Gliese 581 is a red dwarf star in the Libra constellation that is roughly 20.3 light years away from Earth. As the 87th closest star system to our sun, 581 did not garner much attention until recently, when two earth-like planets were discovered to be orbiting it. These planets fall into the habitable, or ‘Goldilocks,’ temperature range, marking a possible opportunity for exosolar (beyond our solar system) habitation.

“There are four factors at play when you are considering whether a planet is earth-like,” said Assistant Professor of Physics Don Smith. “The mass (or equivalently, size) of the planet, its composition (what elements are present — is it a rock, like Earth, or is it a ball of gas, like Jupiter? Is there water?), how far it is from the star, and how hot the star is. We presume that to have life, certainly to have life like us, you need to have liquid water on a solid surface.”

Gliese 581c, the first of five planets orbiting 581 to be considered possibly habitable, is at a proper distance from the star to potentially have liquid water and retain a temperature that could sustain forms of life which exist in physically or chemically extreme climates, much like a select few organisms here on Earth.

However, according to extrasolar astronomer Steven Vogt’s initial report on the planet, its atmosphere is composed in such a way that it creates a more powerful variation on the greenhouse effect, ultimately making it too hot.

But just another few light years away, within the habitable zone of its parent star, a planet with a mass 3 to 4 times that of Earth (indicating a solid surface) known as Gliese 581g also demonstrates life-harboring characteristics.

The report on 581’s surrounding planets identifies a dense atmosphere around 581g, more capable of circulating heat, as well as a global equilibrium temperature around -64 to -45 °C, which is not too far from Earth’s -18 °C.

Yet despite these factors indicating habitability, there are important differences between 581g and Earth. For instance, Vogt notes that the planet never rotates because of how close it is to the star that it orbits, much like our moon. As a result, one hemisphere gets constant light from 581, while the other faces away in darkness. This is also known as being tidally locked.

So what is the likelihood that we will actually find anything living on Gliese 581g?

“Pretty high actually,” said biology department chair, Melanie Lee-Brown. “I would imagine simple unicellular or colonial organisms. It would look like our Archaea bacteria (single-celled and able to live in extreme environments).”

As a result of the high probability of life on the planet and the speed with which it was discovered, some believe that this could indicate many more nearby planets capable of sustaining life.

Vogt writes that, “(The) mere fact that a habitable planet has been detected this soon, around such a nearby star, suggests that (the percentage of stars with Earth-like planets) could well be on the order of a few tens of percent, and thus that either we have just been incredibly lucky in this early detection, or we are truly on the threshold of a second Age of Discovery.”

“Note that Vogt is not saying we ‘are’ on the verge of a ‘second age of discovery,’ but that we ‘may’ be,” said Smith. “I assume he’s referring to the time since the discovery of the first extra-solar planets in 1995 as the first age. I don’t see why we need to declare that ‘age’ over and a new one beginning. Maybe I don’t know enough about it to see why this is so much different, but it feels to me like the same exciting process is still going on.”

Ultimately, the discovery of both of these new planets has contributed greatly to our understanding of the universe.

“The important aspect of all this is not whether it’s a second age or a first age or whatever; it’s that human ingenuity, assisted by technology, has got us to the place where a question: ‘are there (inhabitable) planets around other stars?’— (a question) that has been the realm of speculative fiction for the entirety of human history — is actually being answered,” said Smith. “With that question down, the Big One, ‘is there life elsewhere in the universe,’ doesn’t seem so far-fetched any more.”