Searching for aliens

Jill Tarter is a strong advocate of the scientific search for extraterrestrials.

Of all the sci-fi films and programmes to have hit the screens since 1902, when George Melies' celebrated Le Voyage de le Moon showed chicken-headed selenites greeting the intrepid Earthling explorers, Contact stands apart.

There've been plenty of low-budget sci-fi films that have saved on costumes and makeup by aliens assuming human form, or films featuring benign aliens - think of the loveable ET.

There have been even those in which Earth is, for once, not under attack by an advanced alien civilisation - in 2001: A Space Odyssey it is superior aliens who help primitive humans to develop technological skills.

What makes Contact special, even nine years after its release, is simply that it is more real.

To begin with, it is based on a book written by a real scientist, inspiring cosmologist Carl Sagan; the locations are real - the 305m radio telescope at Arecibo Observatory in Puerto Rico and the Very Large Array in New Mexico; and its heroine, Ellie Arroway, played by Jodie Foster, was modelled on lively radio astronomer, Jill Tarter.

Tarter, who was selected by Time magazine as one of the world's 100 most influential and powerful people in the "Scientist and Thinker" category, is in New Zealand for the Dunedin International Science Festival.

She has been for decades a world leader and strong advocate for the scientific search for evidence of life on other worlds, and is Director of the Search for Extra Terrestrial Intelligence Institute (Seti).

Was her screen alter ego, Ellie Arroway, an accurate portrayal and why, when it comes to aliens, is the science so much more compelling than the fiction?

"Fundamentally I think the character was Carl himself, but there were a lot of situations the character faced which I experienced trying to break into science - and my dad did die when I was 12. That turns out to be not uncommon for women my age who ended up in science and engineering.

"For most of us, our fathers were the central figures and the motivators of our lives, and when we lost them we got a rude lesson in missed opportunities.

"But we were left with just enough stubbornness and extra determination that we wanted to do something that would make our fathers proud, and that allowed us to somehow turn a deaf ear to all this cultural programming we were getting about not needing calculus or physics because we were just going to have babies and all that nonsense." (Tarter is also widely respected for her promotion of scientific literacy particularly among girls and women.)

That "stubbornness" led Tarter to a PhD in astrophysics from the University of California and while finishing it in the early 1970s, she read the "Cyclops Report", an engineering design study on how to detect extraterrestrial intelligence which suggested building a large radio telescope array.

"I was really impacted by it," says Tarter, "because I realised that I happen to live in the first generation of human beings capable of trying to answer this question we've asked ever since we first walked out of caves, looked at the sky and wondered 'Are we alone?'

"Until now all we've been able to do is ask the priests and philosophers, and the only answers we got back were based on belief systems.

"But here we suddenly had the tools to at least begin trying to answer the question observationally - to go look for the data instead of asking people what they believed. That was pretty impressive to me."

Impressive, but not easy. A decade earlier, Frank Drake had come up with his famous equation of the factors which would determine the number of intelligent, communicating civilisations in the Milky Way.

At the time, almost the only factor astronomers had a good approximation for was the number of stars in the galaxy - about a hundred billion. It took another 35 years to develop the technology to begin trying to answer the second factor - how many stars have planets? In the past 10 years, we've managed, painstakingly, to discover planets orbiting about 150 stars in the galaxy. There's still a very long way to go.

Isn't she daunted? "No - I couldn't think of anything more exciting or impressive to work on. It isn't as immediately rewarding as studying phenomena that you know are there, but if we don't look we'll never know."

While the galaxy may be teeming with extra-solar planets, conditions for intelligent life are far harder to satisfy.

Planets must be the right distance from a star, within the "goldilocks" zone, where it is not too hot and not too cold for liquid water; the star must be stable and old enough to have given intelligent life time to evolve (it took 4.6 billion years on Earth); the nebula from which it formed had to contain the heavy elements like carbon, nitrogen and oxygen on which life depends; and, most importantly, there must have been sufficient time for technology to develop - it took humans about a million years to develop communication technology.

Finding and targeting suitable stars is difficult enough, but with the small amount of observing time the privately funded Seti Institute has on radio telescopes around the world, constant surveillance and whole sky coverage are impossible. The institute is solving the problem in two innovative ways.

The first is seti@home which uses the combined computing power of millions of PCs to sift through the huge amount of recorded data available from a number of radio astronomy projects, identifying any unusual signals. Tarter describes how the world's largest distributed network began. "A guy from Microsoft had the idea. We had a piggy-back programme operating at Berkeley, so we gave them our real-time algorithms to look for signals." It was an immediate success. "Seti@home was such a sexy application for distributed computing that it turned the world onto this idea. Now there are all kinds of things you can do at home - fold proteins for cancer research, count craters, find minor planets. It's a great way for people to support research."

