The search for extra terrestrial life (SETI) is not solely the preserve of crackpots who watched a few too many episodes of the X-Files, it has been a legitimate area of research by proper scientists for some decades now. Although it may seem like the odds of success are immeasurably short people still do it because, well, to find out that ‘we are not alone’ would be the single greatest discovery we have ever known.
There are plenty of people, then, that agree we should be looking; what there is less agreement on is where to look and how to look. Given we only have a data set of 1, us, we have no way of knowing if we are utterly mundane or exceptional. So should we look for worlds like ours, medium sized rocky worlds in the so called ‘Goldilocks’ zone that allows for liquid water; is there another scenario that would be more likely to harbour life, or should we just be looking anywhere we can? Right now we just don’t know. The Drake Equation would seem to suggest that there is life out there waiting to be discovered if we can just turn over the right stone.
Last week there was a meeting of the American Astronomical Society where there was a study presented on where we should be looking for alien life. Rosanne Di Stefano argued that we should be turning our gaze upon globular clusters. This is a bit of a departure from conventional thinking if for no other reason than it’s difficult to see much of anything in a globular cluster.
As the name suggests, globular clusters are big blobs of stars. They tend to be spherical and have a very high density of stars. The nearest stars to earth are about 4 light years away but in a globular cluster the average distance between stars is only about 1 light year, nearer the core they can be as little as a few hundred astronomical units apart, that’s about the width of our solar system. Such a density of stars can make it very difficult for us to tell one star from another, they’re just too tightly packed, and so we’ve not looked in globular clusters before.
The advantages of this environment, says Di Stefano, is that they are very stable over the long term, long term being billions of years. It seems reasonable that technologically advanced civilisations would require billions of years of stability to have enough time to progress and globular clusters can provide that. All their large, hot stars burnt out long ago leaving behind an area of cooler, smaller stars that are very long lived.
Also, as the stars are so close together, hopping from one star system to the next becomes much more feasible in the hunt for resources or a new home world. It’s much easier to imagine colonising new worlds if they are only a decade away instead of thousands of years as is the case with us.
There is, however, a downside to life in a globular cluster. With stars so close together the orbits of their planets tend to be quite erratic and it is common for them to exchange planets entirely. This could certainly be enough to disrupt the evolution of life.
On top of that, because the stars are so old and stable they are amongst the oldest objects in our galaxy. That means that they are mostly first generation stars that contain little else other than the hydrogen and helium found in the early universe. All of the elements in our solar system from helium up to iron had to be formed inside very hot, very dense stars that formed, lived and died all before our own sun came into existence. Our solar system was formed from the remnants of all those dead stars.
The elements heavier than iron; things like copper, zinc, uranium and the silver and gold in your jewellery; they were all forged inside the greatest furnaces we know of: supernova explosions. Yes, we all of us have little bits of supernova inside us. So most of the elements that are completely essential for life would be all but absent from any globular cluster just because, by their very nature, the conditions for creating them simply aren’t there.
For me, this is the killer blow to this argument. Even if you can picture a world surviving for billions of years in such a hectic and dense neighbourhood there aren’t the raw materials to build even a cell, nevermind a complex, planet-hopping civilisation. And even if they were right, we would still need to overcome the problem of how we even get a proper look inside a globular cluster. These are both non-trivial problems.