The view of Christiaan Huygens, the Dutch mathematician and physicist who discovered Saturn's moon Titan in 1655, was as follows: Now can anyone look upon, and compare these systems (of Jupiter and Saturn) together, without being amazed at the vast magnitude and noble attendants of these two planets, in respect of this little pitiful Earth of ours? Or can they force themselves to think, that the wise Creator has disposed of all his animals and plants here, has furnished and adorned this spot only, and has left all those worlds bare and destitute of inhabitants... or that all those prodigious bodies were made only to twinkle to, and be studied by some few perhaps of us poor fellows? (qty. in Sagan, Cosmos 130) Millions of dollars and many brilliant minds have long been dedicated to unlocking the great mysteries of the universe. Perhaps the greatest mystery is whether or not life exists on planets other than Earth. Plato, Epicurus, Isaac Newton, and Benjamin Franklin all shared a belief in extraterrestrial civilization ("Search" par.

10). Due to newfound understandings of the size and complexity of the universe, the current knowledge of life and its ability to thrive in even the most extreme circumstances, and lack of a reasonably unquestionable skeptical view, the answer to "Are We Alone?" is undoubtedly "no." The sheer size of the universe presents unlimited possibilities for extraterrestrial life. There are an estimated one hundred billion (100, 000, 000, 000) galaxies in the universe ("By the Numbers"). The Milky Way galaxy, which houses the solar system that is home to Earth, is some 100, 000 light years across (1 light year is equivalent to 5. 9 trillion miles). It contains approximately four hundred billion (400, 000, 000, 000) stars (Chyba par.

18). Among the factors used to determine how suitable a star is for supporting habitable planets are energy, gravity, and life spans of these stars as relative to time necessary for the evolutionary process to take place (Browns berger). There are seven main spectral classifications, including (listed from hottest and largest to coolest and smallest) types O, B, A, F, G, K, and M. Types O and B, which make up less than two percent of the four hundred billion stars in our galaxy, are the only classes believed to be incapable of supporting life (Zubrin 232).

Type G stars, the same type as our very own Sun, number around a couple hundred million inside the confines of the Milky Way (Morrison par. 5). In order for life to exist, not only must there be stars, but there must also be planets. In April of 1999, astronomers announced the first discovery of a solar system other than our own.

This solar system consists of three large planets that orbit the star Upsilon Andromeda e, forty-four light years away ("Astronomy" par. 1). In August of 2000, scientists discovered that the star Epsilon Eri dani, which lies a mere 10. 5 light years from Earth, harbors a planet. It could even harbor another solar system (Cowen par. 2).

Thanks to new Doppler techniques, the technology of direct orbit wobble viewing, and other methods used by astronomers, there is now evidence of some twenty extra-solar planets. This sample suggests that somewhere between ten and a hundred million solar systems could be found in the Milky Way galaxy around Sun-like stars (Morrison par. 8). As Carl Sagan so eloquently stated: Despite its 10, 000-million-mile diameter, the solar system is dwarfed by the Milky Way galaxy to which it belongs. But the Milky Way... is only a mote in the universe.

There are thousands of millions of such galaxies, most with their own myriad stars having their own planetary systems. If only 1/10, 000 of 1 percent of these planets harbor a civilization - and this is a very conservative estimate - the universe must teem with more than 100 million million civilizations." (Planets par. 21) It has already been proven, by scientific experiments involving "Mars Jars," that many earthly micro-organisms are capable of surviving under Martian conditions, including extreme cold, dryness, and variance in atmospheric pressure and composition (par. 9).

Here on Earth, life is known to flourish in the most extreme environments, including lava-spewing volcanoes, nuclear reactor cores, and layers of subzero arctic ice (Origins: Astrobiology par. 2). Life on Earth is well-adapted because this is where it has always been. Naturally, life forms originating on another planet would be well-adapted to that planet as well (Sagan, Cosmos 14).

Is it not reasonable to assume that life originating elsewhere in the universe would be no less adaptable to extreme heat, cold, and even radioactivity than life on Earth? Many believe liquid water and oxygen to be necessary factors in the existence of life. But if terrestrial organisms exist that are capable of thriving without free oxygen, why wouldn't extraterrestrial organisms be capable of this same feat? This, of course, is assuming that they don't require some other form of gas for respiration. The same can reasonably be said for liquid water. Perhaps alien life forms are capable of retaining a water supply in their tissues and acquiring alternate forms of water from the environment (Sagan, Planets par. 9). Thus far, scientists are only able to study and compare life on Earth.

