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Thoughts on the Square Kilometer Array

We now know that the vast collection of radio dishes and antennae that will become the Square Kilometer Array (SKA) will be built on two sites, with the majority of dishes in Phase 1 (beginning in 2016) being constructed in South Africa, and further dishes added in Australia as the project develops. The SKA is to be a radio telescope of unprecedented sensitivity capable of sky surveys at frequencies from 70 MHz to 10 GHz. A SKA news release notes that “All the dishes and the mid-frequency aperture arrays for Phase II of the SKA will be built in Southern Africa while the low-frequency aperture array antennas for Phase I and II will be built in Australia.”

Combining the signals from the project’s dishes, mid-frequency aperture arrays and low-frequency aperture arrays will offer a telescope with a collecting area equivalent to a dish with an area of one square kilometer, a truly formidable observing platform. Phase 1 construction will involve about 10 percent of the array and will involve dishes and low-frequency aperture arrays. Phase II is to begin several years after Phase I is complete, but funding for this part of the project has not been guaranteed.

Image: The proposed Square Kilometre Array (SKA) radio telescope. Credit: AAP.

Astronomy Now’s Keith Cooper looks at the recent announcement in South Africa and Australia Share SKA Spoils, noting that both the MeerKAT (Karoo Radio Telescope, in South Africa) and ASKAP (Australian SKA Pathfinder) precursor telescopes have already been built, prompting the advisory committee to choose inclusivity as the best option. The idea is to maximize existing investments in both countries, but I’m still surprised by the result. From Cooper’s article:

What makes their decision slightly controversial is that the organisation’s own Site Advisory Committee had ruled that while both bids were excellent, South Africa had the edge overall after considering criteria such as levels of radio interference and long term sustainability of a radio quiet zone, the physical characteristics of the site, long distance data network connectivity, operating and infrastructure costs as well as the political and working environment.

And from an article in South Africa’s Times Live:

The eagerly awaited decision now means that engineers can connect antennas at Australia’s core site at Mileura station, about 100 kilometres (60 miles) west of Meekathara in western Australia. Other antennae are distributed across Australia and New Zealand.

South Africa’s site in the arid Karoo region will now also be connected by a remote link to a network of dishes stretching across southern and eastern Africa and as far away as Ghana.

What the SKA Can Do

The SKA is one of the primary global science projects of the early 21st Century, with a charter to study the earliest eras of the universe, between the epoch of recombination, when charged electrons and protons first became bound (from which came the Cosmic Microwave Background we can study today) and the emergence of the first galaxies. But its proposed areas of investigation range widely, from the large-scale structure of the universe as affected by dark energy to the workings of pulsars and black holes. For our purposes on Centauri Dreams, it’s useful to focus on the role the SKA has to play in exoplanet studies, while its potential in the area of SETI is impossible to ignore.

Combining signals from widely separated antennae allows us to achieve high resolution at radio wavelengths, making the SKA a potent tool for investigating the habitable zones of Sun-like stars in their infancy. The developing array will be able to image the thermal emission from dust in the habitable zone and chart the flow of the small particles that eventually go into making planets. Imaging features in protoplanetary disks will help us track the formation of giant planets as they open up gaps in the dust, and should offer a look at both the core accretion model of planet formation — the slow growth of dust grains into rocks and planetesimals — and the gravitational instability model, in which planets grow out of disruptions in the surrounding disk.

As for what other kinds of signals the SKA might detect, the project’s planners seem most enthusiastic about SETI. The SKA website claims that its vast network will be sensitive enough to detect an airport radar on a planet 50 light years away. Indeed, a fully fleshed out SKA should be sufficiently sensitive to detect signals comparable to our own television transmitters operating on planets around the stars closest to the Sun. While traditional SETI has proceeded largely through a search for directed beacons, the SKA will allow a search for leakage radiation from nearby stars, while expanding the range of our search for beacons by a factor of 1000.

