Before you ask, yes I have been talking about Gliese 581g a lot lately. I promise that I’ll stop after this, OK? Good.

Now, to the topic at hand. As most of you already know, I decided to do a study on how life could survive on Gliese 581g. The first thing I started with is the so called “shaper” of life, gravity. Without gravity, we’d all float into space and life could not exist. Too much gravity, and we’d be short, stocky little guys that have immense muscles strength. Too little, and we’d be tall, scrawny, and very light. I wanted to find out the surface gravity of Gliese 581g to find out if they’d be the former or the latter. To do so, I used Issac Newton’s universal law of gravitation, which states that g=G(m/r^2) where:

  • g is the surface gravity of Gliese 581g
  • G is the gravitational constant of 6.67428*10^-11
  • m is the mass of Gliese 581g, which is 3.1 to 4.3 Earth masses. I decided to choose the smaller estimate, so 3.1 Earth masses converted into kilograms is 1.851847*10^25
  • r is the radius of Gliese 581, which is between 1.3 and 2.0 Earth radii. Because I choose the smaller estimate for the mass, I choose the smaller for the radius as well. 1.3 Earth radii converted to metres is 8.2915781*10^6

When I plug these into the equation, I get an equation of:

g=6.67428*10^-11((1.851847*10^25/(8.2915781*10^6)^2)

After accounting for all the different units, the answer comes out to be

g=17.97774156 metres/second^2

This means that if I were to drop an object on Gliese 581g, it would fall at a rate of about 18 metres every second. By comparison, the surface gravity is around 9.81 metres/second^2 here on Earth, making Gliese 581g have a gravity around 1.8 times stronger. While this may seem like a lot, it really isn’t. If we were to visit Gliese 581g, we would be able to stand up on the planet without much struggle and walk around. Within a few years, our muscles would adapt to the new gravity and we wouldn’t even notice the difference. What this means for life on Gliese 581g is that, at least as far as gravity is concerned, it would develop in much the same fashion it did here.

While the gravity on Gliese 581g is similar, the environment sure isn’t. Gliese 581g, because it is so close to its host star, is tidally locked, much like our moon. This means that one side is eternally basked in sunshine while the other is deprived of it for all of time, meaning there are no days on Gliese 581g. Because Gliese 581g doesn’t rotate, it has no axial tilt which means no seasons, either. While scorching heat and dreadful cold may seem to be harsh conditions for life to develop, we can see that even on our own Earth many small microbes survive in both. 

However, we aren’t looking for microbial life; while it would be nice to find, we want life as we know, animals, plants, and maybe even some form of intelligent life. There is a place where these things could develop on Gliese 581g: along the Terminator line that separates night from day. In this area, it would eternally be twilight, giving it the nickname of the “Twilight Zone.” In the Twilight Zone, Earth like temperatures could exist. Imagine a fertile band spanning the entire planet separating a desert from the Arctic, and that is what Gliese 581g is probably like. 

If the atmosphere is stable enough on Gliese 581, which in all likelihood is, it would convey heat around the planet from the hot side to the cold side, somewhat equalizing the heat and making more parts of the planet habitable for Earth-like life. Likewise, cold air from the cold side would circulate to the hot side, stabilizing the temperatures. The chances of life existing on Gliese 581g are actually very good. It has been around much longer than our own planet, so there’s much more time for life to develop. And we have seen that anywhere there is water on Earth, there is life. There is billions upon trillions of gallons of water in the universe, and Gliese 581g probably has some. If that is the case, then life must surely exist on Gliese 581g.

What would intelligent life on Gliese 581g look life if it existed? I picture a species that may rely on photosynthesis for energy instead of consumption, considering the areas where they could inhabit would be basked in eternal sunshine. They would be resistant to heat, letting them roam the desert side of the planet as they wish. However, they would have to return to the Twilight Zone for liquid water unless they find a way to irrigate the desert and put water there without it evaporating. If these lifeforms occasionally drift over to the night side, they would easily be able to spot our star among the mosaic of stars across the sky without the need for a telescope. They could be gazing upon our star wondering the same thing we ponder about endlessly: is there other life out there?