Newly-discovered alien world tops the list of closest, most Earth-like exoplanets

Wednesday, June 25, 2014, 4:31 PM - Astronomers have added yet another potentially-habitable exoplanet to their catalogues, and this one - a super-Earth planet named Gliese 832 c - now ranks as the closest of the most Earth-like planets that have been discovered so far.

In the search for planets found orbiting stars other than our own, known as extra-solar planets (or exoplanets for short), one of the biggest questions that's been asked all along is: which of these alien worlds might actually have alien beings on them?

Since we are certain that our own planet, Earth, is capable of supporting life, it has become the benchmark for answering this question, and this has culminated in what's called the Earth Similarity Index (ESI). Known as 'the easy scale' by the scientists who developed it at the University of Puerto Rico - Arecibo, it ranks planets on a scale from 0 (least like Earth) to 1 (exactly like Earth).

Currently, the highest-ranked planet on the list is super-Earth Gliese 667C c, which is one of at least six planets (three of which are in the habitable zone!) that orbit one star in a three-star system, roughly 23 light years away from us. Gliese 667C c is at the right distance from its star that it could be habitable, but it is not exactly like Earth. It is 50 per cent larger and nearly four times the mass of Earth, and it orbits a red dwarf star once every 23 days or so. So, although it is the most Earth-like planet we've found so far, these differences only give it a value of 0.84 on the Earth Similarity Index. Next down on the list is Kepler-62 e, a super-Earth with an ESI of 0.83, but it's just shy of 1200 light years away from us, so not exactly in our neighborhood of the galaxy. There are closer exoplanets, such as (unconfirmed) Tau Ceti e at 12 light years away, and Kapteyn b at 13 light years away, but they rank further down on the ESI scale.

Here's where Gliese 832 c (also called GJ 832 c) comes in. Marked as NEW on the image above, it is nearly 70 per cent larger than Earth and over 5 times its mass, and it orbits its red dwarf parent star every 36.7 days. Based on this, it ranks third on the list of Earth-like worlds, with an ESI of 0.81. However, it is also the third closest potentially-habitable exoplanet to us, at only 16 light years away. So, with its combined ESI and proximity, that makes it, according to a press release from the UPR Arecibo Planetary Habitability Lab, "the nearest most habitable world candidate so far."

Unfortunately, even though the planet's existence has been confirmed and astronomers know it's size, mass and orbit fairly well, there's no way of knowing if it really is a habitable world. It's definitely at the right distance from its star, so with the right atmosphere and a supply of water it could be capable of hosting life. However, even if it does turn out to be habitable, it would be far different there than it is here on Earth.

Given its mass, it has a higher gravity (around 18 times 1.88 times what we experience here on Earth), and thus it would likely retain a thicker atmosphere. That could work against it, as a thicker atmosphere would trap more heat, and it could be a hellish super-Venus instead of a pleasant super-Earth. As it orbits a red dwarf star, it circles around the star very close in, far closer than even Mercury travels around our Sun. It's still in that star's habitable zone, but it's close enough to the star that it would likely be tidally-locked (with one side always facing towards the star and one side always facing away), so it wouldn't have night and day like we have here. Also, rather than having an orbit like Earth's, which is almost perfectly centred on its star, the orbit of Gliese 832 c is off-centred, so it swings close to the warmer inner edge of the habitable zone for part of its orbit and then towards the cooler depths of the habitable zone at the other side of its orbit. This would give it wild seasons, and it might even swing between super-Venus and super-Earth conditions through its 36-day-long year. 

The best place for us to live there (if we could get there in a reasonable amount of time) would probably be in orbit. 

The research on this newly-reported potentially-habitable world can be read online (click here).

(Images courtesy: UPR Arecibo Planetary Habitability Lab)

(Edit: H/T to reader Chris Gibbs, who pointed out that I skipped a step in my calculations of Gliese 832 c's gravity.)