Gleise 581c: what do you mean, ‘far away’?

Some people are putting a downer on the exciting news that a planet where water could exist as a liquid has been discovered orbiting Gleise 581, saying that 20.5 light years is a long way away. I’d like to put a positive spin on this.

OK, so it’d take us a million years to get there with current spacecraft, and the problems would start before you even passed the Moon – but think positive! After only a few years of looking (the first extrasolar planet was only observed a decade or two back) we’ve found a ‘Goldilocks zone’ planet, i.e. one where life could conceivably exist, just twenty light years away.
Cosmically speaking, that’s the flat next door.

And far from being bad news, it’s reasonable evidence that the universe is teeming with planets potentially supporting some form of life, even according to our narrow definition of ‘life needs water’. That’s the exciting bit.

Let’s run some numbers. The new planet is one of about 100 stars within 20 light years of us. In other words, even with our present primitive detectors, we can find two planets (our’s and Gliese’s) in a sphere just 40 lightyears in diameter.

Now the main chunk of the Milky Way is about 100,000 light years across and 1000 thick. That’s a volume of around 2 trillion cubic light years in the ‘core’. With candidate planets every 20 light years, that’s 250 million candidate planets in our galaxy alone! And that’s a worst case scenario.

There are 240 billion observed galaxies in our universe. Each galaxy with, perhaps, a minimum 250m more ‘habitable’ worlds. That’s 60 million trillion (that’s 6 followed by 19 zeroes) planets bearing some comparison to warm, life-spawning Earth.

And if the many-worlds interpretation of quantum physics is right, raise all that to the power of infinity minus 1….

The Universe is still amazing, even if we don’t get out much.

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