NASA/JPL-Caltech/T. Pyle (SSC)

The chemistry of a parent star can have drastic effects on the habitability of an earth-like planet.

Scientists at the University of Arizona have added another factor to consider when looking for habitable planets.  PhysOrg reported,

As a star evolves, it becomes brighter, causing the habitable zone to move outwards through its solar system. The team’s study indicates that a greater abundance of oxygen, carbon, sodium, magnesium and silicon should be a plus for an inner solar system’s long-term habitability because the abundance of these elements make the star cooler and cause it to evolve more slowly, thereby giving planets in its habitable zone more time to develop life as we know it.…

The stellar abundance of oxygen seems crucial in determining how long planets stay in the habitable zone around their host star. If there had been less oxygen in the Sun’s chemical makeup, for example, Earth likely would have been pushed out of the Sun’s habitable zone about a billion years ago, well before complex organisms evolved. Considering the first complex multicellular organisms only arose about 650 million years ago, such a move would have likely destroyed any chance of complex life taking hold on Earth.

There are probably other factors, too: “Habitability is very difficult to quantify because it depends on a huge number of variables, some of which we have yet to identify,” said the university’s assistant professor of School of Earth and Space Exploration, Patrick  Young.
Update 9/11/2012: The BBC News claims that habitable planets may be more abundant due to the fact that water can exist under the surface, even outside the habitable zone where liquid water can exist.  There are, however, constraints on how long a body’s internal heat can last.  Water is not alive; many other factors are required for life.  Even if life were possible in a deep, dark, subsurface ocean, it would not be the kind humans would be able to learn about or would want to contact.  That being so, it remains a theoretical possibility only, not conducive to observation.

Let’s tally up the factors we’ve reported so far that make the “Goldilocks Zone” more complicated than just allowing for liquid water:

  • Galactic Habitable Zone, where a star must be located (09/29/2009);….

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