Is there life beyond Earth? The question has proven to be one of the most difficult to answer in science. Despite the seemingly limitless vastness of the universe, implying the potential for abundant life, the vast distances between stars make the search akin to finding a needle in a cosmic haystack.
The Search for Extraterrestrial Intelligence (Seti) is a branch of astronomy dedicated to finding extraterrestrial life by looking for unusual signals called technosignatures.
The identification of a technosignature would not only signify the existence of life, but specifically indicate the presence of intelligent life using advanced technology.
That said, 60 years of searching has so far come up short. But now my colleagues and I have begun exploring a previously unexplored frequency range.
Seti assumes that alien civilizations may rely on technology in a similar way to humans on Earth, such as the use of mobile phones, satellites or radar.
Because a significant portion of such technology generates signals that are clearly observable in radio frequencies, focusing on these wavelengths serves as a logical starting point in the search for potential extraterrestrial intelligence.
Previous technosignature studies have only examined the radio frequency band above 600 MHz, leaving lower frequencies virtually unexplored. That’s despite the fact that everyday communications services like air traffic control, marine distress broadcasts and FM radio stations all emit this type of low-frequency radiation onto Earth.
The reason this has not yet been investigated is that telescopes that operate at these frequencies are quite new. And lower frequency radio waves have less energy, which means they are harder to detect.
In our completed research we ventured into these frequencies for the first time.
The Low Frequency Array (Lofar) is the world’s most sensitive low-frequency telescope, operating from 10-250 MHz. It consists of 52 radio telescopes and more are on the way, spread across Europe. These telescopes can achieve high resolution when used simultaneously.
However, our study only used two of these stations: one in Birr, Ireland, and the other in Onsala, Sweden. We examined 44 planets orbiting stars other than our Sun that had been identified by NASA’s Transiting Exoplanet Survey Satellite. Over two summers we scanned these planets with our two telescopes at 110 to 190 MHz.
At first this does not seem like a large number of targets, but low-frequency observation has a major advantage because they have a large field of view compared to their high-frequency siblings. This is because the area of the sky covered decreases as frequencies increase.
In the case of Lofar, we covered 5.27 square degrees of the sky with each aim of our telescopes. This culminated in 36,000 targets per target point – or more than 1,600,000 targets in total, if you consider what other stars are nearby and also count their planets.
Disturbing signals
Searching for technosignatures from space poses a significant challenge: the same technosignatures are ubiquitous on Earth. This poses an obstacle because the telescopes in these searches have sensitivity levels that can detect signals, such as a telephone call, halfway across the solar system.
As a result, the collected data is swamped with thousands of signals originating from Earth, creating significant difficulty in isolating and identifying signals that could be of extraterrestrial origin. The need to search this extensive and noisy data set adds a layer of complexity to the search.
We have devised an innovative approach to reduce such radio frequency interference, the so-called ‘random rejection’ method. This takes into account the local radio emissions from each of our telescopes.
For example, if I use the phone close to the telescope in Ireland to call my supervisor, that same call in Sweden will not show up in the data, and vice versa (especially since the telescope is not pointing in our direction, but pointing at a candidate exoplanet) . Therefore, we decided to include signatures in the dataset only if they were simultaneously present at both stations, indicating that they come from outside Earth.
In this way we have reduced thousands of candidate signals to zero. This means that we haven’t found any sign of intelligent life in our search, but we’re just getting started – and there are likely to be a huge number of Earth-like planets. Knowing that the chance rejection method works with a high success rate could be crucial in helping us discover life on one of these planets in the future.
There are many ways to look for technosignatures at low frequencies. A sister study (Nenufar) is currently being conducted that operates on 30-85 MHz.
In addition, further Lofar observations will increase the size of the survey by a factor of ten over the course of the next year. The data collected is also used to investigate astronomical objects known as pulsars, fast radio bursts, radio exoplanets and more.
Fortunately, we are only at the beginning of a long journey. I have no doubt that many wonderful things will be found. And if we’re lucky, we may reap the greatest reward of all: companionship in the cosmos.
Owen Johnson, PhD candidate in astrophysics, Trinity College Dublin
This article is republished from The conversation under a Creative Commons license. Read the original article.
