Stars can’t help but beg the question: Are we alone in the universe?

Man has tried to answer this question numerous ways. The ancients assumed the heavens to be a realm of the gods. Since then, the gods have disappeared, replaced by Klingons, Xenomorphs and Tralfalmadorians.

But however imaginative or superstitious man might be about what lies beyond our immediate perception, the only answer science can offer so far is, “We don’t know.”

At least not yet.

The search for extraterrestrial life has yielded disappointingly few results, but we haven’t been at it for very long. In 1954, Frank Drake, a Cornell astronomer, developed the Drake equation, a way of quantifying the likelihood of life forming elsewhere using a simple formula which included, among other things, the number of planet-harboring stars, number of planets which form life and expected lifetime of a technological civilization.

Drake’s pioneering work led to the foundation of the Search for Extraterrestrial Intelligence (SETI). Using a radio telescope (a telescope attuned particularly to radio wave emissions) Drake attempted to see if anybody else was doing what humans were — broadcasting our presence to the rest of the cosmos through radio transmission.

Of course, Drake’s equation contains many built-in assumptions, one of which is that intelligent civilizations will broadcast. Humans have been broadcasting for about 90 years; long enough for our signal to reach the star Gamma Crucis 90 light-years away.

For comparison, our galaxy, the Milky Way, is about 100,000 light-years across. This means a millionth of our galaxy could possibly be aware of our presence, and they’d have to be fortunate enough to have the technology to “listen” during those 90 years.

In order for communication to actually happen, other civilizations must be listening at the same time we’re sending. For a star 90 light years away, a single back-and-forth communication would take 180 years.

If we assume the age of a technological civilization to be 500 years, the chances of a particular planet’s inhabitants hearing our broadcast would then be roughly .00002 percent at best, based on the not-unreasonable assumption that our galaxy has been able to produce life-supporting planets for 5 billion years. While it may appear bleak, this probability multiplied by the number of stars in the Milky Way is 2 million — if every star in the Milky Way is listening, given enough time, that many of them should hear us (and, ideally, we them).

Although it’s seriously unlikely every single star contains intelligent life-supporting planets, there’s a good chance life itself may be very abundant. When we look for the fundamental “stuff” of life — including water, carbon and even complex molecules like amino acids – we find it everywhere: in the atmospheres of other worlds, embedded in asteroids and even in interstellar space.

Of course, Earth is the only sample we have, the only world known to harbor life, but the life here dates to nearly 4 billion years ago, as far back as the geologic record will let us look. This suggests as soon as conditions on Earth allowed it to, life formed and spread.

Our own immediate galactic neighborhood, the Solar System, contains several potential candidates for life. Chief among these are Mars, which shows evidence of having at one time lakes and rivers on its surface and an early atmosphere similar to Earth’s, and Jupiter’s moon Europa, believed to contain a vast liquid water ocean beneath its cracked, icy surface.

And when scientists search for life elsewhere in the galaxy, it is water they look for first. Using a variety of sophisticated methods, including determining a “wobble” in a star’s orbit caused by orbiting planets and a dimming of the star’s light as a planet passes between the star and observers on Earth, astronomers are finding new planets in other star systems almost daily.

By characterizing the light emitted from a star, astronomers can determine the elemental composition of that star. A new mission, Kepler, is designed to look for Earth-like planets in nearby star systems. Where we see water and better still, free oxygen — which, as far as science currently knows, is only maintained by biological processes like photosynthesis — we will have a likely candidate for a life-supporting system.

Still, Earthlings have no reason to presume water and carbon to be fundamental to life. It may be harder to do, but other elements can do many of the same functions. Silicon, for example, can bond organic material together.

The resiliency of life on Earth suggests it could exist in just about any form. Recently-discovered “extremophiles” can live in volcanic vents and solid ice.

One recent study at the University of Manchester demonstrated spontaneous creation of RNA molecules. Simply get the right stuff together (and the “right stuff” is everywhere) and the basis for RNA molecules will combine. It’s simple chemistry, and the building block of life as we know it.

Civilizations like us may well have existed, but only for brief periods. One variable of Drake’s equation is the lifetime of a technological civilization. Creatures which evolve the technological capacity to destroy themselves must also evolve the (truly basic) morality required to avoid that fate.

If humans hope to have any chance of interacting with our cosmic neighbors, our morality must catch up with our technology soon. Otherwise, we may not be around to hear the “Hello” from Gamma Centauri.

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