I was following the responses – on Twitter – to Matt Ridley promoting Christopher Booker’s latest piece of nonsense. In doing so, I discovered that Matt Ridley recently wrote an article in The Times, called ET hasn’t phoned, but don’t take it personally (which you can read here). It’s a reasonably interesting article, but there are a couple of things that I find a bit irritating, given my own interests.
For example, it starts with (slightly edited by me, for brevity)
…..We now know of 1,879 planets outside the solar system. A few weeks ago, we …. found Earth’s twin, a planet of similar size and a habitable distance from its sun, but 1,400 light years from here. Last week we found a rocky planet close to a star just 21 light years away, which means if anybody lives there and tunes in to us, they could be watching the first episode of Friends.
Which only underlines Enrico Fermi’s famous question, first delivered over lunch at Los Alamos in 1950 during a conversation about UFOs: “Where is everybody?” …..
The Fermi paradox gets ever more baffling, as the evidence grows of other habitable planets. The silence is beginning to seem ominous.
The implication is that we now have all this evidence for other potentially habitable planetary bodies, and yet we still seem to be alone. However, that we’ve confirmed 1879 planets outside our Solar System is largely irrelevant. Most planet detection methods are indirect; we infer their presence by determining their influence on their parent star. All we typically determine is their mass, radius, and their orbital properties. We know a little of the atmospheric properties of very hot, gas giant planets, but these are almost certainly not habitable. The silence isn’t ominous, it’s entirely expected. These planets could be teeming with life, and there is no way that we could know. If anything, the search for extrasolar planets is partly based on a desire to build a sample that we can then use in the search for extra-terrestrial life.
The Earth’s twin is really an example of an extremely poor press release. It refers to Kepler-452b, a 1.63 Earth radius planet in the potentially habitable zone of a Sun-like star. However, we have no knowledge of this planet’s mass, and there was a paper last year with the title Most 1.6 Earth-radius Planets are Not Rocky. Apparently, if you make some rather convenient assumptions about its composition, there’s about a 50% chance of it being rocky. More realistic assumptions reduce this to more like 20%. It is very probable that it is not an Earth twin. To be clear, though, the paper that presented this covered all of this very thoroughly.
I was part of the team that discovered the rocky planet close to a star 21 light years away. It’s a very interesting planet in that we have both mass and radius estimates, which indicate that it probably has an Earth-like composition. However, it is in a 3 day orbit around a star with a surface temperature 80% that of the Sun; it is almost certainly not habitable. There are 3 other planets in the system, but they too are likely un-inhabitable. In fact, the current planet detection methods are extremely successful at finding planets outside our own Solar System, but are not yet particularly good at finding those that may be habitable.
To be fair, though, I think that he was really just trying to set the scene for the rest of his article, which is about filters. These are essentially obstacles that stand in the way of life coming into existence and then evolving to become a complex, technologically advanced civilisation that could colonize the galaxy. It’s discussed in more detail in the video that I posted here. I’m in general agreement with this part of Matt’s article; I think that it may well be extremely difficult to overcome all these filters, and that it may well be possible that we’re effectively the only advanced civilisation in the galaxy.
Matt Ridley, however, finished his article with
Is it not incredibly lucky that we live on a rare planet that did make it? Well, no, because whoever lived on such a planet would say that about themselves. It is for this reason that I am not persuaded yet that the most severe filter, the one that stops most planets colonising the galaxy, comes after the stage we have reached. I think that’s unnecessary pessimism.
This seems like a classic example of Ridleyesque optimism; reasonably confident there are no more filters that will prevent us from colonising the galaxy, without really saying why (the “I’m sure it will all be fine” strategy). However, he fails to mention that climate change is a possible filter. Some might find it a little ironic that Matt Ridley is not persuaded that we will encounter any further obstacles to our colonisation of the galaxy, while being regarded by many as one of those contributing to the possibility that this will turn out to not be the case.