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The Cradle of Life: A Cosmic Search for Ourselves

proto-planetary disk of dust and gas swirling around a newly formed star

Artist’s conception of a proto-planetary disk of dust and gas swirling around a newly formed star, beginning the process of coalescence into planets. Credit: University of Copenhagen/Lars Buchhave

By Carol Oliver & Ian Morrison

The SKA will have an unprecedented capability to listen for traces of any advanced civilisations within 1000 light years of Earth, which encompasses hundreds of thousands of solar systems.

One of the most profound questions we can ask of ourselves is: “Are we alone in the universe?” It is also a tremendously difficult question to answer, but as new instruments emerge our knowledge is increasing exponentially towards a tantalisingly common theme – we live in a universe made for life.

This question has many layers, like an onion. The slow peeling back of the early layers reveals new views of the universe and new questions about our understanding of it. While we could be alone in the stupendous immensity of the universe, we also might not be. Either way, the question confronts our thinking about who we are, where we came from and the ultimate meaning of life.

The Square Kilometre Array will eventually be around 50 times more sensitive than any current radio telescope on Earth, with capabilities that could help to answer some of the age-old puzzles about life in the universe and our place in it. Radio telescopes are where the Search for Extraterrestrial Intelligence (SETI) began, and where it has expanded into the quest to understand the context in which we make that search. If the rules of physics and chemistry are the same all over the universe, then does that also apply to the rules of biology across space and time?

If it turns out that the rules of biology are universal then, since our own solar system is only around one-third of the age of the universe, it suggests that there may be other solar systems with the technological civilisations sought by SETI. We currently have no basis for estimating the probability of extraterrestrial civilisations; we have not even found a single simple microbe outside of the biosphere of Earth. However, over the past century our ability to seek out the evidence required to make that estimate has increased.

Our ability to search for evidence of life will take a dramatic step forward with the Square Kilometre Array (SKA), which will be the watering hole where astrophysics meets astro­biology to discuss the key questions about life in the universe.

  • How do stars and planets form?
  • What are the magnetic fields around these planets?
  • How do these planets attain the ingredients for life and maintain conditions for life to thrive and diversify?
  • Is there microbial life elsewhere?
  • Has the evolution to complex life, including intelligence and technological civilisations, already taken place on other worlds elsewhere in our galaxy or beyond?

The SKA will be able to image nearby stellar nurseries, and locate proto-planetary disks of the kind from which our own solar system formed around five billion years ago. Within

1000 light years of Earth there may be hundreds or more of these solar-systems-in-the-making, and the high sensitivity and resolution of the SKA will allow astronomers to study these systems in unprecedented detail.

There is the potential to learn how planets and moons form in the star’s “habitable zone”, where liquid water can exist and where it is neither too cold to be all frozen nor too hot to remain liquid. The SKA will be ideally suited to imaging the thermal radio emission from pebble-sized particles in the habitable zone, mapping the precise regions where smaller dust particles begin to coalesce into planets that have the potential to support life, including small rocky planets like Earth.

The higher end of the SKA’s observing frequency band will be sensitive to spectral emission lines from organic molecules such as amino acids, and its high resolution will enable us to trace the journey of these molecules from the interstellar medium to the outer regions of proto-planetary disks, where they may be incorporated into comets that later deliver them to the inner planets (and possibly moons) that are warmer and potentially wetter. Such discoveries would support the hypothesis that life exists elsewhere in the universe.

We already know that the two key constituents for life as we know it – organic carbon for making a steady framework for life, and water as a solvent – are everywhere we look in the universe. On Mars, the Curiosity rover has found evidence of ancient organic carbon and an environment that would have been habitable by simple life in the past, placing another potentially pre-biological piece into the grand puzzle of the origin of life on Earth and in the universe.

Other trails of cosmic crumbs increase our confidence that the rules of biology may be as universal as those of physics and chemistry. For example, in 2011 Prof Sun Kwok and Dr Yong Zhang of The University of Hong Kong demonstrated that complex organic chemicals of the type found in oil and coal are present in the interstellar medium, and that stars routinely cook up this complexity.

