Is Earth one of a kind? In a universe of at least 40 billion galaxies, each containing perhaps 100 billion suns, it seems there would be many Earth-like planets. Yet so far science hasn't found a single one. The small number of deep-space or "extra-solar" planets that have been located by astronomers appear so drastically different from Earth that life on them is difficult to imagine. Researchers hoping to find other Earth-like worlds have been getting glum.
This isn't just a pure-science question, but one bearing on faith. If Earth were truly alone as a possible home for life, our religions--and our survival--might be all that matters in the enormity of the cosmos. On the other hand, if there are many worlds where life like ours might arise, the theological questions that trouble us here--like 'What does it mean to be made in the image of God?" and 'How does God want his creation to live?'--might become even more vexing. If other life were discovered, would humans see that as proof that life began as a random swirl of physical reactions in the universe, or would they instead say these new worlds reflect the multifaceted power and majesty of God?
Recently the outlook regarding other worlds took a big swing toward the positive. In the Big Dipper constellation, astronomers found the first distant solar system that looks more or less like ours. This hardly guarantees other life. But it increases the chance there are other Earth-like planets, and that the living part of creation may be wondrously vast.
The discovery, by astronomer Debra Fischer of the University of California at Berkeley, concerns a star called 47 Ursae Majoris, about 45 light-years away and visible to the eye in the bottom of the cup of the Big Dipper. This star has long interested astronomers, because physically it is a sister to our sun - about the same size, age and power, and most important, a "main sequence" star that, like our sun, burns at fairly steady temperatures for billions of years. (Some stars burn rapidly, erratically or with pulsating power, all presumably bad for life.) Now it turns out that spinning around 47 Ursae Majoris are two gas-giant planets similar in size and orbital location to the gas giants of our solar system, Jupiter and Saturn. And the orbit of the planets is circular, just like the orbit of planets in our solar system. That's a vital clue.
Once astronomers assumed that because our solar system is circular, others would be too. But the circular solar system, essential for life, is turning out to be the exception rather than the rule. (Now you can admonish the kids, "You didn't finish your vegetables and you don't act grateful for living in a circular solar system!") Almost every distant solar system that has been found - the count is up to about 60 so far - is "eccentric."
This means planets loop in elongated racetrack-shaped orbits that take them far from their suns for extended periods, then very close for short periods, then far out again. These worlds in eccentric orbits would experience months or years of planetary deep freeze, perhaps even close to absolute zero, followed by brief periods of boiling, sterilizing heat. For life to arise under such conditions seems inconceivable. But since planets detected around 47 Ursae Majoris move in circular paths, they will be exposed to consistent amounts of heat and light, as is Earth.