Two exoplanets, once considered excellent candidates in the search for life elsewhere in the Universe, do not exist, according to a new study in the journal Science. Both non-planets, Gliese 581d and 581g, were thought to be part of the Gliese 581 star system, located only 20 light-years away.
To those familiar with the history of the Gliese 581 system, the news comes as little surprise. Claims have been repeatedly made regarding the likelihood of habitability for some planet in the system, only to see that likelihood vanish upon closer scrutiny.
Excitement about Gliese 581 first peaked in 2007 when planet c was discovered. As one of the first exoplanets found in its star's habitable zone (the region around a star where the temperature is 'just right' for liquid water to exist), planet c seemed a good candidate for life. So good that, in 2008, a high-powered digital radio signal, dubbed "A Message From Earth," was sent in the direction of planet c. (It will arrive there in 2029, and, if anyone's there to respond, we can expect a reply 20 years after that).
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