November 11th, 2015
Back on Tuesday June 25, the exoplanet newsfeed started going nuts over the release by astronomers of four new planets discovered orbiting the star system Gliese 667 (667th star system in the Gliese catalog of stars).
It wasn’t really the fact that four new planets were discovered, making the exoplanet tally around Gliese 667 C six now instead of two, but rather it was the fact that two of these new-found worlds are nicely snug within C’s habitable zone (HZ for short). This is on top of the one exoplanet that was already known to be within this same zone.
Practically overnight, Gliese 667 C went from just another star with a potentially habitable exoplanet to taking the outright lead in sheer bulk of potentially habitable worlds orbiting the same star. No other known star system to date has three possibly Earth-like planets in its orbit. Tau Ceti and Kepler 62 are tied in second, each with two.
Every other star system known so far to have potentially habitable worlds has only one such world.
Alright, so why is this so exciting?
Simply put, in the eyes of astronomers, everytime an Earth-like planet is discovered within its host star’s habitable zone, it means one more possibility that they may be able to find life thriving beyond Earth itself.
Finding absolute proof of life on another planet is one of the Holy Grails of astronomy, but more importantly answers one of our deepest questions of humanity.
“Are we alone?”
We’re almost there, though.
The first step was to find planets orbiting other stars – and we have. Nearly 1000 of them so far, with more coming every day.
The next step was to find planets that were similar in size to the Earth – and we have, thanks to the Kepler mission.
The third step was to find such Earth-like planets orbiting within their host star’s HZ – and we’ve found 12 of them so far.
The next step now is to call up people like Dr. Sara Seager to try to analyse the atmosphere of one or more of these worlds to determine the level of water vapour – a sure sign for liquid water, and of atmospheric oxygen – the smoking gun of photosynthesizing organisms (this is because free oxygen is quickly absorbed into rocks and water, thus if there is still a substantial amount of oxygen in the air when the planet has already existed for a few billion years, then as far as we know it has to be due to plants of some sort replenishing that oxygen).
With three possible Earth-like planets around Gliese 667 C, we could have a field day of discovery if all three were shown to harbour life.
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