This is an essay I wrote in response to the question “What are the prospects of finding life on other plantets?”. It was entered into the RCSU Science Challenge 2010, an essay competition hosted by Imperial College London, and was shortlisted for a prize.
Since we stopped believing we were at the centre of the Universe, humans have looked up to the stars and wondered if they truly are alone. Some say it would be foolish, arrogant even, to say so, but we have no evidence to the contrary.
The Drake equation gives an estimate of the number of civilisations in the Universe with the ability to communicate with us. It starts with the rate of star formation and multiplies this by the fraction of stars that have planets, then the fraction of planets capable of supporting life and so on. Current estimates using this equation suggest that there should be at least a handful of other civilisations out there capable of communication. Not one has yet announced themselves. The contradiction between this high probability of intelligent life and our lack of contact with them is known as the Fermi Paradox. Over the years there have been numerous ways suggested to resolve this paradox, but none are as satisfying as we imagine contact with another civilisation would be.
So far, our attempts to communicate with other worlds have been in vain. Some say we’ve not been really been trying; mostly, we’ve been sitting tight and patiently waiting for someone to contact us. In fact, one solution to the Fermi paradox says that we have not made contact with other civilisations simply because everybody is listening for messages, but nobody is transmitting any. Even our attempts at active communication have been somewhat futile. For example, the Arecibo message, beamed to a star cluster known as M13 in 1974 will take 25,000 years to reach its destination. By this time M13 will be long gone. Maybe it’s time to put a bit more effort in.
Gliese 581d is an extrasolar planet orbiting a star in the constellation of Libra. It’s a super-Earth with a mass roughly eight times that of our planet, and it resides in the Goldilocks zone around its star; the zone which is not too hot or too cold, but just the right temperature for life. Scientists have studied this planet and found that it has an atmosphere just inside the parameters of being capable of supporting life. The Darwin Mission, deferred indefinitely in 2007, would have had the capacity to detect what mix of O3, H2O and CO2 is present in Gliese 581d’s atmosphere. If found in the correct proportions, these “biomarkers” would be the smoking gun of life; they would indicate that photosynthesis is occurring on the planet. If there was to be an interstellar mission, Gliese and its super-Earth would be first in line for exploration.
Let’s say that these biomarkers were found and an interstellar mission proposed. What next? Well, we’d need to work out a way to travel the 20.3 light years to the star system. While this is not a large distance on a cosmological scale, it would certainly pose us a serious challenge. Huge leaps forward in technology would be needed to reach speeds of only 10% of the speed of light. The method most likely to be capable of achieving these speeds in the future is nuclear pulse propulsion, i.e. using nuclear explosions to provide thrust. But even with this technology it would still take around 200 years to reach Gliese. Barring major medical advances in that time, the people who waved the rocket off on Earth would not even live to see it reach the halfway point! And let’s not forget the time delay in sending and receiving information from it.
So, 200 years. The best candidate for that sort of distance is a von Neumann probe, named after mathematician and physicist John von Neumann who studied self-replicating machines. The probe would use raw materials found along the way to make copies of itself, enabling it to travel vast distances to far away star systems without needing a vast payload.
The probe would also need a high level of artificial intelligence in order to look after itself, to monitor the world it encounters and to determine what actions to take as it goes along. For instance, if the culture found was deemed advanced enough to communicate with, the probe would need to make itself known and then speak on our behalf. If, however, communication was deemed dangerous, it would need to hide.
An interstellar mission is not yet a possibility for us, but it will be in the future. However, the Universe is a big place. Who’s to say that there isn’t another civilisation out there, who had a similar bright idea a good few years ago after monitoring the atmosphere of a promising looking planet orbiting a star quite a lot like our Sun? Maybe the prospects of finding life, or at least technology, from another world aren’t so dim after all…