Given our own brief window of visibility at television wavelengths as we increasingly go to cable and satellite technologies, the prospect of detecting an alien television signal from the handful of stars near enough to make it possible is inconceivably remote. On the other hand, this is the first time we can make a good case that a civilization not much more advanced than our own could indeed pick out signs of intelligent life from all those old Milton Berle broadcasts we’ve sent.

Meanwhile, it’s fascinating to consider other surprises that the SKA might produce. One possibility is the detection of so-called ‘rogue planets’ that wander the interstellar deep without a star. Last year we looked at the work of Heikki Vanhamaki (Finnish Meteorological Institute), whose calculations showed that a gas giant rogue planet with a large moon could produce auroral effects detectable out to a range of 185 light years by an array as formidable as the Square Kilometer Array. Given the number of rogue planets that may be out there (Vanhamaki thinks there could be as many as 2800 within that 185 light year range), detection of at least a few may be a possibility (see Finding an Interstellar Wanderer for more on this work).


Comments on this entry are closed.

  • Michael Roberts May 30, 2012, 10:34

    I can’t quite contain my excitement to the possibilities of the SKA. Very excited.

  • David H May 30, 2012, 10:48

    Paul, you haven’t mentioned another SKA precursor telescope that is also under construction currently, the Murchison Widefield Array (http://www.mwatelescope.org/). This is a survey instrument that will see very large areas of the sky continuously, permitting the detection of unexpected, transient and other events. The MWA is the precursor to the low-frequency SKA and will be built entirely in Western Australia. Work on the MWA has been underway since 2005 and is very, very promising. SKA-low is expected to look back in time to the age before the formation of the first stars, the epoch of reionisation (EOR).

  • Greg May 30, 2012, 11:32

    “The SKA website claims that its vast network will be sensitive enough to detect an airport radar on a planet 50 light years away.”

    Amazing sensitivity! The one issue is, there’s approximately 49,000 airports with radar’s on earth, the signal from one would be washed out, leading to the my main query, how do separate out the noise from the signal from that distance and determine what that signal is?
    I remember a few years ago that a radio telescope for low frequency signals was being constructed unfortunately I forgot the name of the program. If we could at least detect a signal in the 10 – ~100 hertz range we could determine if there is a civilization that uses AC type electrical current.

  • ljk May 30, 2012, 15:50

    Project Cyclops lives!


    This page includes a link to the entire Cyclops document in PDF format:


  • Mike May 30, 2012, 20:43

    The wonderful things that can be done if the money can be found. I would really like to see the discoveries that the SKA would surely produce. The more we look the more we find.

    To Greg, you mention a ELF radio telescope working at 10 to 100 Hertz?
    Because of the ionosphere that would have to be space-based or maybe the Moon’s farside. Pretty pricey but I wonder what it would find. No one has ever done any Extremely Low Frequency radio astronomy. If you can recall the particulars about the project you mentioned please post it.

  • David May 31, 2012, 1:57


    Actually there were two such satellites, Explorer 38 and Explorer 49.
    See http://en.wikipedia.org/wiki/Explorer_49

    Radiation from the Earth dominated the radiation from other sources at these low frequencies so the second satellite was put into Lunar orbit in order to use the Moon to block it out.

  • Bob Andrews May 31, 2012, 9:32

    The mid-sentence phrase ‘not much more advanced than our own’ flags up both the expectations of SETI and it’s limitations. Any highly advanced civilisation would be using technologies such as ‘faster-than-light’ communication and/or propulsion systems and therefore undectable by our present science.

    SKA will (if fully funded and implemented) play an important role in future space exploration. Excitement is indeed in the air!!

  • Mike May 31, 2012, 12:25

    To David, I’ve just looked at your link to Explorer 49 and according to Wikipedia it examined the radio spectrum from 25KHZ to 13.1MHZ. That is indeed below what LOFAR can usually see but it’s certainly not ELF.
    Nobody has done ELF ( 3 to 300 Hertz) radio astronomy and it may not be possible within the Heliosphere as studies suggest such long wavelengths may not pass through the boundary between solar space and the interstellar medium but who knows?
    The very low end of the radio spectrum is unexplored for radio astronomy so who knows what surprises might await there. The thing is, who wants to fund a space-based radio telescope with, for example, 50 mile long antennas?

