The Space Telescope Science Institute suggests that there are currently 1020, or 100 billion billion, Earth-like planets in the universe, with an equivalent number of gas giants. “Earth-like” doesn’t mean an exact replica of our planet, but rather a rocky world that, if blanketed by a suitable atmosphere, would hold liquid water on its surface. Applied to the solar system, this definition would include Mars and Venus but not Mercury or the moon.
If we find just one other inhabited planet in the Milky Way, the number of other such worlds rockets up. Such a discovery, together with the unlikeliness of our galaxy being the only one to host life, would make Earth at least the 10 billionth civilisation in the universe at present. But the likelihood of any of them being identical to ours is almost zero. A change of just a millimetre in the initial conditions can result in a huge difference. Adding just one extra molecule to the early solar system could mean the Earth never formed.
Slightly counter-intuitively, the simulated solar systems end up looking quite similar, the exceptions being the simulations with no gas giants. These end up with around 11 rocky planets, most of which are less than half the mass of Earth. Add the gas giants and you get around four rocky planets ranging from half an Earth mass to a little more massive than Earth – a pretty good match for our own solar system.So even if that extra molecule had been floating about, the result wouldn’t have looked that different. “Something like Earth would probably have come up, and maybe something alive would have developed. But not us.
Don’t let this desolate randomness get you down, says Rebecca Martin of the University of Nevada, Las Vegas. “It’s exciting that we’re not special,” she says, because it means life is abundant in the universe and we can go looking for it. (adapted from an article in the New Scientist).
In this great and confusing mass of stars and planets how does God actually find us in order to encourage us, bless us and admonish us? Tomorrow I will tell you a story about this very subject. Come back and read it.
I’m quite doubtful as to the existence of other life forms, particularly intelligent life like us. A bit like God and spiritual things, I’ll only believe in it when there’s absolutely, objective evidence that it definitely exists. We can hypothesise as much as we like, but until any discoveries are made, it will be entirely guesswork. I’m also very sceptical of funding projects that try to find alien life, particularly if the funding is coming from the government. With the chances of finding life so small, I think the money could be better spend improving life here at home.