In September 2010, the planet-hunting team of Steven Vogt made headlines by announcing that they believed they had discovered the most Earth-like planet ever: Gliese 581g, a small planet orbiting squarely in the habitability zone of its red dwarf star, Gliese 581. The reception of this discovery has been uncertain. Some scientists seem uncertain it exists at all. But one, Australian SETI researcher Ragbir Bhathal, is going in the other direction. Bhathal says an anomalous light pulse picked up by SETI in 2008 could actually have come from Gliese 581g – making this a potential first-contact scenario.
Gliese 581g, according to the coverage of its discovery, is the seventh planet discovered in the Gliese 581 star system. It is less than twice the size of Earth, and orbits one-sixth the distance from Earth to our own Sun. However, Gliese 581 is a relatively cool red dwarf star, so that the conditions could actually be very similar. This does not necessarily mean that Gliese 581g is exactly like Earth. For example, at that distance it would be tidally locked, meaning that the same side always faces the Sun. (The same process affects our own Moon, which is why we always see only one side of it from the surface of the Earth.) One side of Gliese 581g would therefore be extremely hot, the other side would be extremely cold and dark, and a relatively thin band running around the planet between these zones might potentially be warm and welcoming. This did not stop Vogt from coming out with an optimistic, unsupported, and possibly ill-advised claim that there was a “100% chance” of life on Gliese 581g.
Life is not intelligent life, however – and every current search for life within our solar system assumes that all we are likely to find is extremely primitive, single-celled organisms. Bhathal thinks we might find more on Gliese 581g, though. In 2008, he says, his team detected a “very sharp signal, sort of a laser lookalike thing” – something which you would not expect to be emitted from a natural source. They were unable to find any repeat signals on subsequent scans, but the chance discovery has become interesting again now, because it appeared to come from the same region of space as Gliese 581.
Not everyone is convinced. Frank Drake, a SETI pioneer and the inventor of the important Drake Equation (an estimate of the number of intelligent species in the galaxy), says he’s “very suspicious” about Bhathal’s announcement. Still, Gliese 581 is a tempting target because of its relative proximity to Earth at just 20 light-years. This means the signal we just received, if indeed it came from Gliese 581g (and if indeed it ever existed), would have been sent in 1990. If we sent a response and there was someone there to hear it, they would receive that response in 2030. This may seem like a long time to wait, but many other stars considered good candidates for extrasolar planets are hundreds of light-years away or more.