CHANCES OF LIFE BEYOND THE SOLAR SYSTEM - PART 4
DEVELOPMENT OF LIFE
Now that we have established the fact that life can exist beyond our solar system but it is just really hard to find, let's take a look at what is needed for this life to thrive. Scientists believe that a wide variety of factors are needed in order for life to exist on other planets.
First, a planet must be at the right distance from its star, where the star can heat the planet so that it is not too hot and not too cold. This is necessary so that water can exist in liquid form. This favorable zone is called the habitable zone. Within the habitable zone, a planet may be able to support life. In our solar system, this zone would begin just outside of the orbit of Venus and stretching to the orbit of Mars. This means that a planet at Mars's location could potentially support life. Although, there are still even more factors that contribute to how a planet is heated, which means that a planet with life could be outside of the habitable zone depending on the solar system's characteristics. Since Mars has such a small mass, it is only capable of having a thin atmosphere, which prevents it from having water in its liquid form. But there might still be liquid water and life below the surface.
Second, a planet must have the time to develop life, particularly complex life. The more massive a star is, the faster it burns its compliment of hydrogen fuel. Our sun is five billion years old and if we get lucky, it will live another three or four billion years. High-mass stars can burn out in only ten to one hundred million years. While life may still have chance to form, there most likely will not be enough time for sophisticated life to form. Considering it took four billion years for intelligent life to develop on Earth, it is not known if this is a definite number.
While stars that are large and hot are not good for the development of life, stars that are too dim and cool are not good either. Most planets in these systems would be too far away to receive significant heat, even if they were within their habitable zones, they would face massive tidal forces. Since gravitational attraction increases as distance decreases, a planet within a short distance from its star, would be experiencing massive gravitational forces. Being this close to the star, the attraction on the near side would be much stronger than that of the far side of the planet, relative to the star. If there is a large difference in this attraction, it will literally rip the planet apart and create a ring or asteroid, but if it is less severe, the planet will actually reach a braking point and stop rotating. The star continues to pull and pull on the near side until that side is always facing the sun and the planets rotation about its axis actually equals that of its year. That is a long time to be under the sun. This is just like our moon as the same side faces us all year long by the gravitational forces acting between the Earth and the moon. A planet that has succumbed to these gravitational forces would be exceptionally unfriendly to life as one side would always be hot and the other cold.
Also, if the planet's orbit about its star is too eccentric or elliptical than it will face dramatic temperature changes throughout the year it is moves closer and further from the sun.
A change in the planet's tilt on its axis will also cause climatic changes. The tilt in the axis of the planet will allow the temperature to change throughout the year, allowing each area on the surface to experience different climates. A tilt of more than 54 degrees would cause the climate to change too much and the poles would become hotter than the equator. Such a difference in climate would not be able to allow life to survive long enough to evolve. It is it believed that our moon stabilizes our axial tilt of an average of about 23 degrees. Every 41,000 years, our tilt oscillates back and forth from about 22 to 24.6 degrees. It is also believed that without the moon, our tilt would oscillate back and forth from 0 to 85 degrees. A tilt of this magnitude would not have been able to allow life to evolve.
Another factor that is detrimental to the creation of life is meteoroid impacts. Meteoroids are chunks of matter floating through space. They vary from tiny specks of dust to huge chunks miles in diameter. Scientists believe that Jupiter and Saturn act as shields against large meteoroid impact. They believe that their large gravitational forces have been able to attract the biggest meteoroids towards them, stopping them on their way to Earth. Even though small impacts cannot harm us, scientists believe that an object 6 miles across led to the destruction of the dinosaurs. It is believed that without Jupiter and Saturn, the Earth would undergo such an impact every ten thousand years. It's hard to believe that life could live through such an onslaught.
So how many planets out there have these characteristics? It is probably hard to believe for anyone that all these factors are needed in order for life to thrive. This is probably becuase of the fact that we have been subjected to the many views of science-fiction. The Star Trek episodes tell us that on every planet there is a different life form. Is this possible? Not likely. Even Star Wars is filled with life in every solar system, like the moon of Endor, Tatooine or Naboo. Based on the facts that I have given you, is it likely that there is as much life out there as we would like to think? I am not saying that there is no life out there at all, but is it as abundant as we like to believe. We will just have to wait and see what technological advances will be used to answer these questions.
Cavelos, Jeanne The Science of Star Wars 1999. Publisher: St. Martin's Griffin.