFAR stations in Ireland and Sweden have been used in conjunction with one another in the first part of Breakthrough Listen's first-ever low-frequency search.

This search used the high band antennas to listen for radio signals at frequencies of between 110 and 190 MHz. Primarily, the search is looking for leakage from high-power transmitters, such as planetary radar or communications with spacecraft. The search encompassed 1,631,198 target star systems identified by NASA's Transiting Exoplanet Survey Satellite (TESS) and the European Space Agency's Gaia astrometric probe.

By using multiple sites in Ireland and Sweden, astronomers were able to negate the effects of radio-frequency interference and quickly rule out any false positives. For example, if an anomalous signal were only spotted by one station and not the others, it would be local interference. Only a signal coming from space could be detected by all the stations.

No narrowband radio signals with a distinctive frequency drift caused by the orbital motion of an exoplanet hosting a transmitter beaming out signals with a power of at least tens of millions of watts were detected. However, the low-frequency search is only just beginning, and improvements in coming years will increase its sensitivity. 

"LOFAR is soon to undergo a staged series of upgrades across all stations in the array across Europe, which will allow an even broader SETI at ranges of 15-240MHz," said graduate student Owen Johnson of Trinity College Dublin, who is the lead author of a new paper describing the results, in a statement

Among these upgrades will be two new LOFAR stations in Bulgaria and Italy. Computing software and artificial-intelligence algorithms will also speed up the analysis of the results.

"We have billions of star systems to explore and will be relying on some machine-learning techniques to sift through the immense volume of data," said Johnson. "That in itself is interesting — it would be fairly ironic if humankind discovered alien life by using artificial intelligence." 

The first results from the LOFAR SETI search were published on Oct. 24 in The Astronomical Journal.

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Keith Cooper
Contributing writer

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.

  • rod
    From the paper cited,
    "In this survey at 110–190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported."

    The NASA exoplanet archive site shows 4125 distinct star names listed for the known stars with exoplanets,
    Did all 4125 stars in the list get scanned for ET phoning home? Those stars show 5535 exoplanets confirmed now. 398 TESS exoplanets are confirmed at the NASA site.
  • rod
    The 398 confirmed TESS exoplanets show 309 unique star names.

    Edit. The reference paper does state about TESS list, "We report observations toward 44 unique targets from the TESS catalog in this study, where each target was observed for 15 minutes. Figure 1 shows the distribution of these targets observed in comparison to the pool of all TESS TOIs."
  • rod
    Also from the paper, "2. Observations This study encompasses a total of 44 targeted pointings, where each pointing consists of a 15 minute scan centered on specific targets selected from the TESS catalog, focusing on confirmed or candidate exoplanets (refer to Figure 1). The entire observation campaign spanned a duration of 11 hr, covering an area of 232 deg2 in the northern sky."
  • rod
    My thoughts. Surveys like this *look important* when some folks claim UFO/UAPs are coming from other star systems to visit Earth. Apparently, no confirmation that ET is buzzing Earth or beaming out messages across space from other star systems is established presently.
  • Classical Motion
    Have they found many signals in space with those frequencies? I always thought those frequencies would be few and weak. It appears that space is so large, that for EM communication, one is going to need a lot of power. Nature does this by using multiple emitters and emitting a flux. The flux can superposition and acquire the intensity and power needed.

    But for lower frequencies, much larger collective structures for the proper wavelength are needed. How large of a structure do you think a plasma will allow.....and for how long?

    To call it a radio signal the F must be constant and have repeatable duration. Otherwise, it's just static.

    Static is all the superposition of EM, at point of detection. Or at any point in space.

    All radio emissions should be much weaker then any light source. Organized structure with the dimension needed would be rare, in my opinion.

    But if I had a low frequency receiver array on the far side of moon, I might be pleasantly surprised.
  • Dave
    Intelligent lifeforms observing the earth do not wish contact. They do not want to be discovered. They would not use a frequency or a form of communication we could understand. Our science is primitive in comparison.