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Give thanks for life on planet Earth

November 1, 2007 12:36 am

AS WE GIVE thanks this month, I am reminded of a question my 9-year-old son recently asked me. He wanted to know why the Earth could sustain life while other planets in our solar system are lifeless places.

Although he did not realize it, his question was a fundamental one that has continually intrigued astronomers. Is ours the only planet in the universe where intelligent life has been able to prosper?

Mercury, Venus, Earth and Mars are the four inner planets of the solar system. The inner planets are small, rocky worlds, while the outer planets of Jupiter, Saturn, Uranus and Neptune are large and gaseous.

Sometime during the formation of the solar system, our planet began to differentiate itself from its solar system brethren. Earth contained a hospitable atmosphere, with oxygen and copious amounts of liquid water on its surface.

In addition to possessing life-giving water, our planet's temperature is neither too hot nor too cold for life to exist. Our distance of 93 million miles from the sun happens to be in the solar system's region where life could flourish.

Astronomers take these and other factors into consideration as they study the possibility of life in the universe beyond our solar system.

In 1961, astronomer Frank Drake devised his famous equation, which attempts to mathematically estimate the numbers of intelligent civilizations in the Milky Way. Try it yourself at pbs.org/lifebeyondearth/listening/drake.html.

Even before Drake's equation, astronomers had speculated that stars outside our solar system probably had planets orbiting them. However, the technology did not exist to support the theory until 1995, when the first planet outside our solar system was discovered.

Since then, more than 250 planets, most of them gas giants like Jupiter, have been discovered orbiting distant stars in our Milky Way galaxy. Most recently, astronomers using NASA's Spitzer Space Telescope have discovered an Earth-like planet forming 424 light-years away from us.

In addition, a new space mission to be launched in early 2009 named Kepler (kepler.nasa.gov) will concentrate on finding Earth-like planets around distant stars.

As techniques and technology continue to slowly improve, our discoveries will become more intriguing. But will we ever have a definitive answer to the question of life beyond Earth?

It may not happen in our lifetime or even our children's lifetime, but if life were ever discovered outside the solar system, the impacts would be tremendous, and would transcend both science and religion.

Then again, if we never detect signs of life from distant solar systems, it would underscore the fragility and importance of our existence in the universe.

So while we're enjoying Thanksgiving feasts this month with family and friends, let's not forget to give thanks for our planet Earth. It's the one and only home shared by humankind in the universe.

November offers the opportunity to see the five planets that are visible without using any optical aid.

Jupiter is first to come into view, very low in the southwest after sunset. It will be near the crescent moon on Nov. 12. This is the last month to catch Jupiter in the evening before it disappears in the sun's glare.

About three hours after sunset, look for bright, ruddy-colored Mars rising in the east. Mars will continue to brighten this month in preparation for its best viewing in December. Look for it near the moon during the morning of Nov. 27.

Golden-colored Saturn is next to make an appearance in the eastern sky, well after midnight. Look for it near the moon during the mornings of Nov. 3 and 4. A small telescope will enable you to see Saturn's beautiful rings.

As the brightest object in the sky after the sun and moon, Venus continues to be dazzling this month in the morning sky. The brilliant planet will be near the moon on Nov. 5, making a lovely sight in the eastern sky as people travel to work.

The planet Mercury makes its best appearance of the year this month, before sunrise in the eastern sky. It will be a few degrees above the very thin crescent moon on Nov. 8 about 45 minutes before sunrise. Ensure you have a clear, unobstructed eastern horizon as the pair will be very low in the sky.

Not many people have seen Mercury, since it is always positioned so close to the sun, so make the most of this opportunity!