Recent studies of the Edgeworth-Kuiper asteroid belt reveal the “amazing circumstances” required to make our solar system a suitable place for life.1 The belt itself is a recent discovery. It consists of thousands of asteroids orbiting beyond Neptune. In January 2000, an international team of astronomers recognized that the orbits of these asteroids faithfully record our sun’s close encounters with other stars over the past 4.6 billion years.
All the star-planet systems discovered so far represent extremely hostile environments for life. GAS GIANTS such as Jupiter lack the capacity to support life.
Until recent months, all the positively-identified planets outside our solar system (18 thus far) have been observed to orbit alone around one or two stars.2 Such planets bear little resemblance to our own and, thus, do little to support the case for extraterrestrial life. Things changed, however, in April of this year. Astronomers reported the discovery of multiple planets orbiting a hydrogen-burning star.3 In other words, they found a planetary system apparently similar to our own.
That news made headlines worldwide. It was broadcast as potent evidence for life's abundance in the cosmos. Additional momentum for the media stir came from reports that the parent star in this system, Upsilon Andromedae, is only a "little" younger, no more than a billion and half years younger, than the sun. All the other extra-solar planets are orbiting much younger (thus less stable) stars.
As exciting as this recent discovery is to the astronomical community, we must say that the resemblance between the two solar systems has been exaggerated.4,5 The three planets discovered are all "gas giants," the smallest at least 70% as massive as Jupiter, 225 times more massive than Earth. All three have drifted from wherever they formed toward the star, Upsilon Andromedae. The drift of such giants would radically destabilize the orbits of any other planets in the vicinity, including any with the hypothetical capacity to support life. Such hypothetical life could not survive such bouncing.
The smallest of the three planets has drifted so close to the star that it orbits seven times closer to the star than Mercury does to the sun - not a hospitable life zone. Neither is the neighborhood of the larger two, which exceed Jupiter's mass by double and quadruple (670 and 1500 Earth masses), respectively. We observe that their orbits are highly elliptical, i.e., elongated like a stretched rubber band. This orbital pattern again means instability for any nearby planets, thus no capacity for life support anywhere in the system.
One team of astronomers concludes that the system would tear itself apart within a million years or so.6 (If the planets are more massive than their proposed minimums, more rapid disintegration would result.) The planets may not even be indigenous to Upsilon Andromedae. Some evidence suggests that one or more of the three may have been captured (by the star's gravity).
From my perspective, the Upsilon Andromedae system demonstrates the uniqueness of our solar system. All the star-planet systems discovered so far represent extremely hostile environments for life. By contrast, our system seems "made for life" in every detail.
by Dr. Hugh Ross assisted by Guillermo Gonzalez