LET’S TALK ABOUT
LET’S TALK ABOUT...
SETI
BY CASSANDRA CAVALLARO (SKAO) In December, an intriguing radio signal was detected by the Parkes radio telescope in Australia, originating from around Alpha Centauri, the nearest star to our Solar System. ‘Intriguing’ because it fits the profile of signals sought by one particular community among astronomers: those engaged in the search for extra-terrestrial intelligence (SETI). “SETI attempts to answer the most profound question in science: Are we alone in the Universe? It’s also a question that humans have asked themselves since they first looked up at the night sky,” says Dr Steve Croft, a researcher at the Berkeley SETI Research Center and member of the SKA’s Cradle of Life Science Working Group. This topic is a favourite for sci-fi fans, and Hollywood has spent decades imagining just how we might one day interact with alien lifeforms, whether it was harmless little ET being accidentally stranded on Earth, Jodie Foster making contact through radio astronomy (and inspiring the name of this very magazine), or the USS Enterprise using warp speed to seek out new life and new civilisations. Sci-fi aside, there have been a couple of tantalising “maybes” in the real-life quest over the past 50 years. Let’s start with some background: SETI is concerned with intelligent life (rather than the building blocks of life discussed in the last issue of Contact) so the focus is on detecting signals from any alien technology. These signals are known as technosignatures. These could be messages being broadcast deliberately, or just the electromagnetic noise that technology creates which can leak out into space. This happens with our own technology too, so signals from our early radios, then TVs, radar, etc. here on Earth have been travelling further into space since they were first emitted.
It was in 1960 that modern SETI began in earnest with Dr Frank Drake’s Project Ozma, which used a 26m radio telescope at Green Bank Observatory in the United States to observe two stars, Tau Ceti and Epsilon Eridani. It was looking for unusual “blips” in signals around 1420 MHz, the frequency emitted by neutral hydrogen, the most abundant element in the Universe. The idea was that any smart civilisation would choose a frequency that others were likely to be scanning, and as 1420 MHz is so fundamental to studies of the Universe, this would be a good place to start looking. Nothing out of the ordinary was discovered by Project Ozma, but the search was on. A year later Dr Drake wrote what came to be known as the Drake Equation, outlining all the factors which would contribute to the probability of finding intelligent life elsewhere in our galaxy (see image). As science writer Dr Nadia Drake has pointed out, many of the variables were unknown at the time her father wrote the equation, but it continues to guide modern SETI as astronomers learn more and can fill in the blanks. That period also saw the first transmission sent from Earth into outer space with the sole purpose of reaching other civilisations – a controversial topic to this day – using the Arecibo radio telescope in Puerto Rico in 1974. Dr Drake designed a message which included depictions of our number system, the human form and Arecibo itself. Read more about it here.
Above: SETI is the search for intelligent life elsewhere in the Universe. 14
