Sun\'s closest neighbor could harbor \'superhabitable\' world

The sun's closest neighbor star may host a "superhabitable," life-supporting world of islands, shallow seas and gentle slopes, Canadian scientists say. Researchers at McMaster University in Ontario, conducting a detailed analysis of what might make planets suitable for life, say Alpha Centauri B, the star closest to the sun, would be the perfect star to host such a planet. While most scientists assume the best places to look for alien life are Earth-sized planets orbiting sun-like stars, the researchers said, current models for habitability consider only a few criteria -- such as a planet's size and distance from its star -- limiting the search to rocky worlds like Earth in orbits similar to our own. "But no one had ever touched the question of whether other places may be even more benign environments than Earth provides," astrobiologist Rene Heller told NewScientist.com. Heller and his colleagues analyzed a number of additional criteria, including a hypothetical planet's gravity, age and internal structure, to explore the possibilities of a "superhabitable" planet. The analysis suggests the choicest locale for life could be a world slightly bigger than Earth orbiting an orange star slightly smaller than the sun, they said -- like Alpha Centauri B. "You want to have a host star that can keep a planet in the habitable zone for 7 [billion] to 10 billion years," enough time for ecosystems to reach an optimal state for diverse life to flourish, Heller said. Alpha Centauri B is about 6 billion years old, which means life on a superhabitable planet in orbit around it would have an evolutionary head-start over life on Earth, Heller added.