  • Gerry May 31, 2012, 17:54

    This question is sort of related to Bob Andrews’ point, above. If the array will be sensitive enough to conceivably detect a radar-type signal, would it be able to detect and characterize the emissions from artificial energy sources such as atomic-powered spacecraft under thrust, or atomic detonations in space (perhaps as a component of asteroid mining, or a Daedalus/ICAN II type engine, for instance)? Seems like energized plasma harnessed for interplanetary travel would put out a broad signal of some intensity.

    Obviously, this is pretty unlikely, but considering what we know to be physically possible in our own future, maybe it’s not such a far fetched notion. Even if interstellar travel is rare, interplanetary travel might not be.
    Let’s just hope they don’t limit themselves to solar sails!

  • Kris June 2, 2012, 17:24

    Given there is a sphere of electromagnetic radiation, roughly 90 Light years radius, moving at the speed of light in every direction from Earth, some 100,000 star systems have now been exposed to our leaked radio messages, if they can detect them.

    Perhaps we should be listening to stars that would have heard our message and could send us a stronger return signal.

    Paul or others, do you know if there has been any systematic SETI project to listen carefully to each of the stars within say, a 45-LY radius, having had enough time to compose and respond with a beacon signal?

  • Paul Gilster June 2, 2012, 22:34

    Kris, Project Phoenix, which began in 1995 and was privately funded, did some of this. Here’s a clip about it and then a URL:

    Unlike many previous searches, Phoenix didn’t scan the whole sky. Rather, it scrutinized the vicinities of nearby, sun-like stars. Such stars are most likely to host long-lived planets capable of supporting life. We naturally include stars that are known to have planets. Project Phoenix observed about 800 stars. All are within 200 light-years distance.

    More here:


  • Eniac June 4, 2012, 20:39

    The very low end of the radio spectrum is unexplored for radio astronomy so who knows what surprises might await there. The thing is, who wants to fund a space-based radio telescope with, for example, 50 mile long antennas?

    Interesting concept. It need not be expensive at all. 50 miles of wire can be unspooled with not too many problems, and would probably make for a good ELF antenna, kept in place by slow rotation or gravity gradient. A bunch of these in solar orbit would make a nice ELF ultralong baseline interferometer, capable of high resolution imaging.

  • Marcin June 6, 2012, 17:12

    “Last year we looked at the work of Heikki Vanhamaki (Finnish Meteorological Institute), whose calculations showed that a gas giant rogue planet with a large moon could produce auroral effects detectable out to a range of 185 light years by an array as formidable as the Square Kilometer Array. Given the number of rogue planets that may be out there (Vanhamaki thinks there could be as many as 2800 within that 185 light year range)”

    Well… taking into account latest research on ‘nomad’ planets (http://arxiv.org/abs/1201.2687) there is about 10^5 of them per main sequence star.

    Considering Milky Way’s star density (0.000424 per ly^3) then in the sphere of radius 92,5ly there should be about 140 MILLION ‘nomad’ planets :) I don’t know about the probability of gas giant ‘nomad’ planet formation but that would have to be 1 per 50k to get us to 140 million number (considering 2800 of them in 92,5 ly radius).

  • Marcin June 6, 2012, 19:49

    For some reason I assumed 185ly is a diameter… but it actually is 185ly radius in the article. My last paragraph should then the look like this:

    Considering Milky Way’s star density (0.000424 per ly^3) then in a sphere of radius 185ly there should be about 1,1 BILLION ‘nomad’ planets :) I don’t know about the probability of a gas giant ‘nomad’ planet formation but that would have to be 1 per 400 000 to get us to 1,1*10^9 figure (considering 2800 of them in 185ly radius).

  • ljk June 27, 2012, 22:36


    SETI on the SKA

    by Keith Cooper for Astrobiology Magazine

    Moffett Field CA (SPX) June 27, 2012

    SKA’s low frequency antennas in Australia.