And earlier this year astronomers using the Atacama Large Millimetre/Submillimetre Array discovered organic chemicals in a proto-planetary disk. They found that a young million-year-old star, MWC 480, about twice the mass of the Sun and 455 light years away, is brimming with methyl cyanide and its simpler cousin, hydrogen cyanide. These prebiotic molecules are in an area of the disk that equates to where our prebiotic molecule-bearing comets reside in our own solar system – the Kuiper Belt beyond Neptune. The lead author of the MWC 480 paper in Nature, Dr Karin Oberg, said: “Now we know we’re not unique in organic chemistry. Once more, we have learned that we’re not special. From a life in the universe point of view, this is great news.”

The discovery of the building blocks of life elsewhere in the universe adds colour and depth to our understanding of how life arose on Earth and possibly elsewhere. At the other end of the spectrum, SETI searches for direct evidence to support the conclusion that we are not alone in the universe.

More than half a century ago, dreams of understanding whether the rules of biology are universal were rudimentary. In 1960 Frank Drake wrote an agenda for the first scientific meeting focused on SETI, which included a shopping list of things that would need to be determined in order to estimate the number of communicating civilisations elsewhere in our galaxy. This list came to be known as the Drake Equation, which is a bit of a misnomer because it was intended as a logical but very basic agenda and remains today as an overlay for the wider goals of astrobiology.

At Drake’s meeting in 1960, the problem was expressed in terms of planets and their capability to support simple single-celled life, and the fraction of those planets that may go on to support complex life and eventually intelligence with similar capabilities to our own, such as a curiosity about the universe and the limbs required to experiment and eventually invent devices that transmit radio signals.

The SKA will have an unprecedented capability to listen for traces of any advanced technological civilisations that may be in our cosmic neighbourhood or beyond. On Earth, our technological activities give rise to powerful radio emissions that “leak” into space, including TV and radio broadcasts and pulses emitted by air traffic control radars. If an extraterrestrial civilisation employed similar radar technology, its signature could potentially be detected by the SKA from up to 1000 light years away – a range that includes hundreds of thousands of stars. Even TV- and radio-like signals will be detectable with the SKA from a few of our nearest-neighbour stars.

This capability may give us pause to think. Silence would suggest that intelligent life is rare or non-existent in any given time frame. A cacophony could change our view of our place in the universe.

The torrents of raw astronomical data coming from the SKA will be spectacular – enough to fill more than 140,000 DVDs every second. One of the great challenges is to process and reduce this data as much as possible in real-time so that data storage systems are not rapidly overwhelmed. Together with the primary scientific purpose of the data there can be a second use, which is to comb through the data for evidence that we are not alone in the universe.

The search will be broader and have far greater sensitivity than is currently available, with a tenfold greater range than any current radio telescope. Not only could the SKA detect leakage radiation from worlds ten times further away, but it also offers the tantalising possibility of detecting a deliberate information-bearing signal targeting Earth that emanates from much further away – perhaps even from the inner region of the Milky Way where there is a greater potential for other civilisations to have emerged.

In all of the SETI searches undertaken since 1960 using the world’s biggest radio telescopes, nothing has been detected except for one intriguing, never-repeated signal that was exactly where researchers expected a signal would have qualified if it had persisted. Known as the “Wow” signal because of the comment made by an observer of the computer sheet readouts of the 1970s, this strong narrow-band signal was detected from the constellation of Sagittarius in an area subsequently found to have planetary systems approximately in the line of sight. The frequency of the radio signal was very close to what is emitted naturally by neutral hydrogen, which is the most abundant element in the universe.

If another advanced civilisation was, like us, studying the universe through its neutral hydrogen, this is a highly logical part of the spectrum in which to detect a signal. There have been dozens of searches since the 1970s but the Wow signal has never been found again.

Without any doubt, uncovering either the “noise” or a deliberate radio transmission from an extraterrestrial civilisation is difficult and has a low chance of success. However, the chance of success is zero if we don’t even look.

With the SKA we will have the tools to search further and wider than ever before, thus reinvigorating hope that in the near future we may successfully detect the first signature of extraterrestrial life, either simple or complex.

Carol Oliver is the Deputy Director of the Australian Centre for Astrobiology at the University of New South Wales. Ian Morrison is the Square Kilometre Array Systems Engineer at Swinburne University of Technology.