Life May Develop Even Outside The Habitable Zone

They are different now, but Earth and Venus might have been much more similar in the past. Venus: Magellan Project/NASA/JPL, Earth: NASA

Looking for life elsewhere in the universe has often been described as looking for a black dog at night. Our only light is the knowledge that life is thriving on at least one planet. When we look into the universe, Earth is the measure of all things, but maybe we need to expand our parameters.

In a new paper, published in Astrobiology, Rice University's Adrian Lenardic and colleagues suggest that we need to expand the current habitability conditions we use to search for life. The researchers think that the "Goldilocks zone" is too restrictive and that habitable planets might lie outside of it.

The Goldilocks zone is the area around stars where planets are not too warm and not too cold; the conditions are just right enough to host life. Traditionally, Earth and Venus are seen as distinct types of planetary evolution. Earth in the Goldilocks zone teems with life, while Venus (outside the habitable zone) is a deadly hell.  

The study, which is not based on extrasolar planet observations, turns this assumption on its head. Earth and Venus have many similar properties (mass, composition, and so on), and at the beginning of the Solar System, they could both have hosted life. Yes, the planets are now different, but the changes that led to the differences might have been gradual and not sudden.

“Our paper is in many ways about imagining, within the laws of physics, chemistry and biology, how things could be over a range of planets, not just the ones we currently have access to,” said Lenardic in a statement. “Given that we will have access to more observations, it seems to me we should not limit our imagination as it leads to alternate hypothesis.”

The team also argues that maybe mechanisms like plate tectonics, which are believed to be critical for life on Earth, might not be crucial. Maybe other volcanic phenomena (like the ones seen on Venus, Mars, and Jupiter's moon Io) could be equally as important.

While the paper raises an interesting point, current technology and limited resources constrain our search for alien life significantly. When future missions, like the James Webb Space Telescope, are finally able to provide a closer look at exoplanets, we will have to once again question how likely it is for life to be like us.

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