    It was a vision of the search for extraterrestrial intelligence that was never meant to be. In 1971 NASA’s Ames Research Center, under the direction of two of SETI’s great heavyweights – Hewlett-Packard’s Barney Oliver and NASA’s Chief of Life Sciences, John Billingham – sponsored a three-month workshop aimed at coordinating SETI on a large scale.

    While laying the groundwork of much of what was to follow for SETI in the subsequent decades, such as the existence of the ‘water hole’ between 1420 and 1666MHz, it also investigated what SETI could do if money and resources were no option.

    By the end of the three months they had come up with Project Cyclops, which detailed plans for an immense array of radio dishes, up to a thousand in all, each dish 100-meters across with a total collecting area of up to 20 square kilometers.

    Cyclops would have been able to hear the faintest whisper, the quietest murmurings from ET, capable of picking up rogue leakage from their civilizations or being deafened by the blaring signal of a deliberate beacon.

    Cyclops was never built of course; it was never intended to have been. Rather it was a thought experiment, a look at what was possible if SETI scientists had carte blanche to build whatever they wanted.

    Indeed, 100-meter dishes are just about the largest we can build before they become structurally unstable. They’re also expensive, but crafty radio scientists have realized that linking many smaller and cheaper radio dishes together in a process known as interferometry can create a combined collecting area equal to or larger than those single dishes, and far more efficiently.

    As such, today we stand on the cusp of a new era in radio astronomy, one that could give SETI the boost it needs to discover that we are not alone. In May 2012 it was announced that the Square Kilometer Array (SKA) – an ambitious network of thousands of radio antennas – would be based in both South Africa (in addition to neighboring countries) and Australia.

    Assuming funding is in place, construction on phase one is set to begin in 2016, phase two in 2019, with the whole venture to be complete by 2024. South Africa will get the majority of radio dishes, each one 15 meters across, designed for targeted observations, while Australia will have the low frequency antennas and mid-frequency phased array dishes for wider-field survey work.

    It’s not quite on the scale of Project Cyclops but, overall, the size of the SKA is still enormous, with initial baselines (the widest distance between telescopes in the interferometer; the longer the baseline, the greater the angular resolution) of hundreds of kilometers, with phase two expanding that to 3,000 kilometers. A veritable forest of radio antenna on two different continents, listening to the stars.

    Whereas Cyclops was designed to be a SETI-dedicated array upon which other astronomical projects could piggyback, the SKA is the mirror image, an instrument primarily for seeking neutral hydrogen in the early Universe, for examining emission from pulsars and black holes and exploring cosmic magnetism.

    Yet the search for life and its origins has never been far from the SKA’s priorities, with plans to probe the interiors of planet-forming dust discs around young stars to search for the building blocks of life in those planetary construction yards.

    There’s also SETI and the possibility that the SKA could chance upon an artificial radio signal from another world. So would SETI experiments be welcome on the SKA, perhaps piggybacking at no extra cost on other astronomy experiments as SETI does on Arecibo?

    That’s an affirmative, confirms Dr Michiel van Haarlam, the SKA’s Interim Director General. “It’s not been put to the test yet but it is definitely being considered,” he says. “It’s on our list of science cases so I think it will be there, in competition with all the other proposals out there.”

    So, what could SETI do on the SKA? Suffice to say, alien searches have rarely been attempted on very long baselines. More often than not SETI has been performed on single dishes and when interferometry has been utilized, such as on the Allen Telescope Array (ATA), it’s rather localized with short baselines, but very long baseline interferometry (VLBI) is finding itself increasingly in vogue. How does SETI perform on telescopes of such size?

    The bane of SETI is terrestrial interference from the likes of television and radio, cellphones, orbiting satellites and airport radar. With a long baseline array of so many telescopes across such a wide stretch of land, is it feasible to eradicate all interference? It turns out you don’t need to, says Hayden Rampadarath of the International Center for Radio Astronomy in Perth, Australia.

    He led a SETI VLBI experiment to listen to the Gliese 581 system – a red dwarf with at least four orbiting terrestrial planets – using the three telescopes of the Australian Long Baseline Array.

