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IS THERE LIFE IN THE SOLAR SYSTEM?

    When searching for extraterrestrial intelligent life, it seems obvious that the first place humanity would search would be its planetary neighbors in our solar system. However, even since the formation of SETI, few astronomers have been interested in searching Earth's companions around the Sun for extraterrestrial intelligence. The logic behind overlooking other solar planets is that in order to harbor intelligent life, the planetary body will have to first support simple life, which means the planet must have some semblance of water. Problematically, of all the bodies in our solar system, the only places known to have any form of water are Mars, and a few of the large moons orbiting jovian planets.

We can eliminate Mars as a candidate for one simple reason: we've seen it, all of it, in its entirety, and there is no intelligent life on it. Through the successes of the Mars Rovers and the Mars Global Surveyor, we now have detailed photographs of every region on Mars, and not a single one shows any evidence of intelligent life, let alone life at all. 

The other candidates, as large moons of Jovian planets pose more interesting questions. The nearest of these potential homes to intelligent life are three of the Galilean moons of Jupiter: Ganymede, Callisto, and even more fascinating than the others, Europa. All three are theorized to have massive subsurface oceans with conditions very similar to the oceans on Earth. As life on Earth began in such oceans, why could it not do the same on these moons of Jupiter? The fact of the matter is, these bodies may very well harbor life, but chances are that this life is primitive because in order to evolve into intelligent beings, the creatures would need enormous amounts of energy. In the Earth's case, the energy came trough the photosynthesis of our Sun's light, but these moons are not so fortunate. Because the ocean's are subsurface, very little if any sunlight would reach the living organisms. Consequently, these Galilean moons could not possibly harbor intelligent life, exhausting any remaining bodies of the solar system as potential homes to extraterrestrial intelligence. 
    

                           GALILEAN MOONS

    

As astronomer Jeffrey Bennett so poetically put in Beyond UFOs,

"There's no place like home, at least here in out own solar system. There's no other world in our solar system on which we could survive even a few minutes outside without a spacesuit, and no other world that has so much as a puddle of liquid water on its surface. This latter fact almost certainly means that we'll find no other intelligent life in out solar system because surface water seems a clear requirement for the evolution of complex beings like ourselves."

 Put bluntly, our solar system is not a prospect in the Search for Extra Terrestrial Intelligence.

 

LIFE AROUND OTHER STARS

With the amount of stars in our galaxy alone, and the amount of galaxies in the Universe, it is a pretty good assumption that there are conditions that could harbor life on another planets or moons somewhere other than here on Earth. There are more than 200 stars that we know of that have orbiting planets. Though, we have yet to find another extrasolar terrestrial planet. The Kepler Mission, which is scheduled for launch in 2008, is going to try to detect extrasolar terrestrial planets through the transit method (also known as the wink method, measuring the dimming of a star as a planet passes by in its orbit) of detection. Scientists hope to find 100’s of terrestrial planets through this mission.

Once other terrestrial planets are found, it is simply a question of whether or not the conditions present on that planet are suitable for life. That planet must be orbiting a star that is old enough to allow life to develop. This would rule out all stars of very high mass, which live only a few million years. This would eliminate roughly 1% of all stars, because low mass stars make up the majority of all stars. The star must allow for stable orbits of its planets. Half of all stars are in either binary or multiple star systems and stable orbits are not likely, although some systems like these do have planetary systems. Every star has a “habitable zone”, that is the region in which a terrestrial planet of the right size would have the correct surface temperature that would allow for liquid water and the development of life. The smaller the star, the smaller the habitable zone, which lessens the chance of such a planet falling within this region. (This problem can be seen in our own solar system, Venus is the right size, but is too close to the sun to fall into the habitable zone) Orbital properties measured by the Kepler Mission will tell us whether or not the terrestrial planets that it finds fall in the habitable zone of the star that they orbit.

Some scientists are proposing of the “rare Earth” hypothesis. This hypothesis states that the conditions that support life on earth are an example of luck. They believe that there is a small portion of the galaxy that has conditions that would create terrestrial planets that could harbor life. In the outer reaches of the Milky Way, there is a very low abundance of heavy elements and is mostly made up of hydrogen and helium. Terrestrial planets are made up of the heavier elements and it would not be likely that terrestrial planets would form in the outskirts of the galaxy. The inner galaxy is very crowded and supernovae are more probable in the inner region of the galaxy. Another part of the "rare Earth" hypothesis is the impact rate of objects in other solar systems. The impact rate has almost halted in our solar system and has allowed for life to develop here on Earth. Most of the comets, asteroids, etc. are located at the outskirts of our solar system and pose no threat to us. This is because they have been expelled out to their current orbital paths due to the presence of the Jovian Planets, especially Jupiter. 

