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takyon [soylentnews.org] writes:

[linked study is currently unavailable. find DOI]

A new study suggests that "habitable zones" may not be habitable for long [theconversation.com]:

In research published [bit.ly] in the journal Astrobiology, we argue that early extinction could be the cosmic default for life in the universe. This is because the earliest habitable conditions may be unstable. In our "Gaian Bottleneck" model, planets need to be inhabited in order to remain habitable. So even if the emergence of life is common, its persistence may be rare.

Mars, Venus and Earth were more similar to each other in their first billion years than they are today. Even if only one of the planets saw the emergence of life, this era coincided with heavy bombardment from asteroids, which could have spread life between the planets.

But about 1.5 billion years after formation, Venus started to experience runaway heating and Mars experienced runaway cooling. If Mars and Venus once harboured life, that life quickly went extinct. Even if wet rocky Earth-like planets are in the "Goldilocks Zone [abc.net.au]" of their host stars, it seems that runaway freezing or heating may be their default fate. Large impactors and huge variation in the amounts of water and greenhouse gases can induce positive feedbacks cycles that push planets away from habitable conditions.

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