    The report on the experiment, to be published in The Astronomical Journal, describes how, despite no extraterrestrial signals bring received, the system did detect and successfully identify 222 narrow and broadband signals of terrestrial origin.

    “Because of the large separations of the individual telescopes, hundreds to thousands of kilometers, the same radio frequency interference would usually only be seen by one or two telescopes and, as such, would not be correlated,” says Rampadarath.

    “However, sometimes this might not be true and interference that does correlate would instead experience a geometrical delay – and hence a phase delay – that arises due to the radio emission arriving earlier at some of the telescopes than at others.”

    This phase delay could then be used to rule out any rogue emission – the point being that long baseline interferometry on the SKA need not worry about interference from terrestrial signals, therefore making the array an excellent tool for targeted SETI operations.

    Whereas our interference is an obstacle for SETI, extraterrestrial radio interference may provide an opportunity. The SKA’s promotional literature has frequently talked about being able to eavesdrop on ET’s own terrestrial radio signals, neatly sidestepping the issue of whether ET would spend the resources on deliberately beaming a signal to us.

    Certainly our own rogue radio signals have been permeating space for almost a century, but they’re weak, dropping off with distance following the inverse square law; the SETI Institute’s Seth Shostak has previously pointed out that we couldn’t even detect our radio signals with our current equipment at the nearest star, Proxima Centauri, 4.2 light years away. What hope then do we have of detecting ET’s version of tacky reality television and soap operas?

    It depends on whom we ask. “For phase one of the SKA, we can detect an airport radar at 50 to 60 light years,” says van Haarlam.

    Professor Abraham Loeb, Chair of the Astronomy Department at Harvard University, goes even further. In 2006 he wrote a paper with his Harvard colleague Matias Zaldarriaga that was published in the Journal of Cosmology and Astroparticle Physics, describing how upcoming radio observatories such as the SKA could eavesdrop on radio broadcasts.

    “Military radars in the form of ballistic missile early warning systems during the Cold War were the brightest,” he tells Astrobiology Magazine. “We showed that these are detectable with an SKA-type telescope out to a distance of hundreds of light years, although TV and radio broadcasting is much fainter and can be seen to shorter distances.”

    It is undisputed that our over the horizon radar has powerfully leaked out into space. However, those early warning radars are in most cases, like the Berlin Wall, a relic of a past time, used for only a few decades before becoming obsolete.

    Today they have been mostly replaced by broadband radars that hop across frequencies, making them untraceable to extraterrestrials, a theme that’s been latched onto in a paper published in The International Journal of Astrobiology by Dr. Duncan Forgan of the University of Edinburgh and Professor Bob Nichol of the Institute of Cosmology and Gravitation at the University of Portsmouth.

    They worry that, if extraterrestrial civilizations followed our technology curve, with the move over to digital broadband signals, they would have reduced their radio leakage and made their planets ‘radio quiet’, leaving a window of only about a century where we can eavesdrop on them.

    “If we are able to improve our technology so that our signal does not leak out into the Galaxy and if we improve it on a certain timescale, then our estimates suggest that even if our Galaxy is well populated but with human-like intelligence that decides to drastically curb its signal leakage, then it becomes very difficult to detect them,” says Forgan. If that’s the case, then the chance of the SKA’s existence coinciding with one of those relatively short time windows of extraterrestrial leakage is going to be small.

    It gets worse. Although Forgan accepts that radar will still be directed into space to probe potentially hazardous near-Earth asteroids, this use of radar is random and non-repeating, points out Dr. James Benford of Microwave Sciences, Inc. who, along with John Billingham, assessed our own civilization’s visibility in a paper presented at the Royal Society’s ‘Towards a Scientific and Social Agenda on Extraterrestrial Life’ discussion meeting in October 2010.

    They calculated that a transmission deliberately beamed into space by the 70-meter Evpatoria radio antenna in the Crimea, far more powerful than our TV and radio leakage, would only be detectable as a coherent message by a SKA-sized receiver out to 19 light years, and as a raw burst of energy containing no information out to 648 light years.

