by Duncan Lunan

On 23^rd February 2022, the Astronomers of the Future Club in Troon’s guest speaker was Professor Michael A Garrett, inaugural Sir Bernard Lovell chair of Astrophysics at the University of Manchester and Director of the Jodrell Bank of Centre for Astrophysics – a group of 190 people, including postgraduate students, based at the Alan Turing Building on the University campus in Manchester and Jodrell Bank Observatory, home to the iconic Lovell Telescope.  JBCA runs e-MERLIN, the UK’s radio astronomy National Facility, on behalf of the Science & Technology Facilities Council.

Michael has a particular interest in the Search for Extraterrestrial Intelligence, and is currently vice-chair of the SETI Permanent Committee of the International Academy of Astronautics in Brussels.  So he was able to give us an up-to-the-minute briefing on the current state of SETI, rather that the usual historical review.

Just 10 days earlier, in my article on ‘The Milky Way’, I had said that our Galaxy contains at least 200 billion stars, possibly as many as 400 billion, depending on the numbers of red dwarf stars, which are hard to detect outside our immediate neighbourhood.  Early in his lecture, Michael Garrett casually updated that to at least 500 billion, based on the latest data from the Gaia satellite and other surveys.  With the number of known planets of other stars now exceeding 5000, again from space telescope surveys, it’s likely that all of them have planets or have had them in the past.  And as I pointed out in ‘Life on Other Worlds’, on January 9^th, from the ongoing exploration of our own Solar System we now know that it’s possible that all of its planets and several of its moons could harbour ‘life as we know it’ in some form, to say nothing of more exotic possibilities.

It’s hard to understate what a turnaround this is since I wrote my first book Man and the Stars in the early 1970s.  The 1930s idea that ours might be the only planetary system in the Galaxy was taking a long time to die, and although since the 1950s other models of stellar and planetary formation had gained ground, it was still thought that planets might be rare.  The classic formulation of probabilities, the ‘Drake Equation’ formulated by Prof. Frank Drake, the originator of the first search for interstellar signals, supposed that the number of communicative civilisations might be a product of the rate of star formation, the fraction of stars resembling the Sun, the fraction of those with planets, the fraction of planets resembling Earth, the fraction of those developing life, the fraction of those developing intelligence, the fraction of those developing technology, and finally how long such civilisations might last.  The rate of star formation was believed to be one star per year, and depending on the values you chose for the other fractions, the number of communicative civilisations could be anywhere between one and several thousand.  On the most optimistic estimates, the average distance between civilisations might be a thousand light-years, and the original acronym was changed from CETI  (Communication with Extraterrestrial Civilisation)  to SETI  (‘Search for…’), on the assumption that all we could detect the beacons of other civilisations which had chosen to announce their presence at the time, even if they were probably now long dead.

As I said in ‘The Milky Way’, the whole picture now looks quite different.  So far from being constant, star formation in the Milky Way has a history of billions of years of near-stasis, punctuated by intense bursts of star formation triggered by collisions with smaller galaxies.  The earliest stars in the Galaxy would have been composed of hydrogen and helium, formed in the Big Bang, and heavier elements would have been formed and spread by supernovae explosions of giant stars, but collisions between neutron stars would have formed more and spread them much faster, so life could have appeared in the Galaxy much earlier than had been thought, around 10 billion years ago.  I mentioned  (in ‘Stars and Nebulae’, January 30^th)  that stars had been found in the Galactic Nucleus which were 13.5 billion years old, apparently predating the formation of the Milky Way itself, and only 300 million years after the Big Bang.  I might have mentioned that some of the globular clusters, composed of very old ‘Population II’ stars and orbiting in the galactic halo, were apparently 12 billion years old or more, apparently predating the nucleus.  But even since Prof. Garrett’s lecture, it has emerged from Gaia data that the thick disc of the Milky Way spiral is all as old as 13 billion years, formed and generating heavier elements 2 billion years before the Gaia-Enceladus collision triggered the formation of the Thin Disc and the Population 1 stars we know today.  (Rahul Rao, ‘Parts of the Milky Way Are Much Older than Thought, Study Reveals’, Space.com, 22^nd February, 2022.)

Michael Garrett didn’t spend long on the implications of those discoveries for SETI.  But given that the possibilities are so much wider than used to be thought, so too are the capabilities of the search.   We’re no longer looking just for the very powerful beacons of perhaps a very few civilisations, but for the ‘technosignatures’ of what could be many more out there.  We should now be able to detect the changes to their environment made by energy-intensive civilisations, including but not limited to narrow-band communications, and such activity could be revealed by the relative motions of its sources  (planets or space installations)  relative to the stars that they orbit.

