Incredibly, two teams of U.S. astronomers estimated last week that the Milky Way galaxy probably contains at least 100 billion planets, and perhaps 17 billion of them are Earth-size. This mind-blowing news was announced at the winter assembly of the American Astronomical Society in California.
Actually, no astronomer has seen a planet outside Earth's own solar system. The lightless bodies can be detected only when their gravity causes a host star to wobble, or when they pass in front of a host star, causing it to dim temporarily. The new Kepler space telescope is designed for such detection, and it's finding thousands of examples.
For centuries, scientists had no evidence that distant planets existed. But in the past decade, a floodgate opened. So far, nobody knows how many mid-size planets are in the "Goldilocks zone" -- not too hot, not too cold, but just right for liquid water and possible life. Another crucial factor is star stability. Earth's sun is steady and stable, but some other stars pulse and flare destructively.
The breakthrough wave of planet discoveries raises the tantalizing hope that humans are not alone as the only thinking creatures in the universe. If the Milky Way contains 100 billion planets, similar numbers presumably exist in each of the billions of other galaxies flung to infinity. It's brain-boggling to contemplate such vastness.
Writing in The Philadelphia Inquirer last week, physicist Paul Halpern said Earth's special role as the only known home of life should make people stop killing each other and focus instead on preserving the planet "like a garden of rare orchids."
Already, he noted, warfare has diminished greatly -- and the European Union won last year's Nobel Peace Prize because Europe has ceased centuries of conflict. The professor added:
"In the multibillion-year timeline of the universe, we are all children, and we need to share the valuable possessions of our tiny enclave in the best spirit of cooperation."