Who's Out There?
from the book, "Our Fascinating Earth"
Who's Out There?
It is common knowledge that astronomers measure distances in outer space by light—years, the distance light will travel in one year at the rate of over 186,000 miles per second. Reducing this to terms that make sense to the nonastronomer, one must translate a light—year into a common unit of measurement, such as miles.
As an illustration, allow the distance from the moon to the earth, approximately 240,000 miles, to be represented by the thickness of an ordinary playing card. If one were to continue adding cards to the stack, each card representing the distance from the earth to the moon, it would take about nineteen miles of playing cards, at six million cards per mile, to reach the distance from earth to the nearest star, Alpha Centauri, 4.3 light—years away.
The earth is part of the Milky Way galaxy, at some distance south—west of the center. If the stacking of playing cards were to continue until the equivalent distance from earth to the center of the galaxy were reached, a continuous stack could be assembled that would go five times around the equator of the earth (something like 120,000 miles of cards).
The number of stars contained in the entire universe is impossible to fathom. Our galaxy alone, which is only medium—sized, contains more than one hundred billion stars. Multiply this by the ten billion or so other galaxies within observable limits, some containing many times that number, and the only possible star count is "beyond our comprehension." Space, obviously, is not empty, but on closer observation it seems not to be incredibly cluttered. Light from the Large Magellanic Cloud, one of our nearest neighbors in the cluster of about thirty galaxies called the Local Group, takes 170,000 years, a little less than one light—year, to reach the earth.
The universe itself, or space, is so vast that, traveling at the speed of light, it would take at least 30 billion years to cross from one of its borders to the opposite — and 100,000 years just to cross our galaxy. And still the universe continues to expand! Most scientists believe that, among the conservatively estimated 100,000 million, million, million (10 to the 23rd power — with 23 zeros — or 100 sextillion) stars in the universe, there must be other planetary systems that contain the necessary criteria to sustain some forms of life.
No criteria prescribed that a star must be the size of our sun, or of any particular size, mass, brightness, or energy range, to have a planetary system. The size of stars varies greatly; some are gigantic by any standard of comparison and certainly dwarf our medium—sized sun with a diameter of 865,400 miles. Its size, mass, brightness, and energy range are such that it supports life on the third planet, Earth, that averages 93 million miles distant.
Recently scientist discovered a faint blue star that is believed to be the largest yet identified. It is at least ten times hotter than our sun, with a diameter about the size of our solar system. The star, named R—136a, is 150,000 light—years from earth (or a stack of more than 3.6 trillion playing cards). It is in the Large Magellanic Cloud, one of the Milky Way's galactic clusters. Scientists believe that in just one second this star puts out more energy than our sun does in five years!
It is intriguing to imagine the forms of life that could be supported by a star of such size, which radiates such heat and energy. The planet orbiting this sun with a seven—billion—mile diameter would have to be far enough away to avoid being pulled into it and to receive a minuscule portion of its light, heat, and energy. Since Pluto, at the edge of our solar system, makes a 247 year revolution around the sun, any life—giving planet around R—136a would have a revolution, or year, calculated in light—years. Truly the life forms on R—136a would stretch the imagination of the most creative writers of science fiction.
Various attempts have been made to communicate with possible extraterrestrial life forms. On August 20, 1977, Voyager 2 spacecraft set sail for distant planets and beyond, on a mission to contact other worlds. Aboard Voyager is a copper phonograph record containing a 120—minute recorded message from Earth. Included in the recording are greetings in several languages and a variety of sounds from nature, blips that can be decoded into 116 photographs, and 90 minutes of music ranging from Bach and Stravinsky to Chuck Berry's "Johnny B. Goode."
Would extraterrestrials of a planet such as R—136a think of Voyager as the work of a primitive civilization? Would our recorded sounds of nature and music seem like skittish, jittery insects? The likelihood that our message will be received by beings of another world is rather remote, considering that it will be 40,000 years before Voyager 2 passes by the nearest star. Our descendants can only wait and hope that our message in a bottle will eventually encounter life in another part of the universe.