I’ve held off on posting about Gliese 581g mostly because I was waiting for the hype to die down and the “OMG aliens must exist there!” people to shut their mouths for a second. And it turns out that a skeptical view and some patience has paid off, and we all learned a lesson in how science works. Let’s look at this chronologically.
Vogt et. al. published a paper using data from the Keck I telescope about exoplanets around Gliese 581. Their data confirmed the existence of four planets previously discovered, and added two new planets to the list. One, Gleise 581F, is a large planet orbiting “far” from its star. The star happens to be a red dwarf, so far in this case is about .758 AU (1AU is the distance from the Earth to the Sun). Red dwarf stars are smaller than our own sun so the habitable zone is much closer to the star, about 1.4-1.5AU, and that is exactly where the second planet, Gleise 581g, was found. Weighing in at 3.1 Earths, it is the most probable candidate for life outside our solar system that we have found.
There are a few interesting things about this planet. First, it’s probably about twice as old as earth. Red dwarf stars tend to be very old, so there is a very good chance that the Gliese 581 system is around 10 billion years old, compared to the 4.5 billion years our planet has been around.
Second, the planet is probably tidally locked to the star, much like our moon is tidally locked to Earth (same side always faces us). This means that one side of Gliese 581g is very hot, and the other side is very cold. In between these regions of Heaven and Hell will be a Perfectly Nice Zone (I, just this very second, I dislike the term “Goldilocks zone, and have decided to replace it with the Perfectly Nice Zone). It will probably be very windy though due to the temperature difference between the two sides of this planet. I’m not sure whether being tidally locked is better or worse for the development of life. On on hand the planet has a very stable belt around it. On the other hand, this zone is relatively small. We also have no idea about the composition of the planet. It could be a giant rock with no atmosphere. It could have a thick atmosphere. The atmosphere could be toxic to us, or be perfect for us. The Perfectly Nice Zone does not bode well for intelligent life though. It’s a small space and the conditions on the rest of the planet are probably too harsh for any large intelligent species to develop.
Third, oh my what a reaction the media had to this thing. CNN quoted Steven Vogt saying that the chance this planet has life is 100 percent. Coverage can also be found in the Guardian, Wired, and the Washington Post.
My initial reaction to all of this was “Cool!” But I had my doubts about the life thing. Nothing can be 100 percent. I would say the conditions are such that life could form on the planet. It’s had plenty of time to evolve. But there is one major problem.
Gliese 581g might not actually exist.
Another group of scientists using a different data set (using observations from the last 11 years, a few years longer than the data Vogt, et. al. used) have no evidence to the existence of Gliese 581g. This is how science works. Someone produces a result (a planet!) and it needs to be verified by another group of people. In this case the data cannot be verified with existing data. So Gliese 581g might exist, but more data is needed. There could be a planet in the Perfeclty Nice Zone around a star that has its own Perfectly Nice Zone (is it catching on yet?).
One last thing. Two years ago we sent a radio signal to Gliese 581. It won’t get there for 18 years, but who knows, maybe there is life there, and maybe it’s intelligent and they have radios. It’s unlikely, but still cool to think about.