Hopes of life on planet 'premature'

Hopes of finding a life-sustaining planet in a star system beloved by sci-fi buffs may be premature, experts believe.

The Tau Ceti system, popularised in many science fiction stories and featured in the TV series Star Trek, is known to host as many as five planets.
Two of them, Tau Ceti e and f, may lie in the "habitable" or "Goldilocks" orbital zone where temperatures are "just right" to permit surface liquid water and possibly life.
But a new study has poured cold water on the prospect of complex life flourishing around the star, one of the Sun's closest neighbours at a distance of just 12 light years.
Scientists used the chemical composition of Tau Ceti to model the star's evolution and calculate the location of its habitable zone.
Astrophysicist Dr Michael Pagano, from Arizona State University in the US, said: "Planet e is in the habitable zone only if we make very generous assumptions. Planet f initially looks more promising, but modelling the evolution of the star makes it seem probable that it has only moved into the habitable zone recently as Tau Ceti has gotten more luminous over the course of its life."
The findings suggest that planet f has probably existed in the star's habitable zone for less than a billion years.
Though this sounds like a long time, it took several hundred million years for life to emerge on Earth and more than three billion years for it to progress from simple single cells to multicellular organisms.
It took around two billion years for Earth's biosphere to produce potentially detectable changes in the planet's atmosphere.
Tau Ceti's unusual ratio of magnesium to silicon also meant that hot rock might flow more easily on its planets than it does on Earth, said the scientists. This could have "profound effects" on volcanism and tectonics, with significant implications for the survival chances of life.
Dr Pagano added: "Tau Ceti has been a popular destination for science fiction writers and everyone's imagination as somewhere there could possibly be life, but even though life around Tau Ceti may be unlikely, it should not be seen as a let-down, but should invigorate our minds to consider what exotic planets likely orbit the star, and the new and unusual planets that may exist in this vast universe."