There are many arguments that oppose the "rare Earth" hypothesis.  Some argue that the fact that Earth (made of heavy elements) is such a small fraction of the size of our sun (made of hydrogen and helium) could allow terrestrial planets to still form at the outskirts of galaxies where there is a low abundance of the heavier elements. Also it is unsure that the radiation of supernovae would really hinder the development of life. Such radiation could be shielded by a planet’s atmosphere or even could help life by increasing the rate of mutations and thus accelerating the rate of evolution. Without our moon, the large fluctuations of our axis tilt would happen over such a large interval of time that life could possibly adapt and could still continue on even with the extreme seasons. Also it may not be too rare to have such impacts of large planetary bodies during planet formation (like the impact of the Mars-sized object with Earth that created our moon). This would make it very likely that other extrasolar terrestrial planets could have large moons, like ours.

THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE

The search for extraterrestrial intelligence is the search for signals from other civilizations and is also called SETI.  In order for SETI to become a success there would have to be other civilizations broadcasting signals that we could receive.  We do not know if any other life exists beyond earth, so therefore we cannot know whether civilizations exist.  The drake equation allows us to determine the number of civilizations in our galaxy whom we might be able to communicate with.  

If there are other civilizations out there we should be able to communicate with them.  It is likely that we could encode signals in radio waves or in forms of light.  Majority of the SETI researchers are using large telescopes to search for alien radio signals.  Some scientists have begun to use visible light telescopes to search for communications encoded as laser pulses.  There is a chance that the civilization could be so advanced that the SETI will not detect them.  We have been sending high-power transmissions into space for about 50 years; anyone within 50 light-years of Earth could watch our old television shows.  In order for other civilizations to detect our broadcasts they would need more sensitive and bigger radio telescopes than we have today.  If anyone is sending signals nearby, we have a good chance of detecting them.

THE DRAKE EQUATION

In 1961, Astronomer Frank Drake wrote an equation to aid exobioligists in quantifying their estimates of the possibility of intelligent life outside of our solar system.  While many of the variables in the equation are still unknown, the formula allows scientists and others to use educated guesses in predicting a number of alien civilizations that we could communicate with today.  A modified version of his equation is given as where represents the total number of habitable planets, represents the probability that life will form on a planet, represents the probability that life evolves into an intelligent civilization that is able to communicate with us, and represents the probability that such a civilization is still around today (Bennet 514).

The only variable in the equation that science today can accurately predict is the number of habitable planets.  While no one knows the exact amount, it is reasonable to assume that there are at least a billion planets in our galaxy that lie in a habitual zone about their star to have liquid water.  Even if all the other variables are exceedingly small, say if only one in twenty of these planets yielded life, one in fifty of life bearing planets evolved to intelligent life, and only one in a hundred planets yielding intelligent life had civilizations that still exist today, the conservative estimate of alien civilizations we could potentially detect today would still be 10,000; and that is just a number for our galaxy.  The vast amounts of habitable planets that astronomers have predicted means that even if the occurrence of intelligent life forms is extremely rare, there is still a great possibility of life outside of our solar system, and it is this idea of making contact with an intelligent alien civilization that inspires the SETI Program.

INTERSTELLAR TRAVEL

In reality we have already begun to send space craft outside of our solar system.  These include the Pioneer 10 and 11, the Voyager 1 and 2, and the New Horizons craft.  These are unmanned vehicles that have the purpose of “falling” through space in the hope that someone will find them.There are many obstacles that we must overcome to be interstellar travelers.  For instance, if you put aside the technological shortcomings, the energy shortcomings, and the cost, the social aspect of the crew aboard the shuttle.  The length of time is would take to make the 50 light year round trip to the nearest star would pass by in only 2 years for the crew aboard the craft.  When they returned they would only be 2 years older but everyone else would have aged 50 years. Starships have been theorized and planned for a while now.  A few of the best ideas are some of the oldest.  In the 1960’s scientists proposed a design where a spaceship has a large “pusher plate” on the back where hydrogen bombs are exploded to push the ship into super speed.

Much of the reason interstellar travel is so desirable is the fact that we may be able to discover new civilizations and species.  The only problem with this is that by crunching the numbers we should have already seen multiple civilizations within our galaxy.  If we assume that our circumstances are similar, then there should be multiple worlds that are 70,000 to 1 million years ahead of us technologically.  If they were this advanced then they probably would have either found us or destroyed themselves in the process.

    Interstellar travel is currently impossible, and will most likely take a long time before it is plausible.  At the moment there seems to be the consensus that there are no other civilized areas in our galaxy.