Sunday, September 06, 2009
This idea has been written on a few times before here, but this may be the first time space.com has written a full article on the concept. The idea is very simple - we spend quite a bit of time speculating on whether various moons could have had (Titan) or do have life (Europa, Enceladus), and moons like those will naturally exist in other solar systems as well. The discovery of a Jupiter or Saturn-sized planet in another solar system has now become quite the common occurrence, but add the possibility of discovering moons to the equation and all of a sudden it's a much bigger deal. For all we know, it's also possible that the majority of extrasolar life is located in these moons instead of on planets around stars. Our solar system has a 50/50 ratio for this:
Venus - could have had life (might still have some in the cloudtops)
Earth - has life
Mars - could have had life (might still have some underground, etc.)
Titan - could have had life
Europa - might have life
Enceladus - might have life
It's also interesting to note than on average, any intelligent life located in a Jupiter-like system would have more incentive to begin exploring space than we do. We are lucky enough to have a very large moon orbiting us, but Venus doesn't, and Mars has two tiny moons. Mercury has none. That gives terrestrial planets an average of just under one moon.
Compare that to the gas giant planets that each have dozens of moons orbiting them. A civilization based on Jupiter's moon Europa would have an absolutely huge number of areas to explore in its own backyard - our Moon is 384,000 km away from us on average; well, the distance from Europa to Jupiter is only 671,000 km, still just a few days away. Also very close to Europa are Io (421,000 km from Jupiter), Ganymede (1 million km), and Callisto (1.8 million km), plus, oh, another 59 more moons. Imagine having 63 places to send a probe right in your own backyard.
Not to mention how difficult it would be for early civilizations to conclude that the universe was heliocentric when the planet you orbited was always locked in the same position in the sky (and huge).