Frank Darke’s initial Project Ozma in 1960 could target only two stars, for a few hours apiece, on one frequency, and could only have detected signals deliberately aimed at us.  Modern searches use much larger instruments, listening on many channels simultaneously, and the Breakthrough Listen project founded by Yuri Milner is using the Green Bank radiotelescope, the Parkes telescope in Australia  (featured in The Dish)  and the Very Large Array in New Mexico  (featured in Contact), along with the more recent Murchison array in Australia, which is part of the growing transnational Square Kilometre Array, along the MeerKAT array in South Africa.  The recent loss of the Arecibo facility  (featured in Goldeneye)  is a major blow, but it may be replaced by FAST, its huge Chinese counterpart. Their target is to study 100 million stars for technosignatures, while compiling an Exotica Catalogue of other astronomical phenomena worthy of future study. 

According to NASA’s Goddard Space Flight Center, the Exotica Catalog will include ‘one of everything’ in the universe.  Nor are they limiting themselves to radio waves:  the four optical 12-meter telescopes of the Very Energetic Radiation Imaging Telescope Array System (VERITAS), Fred Lawrence Whipple Observatory, Amado, Arizona, are conducting Breakthrough Listen’s search for interstellar laser signals.  At Jodrell Bank, the Galactic Plane Survey is evaluating not only the million Breakthrough Listen target stars, but everything out to and including 100 million light-years beyond and around them, within the lobes of the Breakthrough Listen radio search.  It will increase the number of possible sources being studied by 100 times.  In 2020 they were already able to announce that of 198,000 stars ‘closer than about 330 light years ‘in the Gaia catalogue, ‘fewer than one in 1,600’ has Earth-level transmitters.  There will bc an enormous increase in capability with the new facilities coming on line shortly, in radio  (improved ALMA and SKA), infrared  (James Webb Space Telescope)  and optical  (Euclid, Vera Zubin, the 30-metre telescope on Hawaii, the Extremely Large Telescope in Chile), to name only a few.

To date, the only possible SETI detection is classed Breakthrough Listen Candidate 1, a narrow-band signal heard coming from Proxima Centauri  (once only, so far).  Very interesting though that would be, for reasons which I’ll explain in a future article, its characteristics resemble a certain obscure type of computer equipment and it’s almost certainly a false alarm from somewhere near the receiver.  Long-baseline interferometry, which will become available to Breakthrough Listen when the SKA becomes operational, will make it easier to eliminate false alarms, because when one telescope array detects a nearby signal by chance, the other one will not.  It will give any future detection much higher credibility, as well as helping to pinpoint the source.  Passing spacecraft will also be much more easily detectable, and that too is a subject for a further article.

Looking for artificial signals in the output of distant galaxies might seem fantastic, but one has to consider what kind of a power law there might be, giving their ratio to natural signals.  In certain wavebands the Earth’s output is already far above what’s generated by natural sources.  The SKA will be able to detect ‘leakage’ similar to Earth’s at 100 light-years, which makes it a sobering thought that the Beatles’ appearance on the Ed Sullivan Show is still on its way out there, having passed Alderamin  (Alpha Cephei)  in 2013.  Prof. Nikolai Kardashev postulated that there are three SETI-related levels of high-technology civilisation:  Level 1 controls the matter and energy of a planet, Level 2 of a Solar System, and Level 3 of a galaxy.  Prof. Garrett suggested that a Kardashev 2 or 3 civilisation would use so much energy that it would disturb the infrared-to-radio power law for star formation in galaxies.  I’m not so sure:  the closing chapter of my book Man and the Planets argued that ‘control’ implies restraint, or at least the possibility of it, as opposed to Freeman Dyson’s nightmarish vision of intelligence as ‘a purposeless technological cancer’, bringing destruction to one planetary system after another.  I argued that to achieve true Kardashev 2 status a civilisation would have to become conservationist, and if Kardashev 2s collectively evolved to Kardashev 3s they would be galactic gardeners, not industrialists.  That may make them a great deal harder to detect – indeed, since we don’t see the wreckage of their failures, the proof of their success may be that we can’t see them out there.

Towards the end of Prof. Garrett’s lecture, one aside made me sit up sharply.  At the energy levels he was contemplating, he said, there might be anomalies between the spectroscopic properties of a star system and its geometric layout.  I had worked on just that with the late A.T. Lawton, subsequently President of the British Interplanetary Society and UK representative on the SETI Committee of the International Astronautical Federation.  We were looking at a case where the dynamical parallax of a binary star system  (which allows one to estimate the masses and spectral types of the two stars, if their approximate distance is known), appeared to show that the minor sun was about 2000 degrees too hot for its mass.  Lawton had published a paper on generating a maser effect in the atmosphere of the Sun to turn it into a SETI beacon, and maybe we could create a laser powerful enough to heat up the minor sun we were looking at, by similar means.  Lawton went off to Herstmonceux, then the Royal Observatory, with a first draft of our joint paper, to discuss the idea with Geoffrey Burbidge, who had suggested that a giant laser could trigger a supernova by similar means.  He came back with a flea in his ear and forbade me to publish or discuss “that fanfaronade” in any form thereafter, and although he and I went separate ways a year or so later, I’ve never done so until now.  I no longer have my notes on the matter, but I shall certainly create something from memory for Prof. Garrett to look at.

Check out: The Sky Above You – April 2022