Wednesday, October 06, 2010
The discovery of Gliese 581g (also Zamina, its preliminary nickname) has led to a lot of discussion on just how far 20 light years is. You might notice the number 180,000 in a few articles, which is the number of years it would take to reach there at the current velocity of the fastest probe we have at present. This number is not just useful for debunking claims that the planet is "right next door" as some have said, however. Let's take a look at some simple facts.
Fact: 180,000 years at 20 light years works out to 38700 years for even the closest destination, Alpha Centauri. Even a brown dwarf discovered at a distance of just one light year would then take 9000 years to reach. These numbers, however, assume plain old chemical combustion as our source of propulsion and if we had to send a probe out tomorrow, at the very least we could send out an ion-powered one, and in a few more years one powered by VASIMR. The only real method of propulsion that could do the job, however, is probably antimatter propulsion. That leads us to our next fact:
Fact: there are about 60 individual stars within 16 light years of us, and adding brown dwarfs to the mix we will probably end up with a few hundred, maybe 300 or so. In comparison, the entire Milky Way galaxy has about 200 billion stars. This is important because:
Fact: life as far as we know it works like this: it springs up in a few hundred million years, then spends a few billion years in an extremely simple state, then begins to evolve at greater and greater rapidity until finally highly intelligent life and civilization emerges. (How long such civilizations last on the average is another matter) This means that even if life is common it's most likely that simple life will be the easiest to find, and complex/intelligent life may not exist anywhere near us. And even if we develop the ability to travel to other stars within a few decades...
Fact: receiving signals from any of these missions will take years. Even after the decades it would take to get there, we would not learn about conditions at Gliese 581g until 20 years after the mission has arrived. 20 years is a lifetime when it comes to the development of technology. And finally:
Fact: a mission to any star would be extremely expensive, and at most would result in information on one star system only.
So what does this mean? Very simple: we need to do three things. 1) Spend a lot more money on telescopes, 2) begin to explore our own Solar System, 3) begin working on more advanced forms of propulsion in preparation for later.
2) even though it's a bit sad that these new planets are all so far away, keep in mind that our own solar system is still full of possibilities. We just found out last year that the Moon creates its own H2O, life could be present in the cloudtops of Venus, Mars, Europa and Enceladus, and we haven't even been more than 400,000 km from our own planet yet. There's lots to do in our own corner of the galaxy for the time being.
3) new forms of propulsion will need to be developed as yes, eventually we will want to start sending people to explore these planets. Thanks to 1) we will know a fair bit about them even before we arrive, and thanks to 2) we will be more confident in doing so. If we are lucky then we will find something interesting around a nearby brown dwarf (a planet in the habitable zone of one of these, which could exist outside the Roche limit according to this paper on pdf) and that will become our first destination. At a (relatively) close distance of a light year or two, the travel time for radio signals to and from there will at least be bearable. We may instead send a probe with advanced AI to check out the system without needing to be run by humans, but if the planet(s) orbiting the brown dwarf turn out to be really interesting we will be driven by an urge to see it ourselves.
So in short, we need bigger and better telescopes, and the more of them we build the more we will know all about these new planets right now. Not in the next decade or two, now.