We often start with the assumption that Earth, our Sun, and our entire solar
system is fairly typical. But as we learn more about the universe, we begin to look odd. The Kepler Space Telescope sees star systems containing planets that are fairly similar in size with regular orbital spacing.
By contrast, our own solar system has a range of planetary sizes and distances between neighbors. The smallest planet, Mercury, is about one-third the size of Earth — and the biggest planet, Jupiter, is roughly 11 times the diameter of Earth. There also are very different spacing between individual planets, particularly the inner planets. space.com
We have a lot to learn about how solar systems form, and who knows what the current research may mean for the possibility of life in other star systems. Or closer to home, where oceans beneath the frozen surfaces of Jupiter’s and Saturn’s moons may be the best places to search for extraterrestrial life.
The Kepler study reminded me of an old book, (published in 2003, which makes it very old in the field of exoplanets) Rare Earth. Even without the latest exoplanet data, the authors knew that our Sun is uncommonly rich in heavy elements, and that Earth orbits in a narrow habitable zone and has an oddly large moon. Plate tectonics have formed and reformed Earth but not our neighbor Mars. Global catastrophes from a frozen Snowball age to the asteroid that destroyed the dinosaurs make life on our blue globe seem remarkably lucky.
Rare Earth is still worth reading. On Amazon, the book is popular. Some reviews complained the authors “seem to feel the reader needs the same information endlessly repeated.” Or that, while the authors demonstrate that earthly life could have evolved nowhere else, they don’t consider that life on other worlds may be very different.
That reflects a problem all exobiology struggles with – we only have one example of life. Maybe earthly life is rare but life-in-general is common.
ET is a fascinating subject. Maybe, in our lifetimes, science will find something swimming beneath the frozen surfaces of Jupiter’s or Saturn’s moons. Maybe, someday, something from out there will find us, swimming in the atmosphere that covers our planet. The possibilities are too compelling to ignore. Keep searching, astrobiologists. Keep searching, and let us know what you find.