The second is the Allen Telescope Array (ATA), a revolutionary radio interferometer comprising 350 linked antennas. Currently under construction, the ATA is named after the co-founder of Microsoft, Paul Allen, who contributed US$13.5 million ($22.4 million) for the first two construction phases.

"It's an enormously fast survey telescope with high spatial and spectral resolution - we'll be looking at lots of stars much more quickly than we've been able to," says Tarter. "And for the first time we are going to be able to actively remove satellite interference. The price is an enormous amount of computer power - but we can do it. "

And if a signal is found? "From the beginning we've had the philosophy that we are going to detect signals," she says. "Our biggest challenge is discriminating among the signals and trying to decide which signals are our own technology and which might be coming from someone else's technology. We automatically do a number of tests that try to figure out what its origin is."

But will they come from an advanced civilisation?

"Well we're young - our technology is only 100 years old, our galaxy is only 10 billion years old and there are older stars than the sun.

"But if there are signals there to detect, it means that technology has lasted a long time. Of course it's possible that by the time we detect something, the civilisation that sent it might not exist - it takes a long time to cross the galaxy.

"But," she smiles, "it's pretty unlikely that they would be around and just happen to go off air around about the time we show up."

How they scan the stars

Detecting a signal is one thing, finding the planet it came from is another. The search for extra-terrestrial intelligence is paralleled by the search for extra-solar planets.

Every one of the approximately 150 extra-solar planets detected since 1995 using the technique of gravitational microlensing has involved New Zealand astronomers in the MOA (Microlensing Observations in Astrophysics) project.

A predominantly Japanese/New Zealand collaboration, MOA is based at Mt John Observatory at Lake Tekapo, and uses the new 1.8m telescope "Moatel", funded by Nagoya University. It's the largest telescope in New Zealand and is the world's largest telescope dedicated to microlensing.

Professor Phil Yock, of Auckland University, a leading astronomer from the MOA team, explains how it works.

"Microlensing occurs when light from a distant star or galaxy is bent by the gravity of an intervening star passing directly in front. This distortion causes the star to brighten temporarily and small 'defects' in the brightening indicate planets around the star."

Husband and wife team Michael Albrow and Karen Pollard, from Canterbury University, belong to another successful microlensing team, Planet. Both teams contributed to the recent discovery of a Neptune-sized planet and expect that microlensing will be the most efficient technique for detecting Earth-like planets in the future.

That will suit Grant Christie and Jennie McCormick, from Auckland Stardome, who last year became the first amateur astronomers to have contributed to the discovery of a planet since William Herschel discovered Uranus in 1781.

In spite of their amateur status, Christie and McCormick are highly experienced astronomers and respected members of the international microlensing network MicroFUN.

Dr Denis Sullivan, of Victoria University, and his son Tiri have been one of the few teams to have detected an extra solar planet recording the tiny drop in luminosity of the star HD209458 as a planet crossed in front of it.

"Detecting planetary transits is very rare", says Sullivan, "because the plane of the planet's motion about the star has to be almost precisely aligned with the observer."

And should the joint Australia/New Zealand bid for the Square Kilometre Array, the world's biggest radio telescope, be successful, it's likely that New Zealand astronomers will be involved in detecting large numbers of extra-solar planets.

And the answer is ...

N = N* fp np fl fi fc L

This is one form of the equation that Professor Frank Drake of the University of California came up with in 1961 to help scientists examine the factors involved in the development of intelligent civilizations.

There is no unique solution to the equation as the number changes according to the values put in, but it is a useful tool to focus research and discussion.

Human existence proves there is at least one planet around one star where intelligent (though this has been subject to debate) life evolved to develop communication technology. But the sun around which Earth orbits is only one of 100 billion stars in the galaxy so the rest is guesswork!

The number of intelligent communicating civilisations in the galaxy (N) is dependent on N * (the number of stars in the galaxy), fp (the fraction of stars with planets), np (the number of suitable planets per star that are capable of sustaining life), fl (the fraction of planets where life starts), fi (the fraction of planets where intelligent life evolves), fc (the fraction of intelligent species that develop communication), and L (the length of time that communication has been in use is a fraction of the planet's life during which the communicating civilizations live).

* Jill Tarter is speaking at Auckland University of Technology, Wellesley St, 4pm Friday, July 7.