Astronomers have a mind-blowing new theory: that there are 17 billion Earth-sized planets in our galaxy. They don't yet know how many of these worlds are in habitable zones, but the implications of this discovery are amazing. So much that some claim the "quest for a twin Earth is heating up".
Simply put: If there are 17 billion Earth-sized worlds In our galaxy, it's clear that the universe is bubbling with life.
The team, lead by Francois Fressin of the Harvard-Smithsonian centre for Astrophysics, used the latest data from NASA's Kepler mission to find that one in six stars have "a planet 0.8-1.25 times the size of Earth in an orbit of 85 days or less".
Of course, before we start with this alien life maths wankfest, let's answer a fundamental question: why are Earth-sized planets important? The answer is simple: Earth is the only habitable planet that we know of. Scientists assume that, given the same set of conditions — orbit time, distance from sun, gravity and composition — life will develop in other star systems just like it developed in Earth. Simplifying (and without knowing yet why this is exactly), planets like Mars weren't big enough and planets like Venus were too close.
Now, let's be really conservative and assume that only one per cent of those planets is in its star system's habitable zone. That's 170 million Earth-sized worlds that may harbour some kind of life.
Let's keep being sceptical. Let's say that only one per cent of those planets have actually developed actual life. That leaves us with 1.7 million worlds bubbling with lifeforms.
It's most probable that these worlds would have a variety of organisms but, continuing to be pessimistic, let's suppose that only one per cent of those Earth-sized worlds have developed complex animals. That's 17,000 alternative Earths full of three-headed monkeys or whatever.
Finally, let's presume that one per cent of those planets' animals have evolved so much that they have developed a civilisation similar to ours. That's 170 worlds, people. 170 worlds is one amazing number, at least for me.
Life in the Universe
Now, if that's not amazing to you, look at the number of galaxies in the universe. The most recent computer simulation puts that number at 500 billion. Of course, not all galaxies have the same numbers of stars, but since some are bigger than ours and some are smaller that ours, let's just assume that it all evens out. Wait. Let's be galactic jerks here and take 100 billion galaxies out of the total number. 400 billion galaxies, each of them with about 170 civilised worlds.
That's 79,900 billion planets with civilisations on them.
Read that number a couple of times.
Of course, the universe is an awfully big place. So big that we may never encounter another civilisation. But that's a minor point. The fact is that, even being conservative, even if we further cut that number drastically, even if we assume much lower percentages, even if we think that some civilisations may have been destroyed by asteroids or wars or some other kind of disaster — even if we just assume that, out of those 79,900 civilisations, only one per cent have actually survived and thrived, that leaves us with 799 billion civilisations in the universe.
Still too optimist for you? Destroy 99 per cent of those with Death Star lasers. That's still 7.99 billion civilisations.
Going one step further, think about the chances of meeting one of these civilisations. Let's presume that only one per cent of the 7.99 billion have mastered warp drives — Not a crazy possibility!
Oh, and all of this is assuming that only planets similar to ours can harbour life. The fact is, we really don't know that that is the case.
But given what we do know, knowing how life seems to thrive in the most desolate environments and looking at these extremely negative scenarios, there's really no other conclusion: We are just one of many. And when this whole thing makes my head spin, that's good news. We are not alone.
I have no doubt that the encounter is inevitable. We just have to survive long enough. But we will get there.
Read the summary of their paper at the Harvard-Smithsonian centre for Astrophysics.