THE LIGHTS IN THE SKY ARE STARS

SPECULATION: IS THERE LIFE ON OTHER WORLDS - PLANETS AROUND OTHER STARS OR PLANETS AND MOONS WITHIN OUR OWN SOLAR SYSTEM? THIS IS SOMETHING THAT PEOPLE HAVE WONDERED ABOUT FOR HUNDREDS OF YEARS.

“Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us.” - Calvin & Hobbes - “There are two possibilities. Maybe we’re alone. Maybe we’re not. Both are equally frightening.” - Isaac Asimov-

ANYTHING WE ENCOUNTER IN SPACE WILL PROBABLY NOT BE AS WEIRD AS SOME OF THE THINGS WE HAVE ON EARTH.

Before we can talk about life on other worlds, we probably need to define what we mean by life. I don’t think you can assume that life anywhere in the galaxy is just like life on Earth - that it has the same kind of DNA. Some scientists have come up with a list of the characteristics of life: 1.Life metabolizes 2.Life has complexity and organization 3.Life reproduces 4.Life develops 5.Life evolves

Or, we can use Carl Sagan’s definition that he came up with when he was working for NASA, and NASA largely uses: “Life is a chemical system that is capable of Darwinian evolution.”

If we encounter life on other worlds, most of it will probably be bacteria. It takes a very long time (if Earth is an example) for complex life to develop. Bacteria probably formed between 4 billion years ago and 3.5 billion years ago. More complex life did not develop until about 2 billion years ago, and multi-cellular organisms did not develop until about 600 million years ago. This is after 6/7 of Earth’s history to date had passed.

For life as we know it to exist, liquid water is necessary. This implies that the planet needs to be the right distance from the star. This is referred to as the “goldilocks zone.” Some scientists think that in addition to a goldilocks zone in a planetary system, there might be a goldilocks zone in a galaxy. Too close to the galactic center, and the chance for a supernova in the neighborhood increases the chance of major gamma ray bombardment. Too far out, and not enough supernovae occur to supply the elements needed for life.

To have carbon based life forms, similar to those that exist on earth, certain chemical elements are needed - carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, and a number of trace elements. Many of these are present in reasonable quantities in nebulas throughout our galaxy, having been formed in earlier star systems. Some scientists have speculated on the possibility of life forms being based on chemistry other than carbon. Whether this is possible, we just don’t know.

We do know that many of these elements exist in the great clouds of dust and gas that exist in galaxies, the nebulae. We also know that carbon compounds exist in some of these clouds. Meteorites that have fallen to Earth have been found to contain a variety of carbon compounds, including amino acids. The Murchison Meteorite that fell on Australia in 1969 contained 50 amino acids, 8 of which are essential to life.

Frank Drake proposed an equation in 1961 that expressed the probability of civilizations in the galaxy capable of communicating with other civilizations. N = N * f p n e f l f i f c L N * is the number of stars in the galaxy. Estimates range from 100 to 300 billion. However, if we limit this to stars similar to our sun, only 5% of the stars would be in that class or 5 to 15 billion.

f p is the fraction of stars with planets. Based the current searches for extrasolar planets, this is probably as high as 1.0. n e is the environmental factor. Is the planet in the “goldilocks” zone and does it have the right chemistry. Some scientists believe this could be as high as 0.1 or 10%. f l is the fraction of planets that might have life. Scientists involved in these studies put this between 0.1 and 0.2. f i if the fraction of planets on which intelligent life evolved. Best guesses are between 0.1 and 0.5.

f c is the fraction of planets with the ability to communicate with others using radio communication. L is the longevity of the civilization. Drake included this because he felt that intelligent civilizations may eventually destroy themselves. Consider the short time between the development of radio by Marconi and the use of the atomic bomb on Hiroshima. Drake believed that the number of civilizations that could communicate could be as high as 10,332 in our galaxy. Carl Sagan put the number at 1 million.

When one considers the distances involved, it will take time and technology. The nearest star is 4.2 light years from Earth, and the galaxy is 100,000 light years across.

This is the web site for the SETI Project - Search for Extraterrestrial Intelligence. This web site is for SETI at home - a computer sharing program to help in the data calculation. SETI also operates the Allen Telescope Array.

Videos on the Allen Telescope Array