This gives them a very limited knowledge when viewing life on a cosmic level (Sagan, Cosmos 4). Many scientists harbor a belief in subsurface life forms, which may inhabit places such as Mars and the moons of Jupiter. It is already known that there is a subsurface biosphere on Earth that possibly equals or even exceeds the mass of all organisms on Earth's surface. This certainly supports the possibility of subsurface life on Mars or Jupiter's moons (Chyba par.

5). The Galileo spacecraft has shown evidence for oceans beneath the ice surfaces of the Jupiter moons Europa, Callisto, and Ganymede. Since liquid water is necessary for life on Earth, proof of liquid water on these moons greatly increases the chance of extraterrestrial life in our solar system (Na eye). Terrestrial life is based on organic molecules, which are now known to be plentiful throughout space (Chyba par.

2). Radio emission lines shown by gas clouds prove this presence of carbon compounds (Morrison par. 9). And though the presence of these molecules and compounds certainly does not prove that life exists in outer space, it is definitely a foundation for it. Biophysicist Stuart Kauffman believes that life is an unavoidable result of chemistry ("Search" par. 31).

The chemistry is undoubtedly there. Though the argument for the possibility of alien life forms throughout the universe is quite strong, there are still many opponents. The most often used reasoning by these skeptics is known as the Fermi Paradox, which asks the seemingly simple question, "Where are they?" Physicist Enrico Fermi proposed that in the suspected 12-15 billion-year age of the universe, sentient alien life forms have had more than ample time to spread throughout the galaxy, colonizing habitable planets. This would naturally include Earth (Shostak).

There are many logical reasons for why they have not yet reached Earth. Some, including SETI (Search for ExtraTerrestrial Intelligence) pioneer Frank Drake believes interstellar travel to be so costly and impractical that the aliens never leave home. Others believe that those capable of interstellar travel follow a code of noninterference with backward or emerging civilizations (Chang par. 12). It could be that intelligent civilizations are common throughout the universe, but they never survive past a certain point as a direct result of nuclear war, greed, pollution, or some other threat to civilization (Sagan, Cosmos 247). Perhaps intergalactic travelers feel that we on Earth are not ready for the realization of extraterrestrial beings, and that we must first learn to live in harmony amongst ourselves.

Maybe the aliens just haven't reached this part of the galaxy yet (Chang par. 12). Maybe they have, but we are unable to detect their technology, or they are part of the wide range of incompletely understood phenomena in astronomy (Sagan, "Cosmic" par. 13).

And who is to say that they even care to visit us in the first place? Retired physicist Michael Hart provides another case for disbelief in extraterrestrial life. He believes that the origin of life is an astonishingly rare coincidence (Chang par. 10). In an ABC News online chat, he stated, "The main problem is not life existing or evolving, but life originating in the first place (Hart)." Stephen Hawking, Luc asian Professor of Mathematics at Cambridge University, and commonly thought of as one of the greatest minds of our time, provides an excellent counterpoint to Hart's assumption. Hawking theorizes that if the origin of life were unlikely, it would take a considerably long time for it to begin. Subsequently life would evolve to intelligent forms with little time left before being destroyed by the swelling of the Sun at the end of its ten billion year life span.

Fossil evidence proves that life on Earth began some 3. 5 billion years ago, a mere five hundred million years after the Earth's environment is believed to have become suitable for life to develop. Hawking goes on to say that instead of taking the possible seven billion years to originate, life developed in only about one-fourteenth of the time available. This suggests a good chance for "spontaneous generation of life, in suitable conditions (Hawking pars. 10-12)." Much of the doubt of extraterrestrial existence is directed towards SETI, an ongoing project devoted to detecting radio transmissions from outer space.

Skeptics point out that since its beginning over forty years ago, SETI has not produced any affirmation of extraterrestrial life (Hart). Since 1992, SETI has analyzed over five hundred trillion signals, but has not discovered even one alien signal ("Search" par. 33). Many, including Tulane physicist Frank Tiller, believe the SETI project to be a waste of both time and money (Gardner). What most SETI doubters fail to mention is that Project Phoenix, SETI's current project, will only examine several stars out of every billion in the Galaxy. They " ve only examined about one-billionth of the galaxy to date (Chyba 18-19).

Nobody said that the chances for extraterrestrial intelligence were that great! In conclusion, the physical constructs of the universe, combined with the determination of life to adapt and survive, make it very hard to deny the great likelihood of life on other planets. Even the most logical of skeptics provide theories that are easily questioned. Though there is not currently any concrete proof of the existence of extraterrestrial beings, it would be impossible to prove that they do not exist elsewhere in the vast expanses of the universe. It is therefore imperative that we continue our search.

As author and internationally renowned astronautical engineer Robert Zubrin wrote, "To be really alive as individuals, to be really alive as a civilization and as a species, we must be willing to continually seek out and experience the new... when we cease exploring, we die (283).".