LOJ Feb 2004

E.T.

The Search for ExtraTerrestrial Life

LOJ Feb 2004

Syllabus Extract: How can we search for ET?

• We may be able to observe living organisms (e.g. microorganisms), or their fosilised remains, directly, for example, by actually going to Mars or Europa (a satellite of Jupiter), by using robots to send back pictures or by using robots to collect samples to bring back to Earth;

LOJ Feb 2004

Syllabus Extract: How can we search for ET?

• We may be able to detect living organisms by the chemical changes they produce in a closed system (e.g. inside a closed container or in the atmosphere of their planet).

• Because of living organisms, the atmosphere of the Earth is very different from what it would be purely from chemical and geological processes; for example, there is much more oxygen;

LOJ Feb 2004

Syllabus Extract: How can we search for ET?

• We may be able to receive signals from other species with technologies that are at least as advanced as our own.

• The search for extra-terrestrial intelligence (SETI), using radio telescopes to try to find meaningful signals in a narrow band of wavelengths has gone on for more than forty years, so far without success.

LOJ Feb 2004

Syllabus Extract: How can we search for ET?

• Candidates should be able, when provided with appropriate information, to evaluate:– the methods scientists use to discover

whether there is life elsewhere in the Universe;

– evidence that such life exists.

LOJ Feb 2004

SETI

• SETI is an acronym for

Search for ExtraTerrestrial Intelligence.

LOJ Feb 2004

What is SETI?

• It is an effort to detect evidence of technological civilizations that may exist elsewhere in the universe, particularly in our galaxy.

• There are potentially billions of locations outside our solar system that may host life.

• With our current technology, we have the ability to discover evidence of cosmic habitation where life has evolved and developed to a technological level at least as advanced as our own.

LOJ Feb 2004

What is Project Phoenix?

• Project Phoenix, run by the SETI Institute, is the most ambitious search for extraterrestrial intelligence ever undertaken.

• Since 1995, it has been scrutinizing the vicinities of nearby, Sun-like stars, hoping to pick up a signal that would tell us that we're not alone.

• Project Phoenix is a direct descendent of the NASA Targeted Search that was ended by congressional action in 1993.

LOJ Feb 2004

How is Phoenix different from other experiments?

• It is the only targeted search. • In other words, rather than sweeping large

swaths across the sky, Phoenix zeroes in on nearby stars. By restricting its attention to carefully selected targets, the 28 million channel Phoenix receiver can accumulate radio energy for minutes (rather than seconds), providing unequaled sensitivity to weak signals.

LOJ Feb 2004

How is Phoenix different from other experiments?

• Project Phoenix also checks out all signal candidates within 20 minutes of their discovery, using a second radio telescope in Jodrell Bank, England. This is important, because the hot gas between the stars can cause signals from distant star systems to fade up and down over a few hours' time.

LOJ Feb 2004

How do we know if the signal is from ET?

• Virtually all radio SETI experiments have looked for what are called "narrow-band signals."

• These are radio emissions that are at one spot on the radio dial. Imagine tuning your car radio late at night… There's static everywhere on the band, but suddenly you hear a squeal - a signal at a particular frequency - and you know you've found a station.

LOJ Feb 2004

How do we know if the signal is from ET?

• Narrow-band signals, say those that are only a few Hertz or less wide, are the mark of a purposely built transmitter. Natural cosmic noisemakers, such as pulsars, quasars, and the turbulent, thin interstellar gas of our own Milky Way, do not make radio signals that are this narrow. The static from these objects is spread all across the dial.

LOJ Feb 2004

How do we know if the signal is from ET?

• In terrestrial radio practice, narrow-band signals are often called "carriers." They pack a lot of energy into a small amount of spectral space, and consequently are the easiest type of signal to find for any given power level. If E.T. is a decent (or at least competent) engineer, he'll use narrow-band signals as beacons to get our attention.

LOJ Feb 2004

What happens if we find something?

• The receivers used for SETI are designed to find constant or slowly pulsed carrier signals… something like a flute tone against the noise of a waterfall.

• But any rapid variation in the signal - known as modulation, or more colloquially as the "message" - would be smeared out and lost.

• In order to understand anything that E.T. might be saying to us, we'll have to build far larger instruments to look for the modulation of his signal. It's more than likely that, once a detection is made, the money will become available to build this far larger instrument.

LOJ Feb 2004

What happens if we find something?

• Until we can measure the modulation, all we'll know is that there is intelligence out there.

• We can pinpoint the spot on the sky where the signal is coming from, and slow changes in its frequency will tell us something about the rotation and orbital motion of E.T.'s home planet.

• Even with this limited information, the detection of alien intelligence will be an enormously big story.

• We'll know we're not alone, and we're not the smartest things in the universe. And of course there will be a loud clamor to build the big dishes that would allow eavesdropping on E.T.'s message.

LOJ Feb 2004

Then what?

• Suppose we get the message?

• Will we understand it?

• No one knows, of course.

• It's conceivable that an advanced and altruistic civilization will send us simple pictures and other information.

LOJ Feb 2004

Why do we think that life is "out there"?

• Over the last half-century, scientists have developed a theory of cosmic evolution that predicts that life is a natural phenomenon likely to develop on planets with suitable environmental conditions.

• Scientific evidence shows that life arose on Earth relatively quickly, suggesting that life will occur on similar planets orbiting sun-like stars.

• With the recent discoveries of extrasolar planetary systems, and the suggestive evidence that life may once have existed on Mars, this scenario appears even more likely.

• Additionally, one should keep in mind that we are only one planet around a very ordinary star. There are roughly 400 billion other stars in our Galaxy, and nearly 100 billion other galaxies. It would be extraordinary if we were the only thinking beings in all these enormous realms.

LOJ Feb 2004

What is the Drake Equation?

• The Drake Equation was originally developed as an agenda for a 1961 scientific meeting.

• It provides a way of estimating the number of intelligent civilizations existing in our galaxy that might be broadcasting signals.

• Among the factors considered are the number of sun-like stars in our galaxy, the fraction of habitable planets supporting communicating civilizations, etc.

• When these various factors are multiplied together one can compute N, the number of transmitting civilizations. Unfortunately, many of the factors are poorly known, so estimates of N range from one (we are alone in the Galaxy) to thousands or even millions.

• Try it out yourself http://www.classbrain.com/artmovies/publish/article_50.shtml

LOJ Feb 2004

Why do SETI at all?

• There are many reasons, including such practical considerations as the technological spinoff. The signal processing techniques used for Project Phoenix have already been applied to the detection of breast cancer.

• But SETI research is first and foremost pursued because it is designed to answer questions that previous generations could only ask.

• How do we fit into the biological scheme of the cosmos?• Is intelligent life a rare event or a common one in the

universe? • Can technological civilizations last for long periods of

time, or do they inevitably self-destruct or die out for some other reason?

LOJ Feb 2004

Why do SETI at all?

• If we could understand any signal that we detect, there’s always the possibility that we could be presented with enormously valuable knowledge.

• It is likely that any civilization we discover will be far more advanced than ours, and might help us to join a galactic network of intelligent beings.

• But even if we detect a signal without being able to understand it, that would still tell us that we are not unique in the universe.

• The effect on society might be as profound and long lasting as when Copernicus displaced the Earth from the center of our universe.

LOJ Feb 2004

What can you be asked?

• To recall that life as we know it requires sunlight, carbon and water (at temperatures that allow it to be liquid).

• To recall what SETI stands for and how and why it uses radio signals.

• To be able to make sensible comments on data provided on the methods used to detect and evidence for life outside our Earth.