    Worse still, they argue that Loeb’s calculations for our TV and radio leakage being detectable out to 75 light years – calculations that are based on very long integration times on the order of months – are not feasible because radio stations will rotate over the limb of a planet, preventing locking onto the signal for a prolonged period of time to facilitate detection (Benford levels the same criticism at van Haarlam’s estimate of detecting airport radar out to 50 light years).

    Furthermore, in response to Seth Shostak’s claim that a receiver the size of Chicago could detect our radio leakage out to hundreds of light years, Benford and Billingham respond by pointing out that such an antenna, with a total collecting area of 24,800 square kilometers, would cost $60 trillion, of similar order of magnitude to the planet’s entire GNP (for comparison, the SKA is projected to cost around $1.5 billion).

    If ET is going to hear us, they’re going to have resources far in advance of our own, meaning that our own efforts to eavesdrop with the SKA are going to be futile.

    The picture painted by Forgan and Nichol, Benford and Billingham is pretty bleak for eavesdropping with the SKA. However, Loeb counters, “The periodicity due to rotation of a planet is a big plus that can help in identifying the artificial nature of the signal.” He adds, “In addition to planetary rotation, one could search for periodicity due to the orbit of the planet around its star.”

    Benford isn’t convinced by Loeb’s arguments. “Absence of signal [as the planet rotates] means absence of detection time and the signal-to-noise ratio is reduced,” he says.

    However, we’ve been assuming that our aliens are planet-bound. Suppose they have spaceflight. That could change things quite a bit. Radio communication between satellites, space stations and spacecraft would not be subject to planetary rotation. Duncan Forgan admits that he hasn’t factored spaceflight or interplanetary colonization into his vision of a radio quiet Universe, but cautions, “It’s unclear exactly how much radio traffic would result from a civilization that has multiple planets around multiple stars.”

    There are other methods of communicating, he says, such as lasers or even ephemeral neutrino beams. On the other hand, notes Jim Benford, a planet-faring civilization may use microwave beaming to power their spacecraft, dramatically increasing their leakage signature.

    Ultimately, whichever side of the debate you fall on, there are a lot of unknowns and assumptions built into each argument that renders neither of them entirely persuasive. Maybe the SKA won’t be able to eavesdrop on ET, but there’s certainly no harm in trying. If it fails, there is always more traditional SETI to fall back on, namely the search for deliberate beacons.

    Benford imagines the existence of transient beacons, designed to be cost efficient, flashing our way only once in a given timeframe. These, he says, look a lot like pulsars, something that the SKA is primed to search for; perhaps a transient beacon will manifest itself in one of the SKA’s pulsar sweeps? It’s the potential for this kind of serendipitous discovery that could make the SKA such a powerful tool for SETI, as long as the manpower and resources are there to search through all the raw data that the SKA will produce.

    Certainly, there will be lots of it: in order to process all the data covering millions of one hertz wide narrowband channels, exaflop computers that are capable of performing on the order of a million trillion operations per second will be required. There’s only one problem: such powerful computers have not been invented yet, but Moore’s Law and recent advances in computing tell us that they are on their way and will be ready by the time the SKA is online.

    Jim Benford suggests making things even simpler. Searching for transient beacons is going to require a lot of watching and waiting, staring unblinkingly in the hope of catching the brief burst of a transient signal in the act – something like the mysterious ‘Wow!’ signal, perhaps. According to Benford, a small array of radio dishes, each tasked with observing a particular patch of sky non-stop, would do the trick.

    There’s no need to use the entirety of the SKA, he says; the small array of dishes that form ASKAP, Australia’s SKA Prototype, would be sufficient and far more efficient at a fraction of the cost of using the entire SKA.

  • ljk March 28, 2013, 9:35

    Review: A Single Sky

    The field of radio astronomy emerged after World War II as scientists turned technologies developed during the war towards the skies. Jeff Foust reviews a book how this field developed far more collaboratively than many other scientific endeavors.

    Monday, March 25, 2013