The Search For Extraterrestrial Life

Carol explores the origins and new developments in the search for intelligent life forms outside planet Earth.

Radio Telescope view at night with milky way in the sky.


For those keeping an eye on the stars, and with an interest in extraterrestrial life, the past few months have been exciting ones. Last July saw the announcement of a 100 million US dollar search for intelligent life in space. This was followed days later by the announcement that an Earth-like planet had been found around a sun-like star. Then in September liquid water was found on Mars, and in October gaseous molecular oxygen was found streaming out of a comet.

Recent developments

London’s Royal Society was the backdrop for the July announcement, led by Stephen Hawking, of a new ten-year endeavour, named Breakthrough Listen, to search for signs of intelligent life in space. The project aims to survey the one million closest stars to Earth, as well as one hundred other nearby galaxies. The Project is being entirely financed by Yuri Milner, a Russian venture capitalist who made his billions by investing in Facebook, Twitter and other such online enterprises. Milner has a long connection to space; he is a theoretical physics graduate of Moscow State University and was born in 1961, the year the man he is named after, Yuri Gargarin, became the first man in space. Despite the obvious excitement surrounding the launch, Milner was careful not to hype up the project, conceding that “It’s quite likely that we won’t find anything.” The Breakthrough Listen launch was followed just three days later by the announcement that NASA’s Kepler mission, which aims to detect small planets orbiting distant stars, had done exactly that, and found the first near-Earth-sized planet in the so-called ‘habitable-zone’ around a sun-like star. The newly discovered planet, Kepler-452b, is older than Earth, is 60 percent larger in diameter, has much stronger surface gravity, and has a good chance of being rocky (as opposed to being entirely gaseous or liquid). It has a 385-day orbit around a star of a similar type to our own sun. It is within our own Galaxy, the Milky Way, and is approximately 1,400 light years away. The fact that it is older than Earth, means there has been a significant amount of time for life to arise. John Grunsfeld, the associate administrator of NASA’s Science Mission Directorate, declared that the discovery “brings us one step closer to finding an Earth 2.0.” In September, another NASA announcement brought us the news that liquid water had been found on Mars. The trickling water is salty and seasonal, only appearing in warmer weather. Although it’s not known exactly where it comes from, we do know there is buried ice on Mars, so it is possibly melt-water. Alternatively, it could be that the salt absorbs water vapour from the atmosphere. The water is potentially capable of sustaining life, but it may be just too salty. In October, the European Space Agency’s Rosetta spacecraft discovered that gaseous molecular oxygen, O2, was being pumped out by a comet. Although oxygen is highly abundant in the universe, it’s also highly reactive and rare to find in space as molecules of O2. Here on Earth we have plants to continuously top up our supplies. Although there are many ways to produce oxygen that don’t involve life, O2 still tops the list of so-called ‘biosignatures’ that could indicate the presence of life. And then came the curious case of a star called KIC 8462852, which emits an unusual light pattern. Its brightness dips irregularly, in a manner that would suggest it is being circled or surrounded by something. It’s not a planet and a cluster of comets has been ruled out, and some are still excited about the possibility of an ‘alien megastructure’.

When did the search for extraterrestrial life begin?

There is no doubt that people have been staring at the skies for centuries, pondering life’s deepest questions. The issue of whether we are alone in the cosmos may well have been a persistent fascination, but it wasn’t until the dawning of the space age in 1957, with the launch of Russia’s Sputnik, the first artificial satellite, that the discussion took on a more serious tone, and people began to think about credible methods of communication. In 1959 two physicists from Cornell University, Cocconi and Morrison, published a seminal paper in the influential journal Nature entitled “Searching for Interstellar Communications”. Here they pondered that in assuming intelligent life on other planets had actually arose, then how would they attempt to communicate with us? They decided that sending out electromagnetic radiation would be a legitimate option, and even discussed possible wavelengths for the transmission.

What exactly are we looking for?

Here on Earth, many of our technological inventions, such as televisions and radios, emit electromagnetic radiation. We could tell that these signals come from an artificial source because the signals are of a repetitive nature and within a narrow bandwidth. These are exactly the kind of artificial signals we can look for coming in towards Earth from outer space. Radio telescopes with large radio antennas are used to pick up such signals, radio waves being particularly efficient at penetrating the Earth’s atmosphere. The Breakthrough Listen project will involve the use of two major radio telescopes in West Virginia and Australia, while a third telescope in California will search for optical laser emissions from technological sources, across the electromagnetic spectrum from near infrared through visible light to near ultra-violet.

What are we likely to find?

If we do ever find life in space, it may indeed come in the form of intelligent beings sending out radio waves. But it’s more likely to come in the form of microbes, or so-called extremophiles: organisms with the ability to thrive in extreme environments that would be inhospitable to other forms of life. They exist on Earth in places such as inside a volcano, in the desert and on top of the Himalayas. These would be the sort of organisms we might find in the salty water on Mars.

Where are we likely to find it?

In order to figure out where we are likely to find life, we first need to ask what is needed to support life. And the key to this question is water. Water is an absolutely critical component for life (well, at least for life as we know it). Having liquid water on the surface of a planet requires it to be at just the right temperature, which means it has to be at just the right distance from its star. A planet sitting in this ‘Habitable zone’ is said to have the potential to support life. Some have even taken to referring to this zone as the ‘Goldilocks Zone’ – not too hot, not too cold, but just right. Where exactly this zone occurs depends on factors such as the size and energy output of the star; hotter stars will have their habitable zone further away from them.

What have we found so far and what does the future hold?

Although signs of intelligent extraterrestrial life may have escaped us thus far, we have managed to confirm approximately a dozen Earth-size planets situated within habitable zones. 2015 was an exciting year, and this year promises more cutting edge research in the field as well as the beginning of Breakthrough Listen’s search. Until we find an earth-like exoplanet showing signs of life that we can point our radio telescopes at, the search for habitable distant worlds continues.