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When astronomers turn to the skies in search of life on other planets, they're usually looking for places like Earth.
But with boiling deserts and subzero poles, not to mention the occasional ice age, our home isn't always the most hospitable.
"If we could change something about the Earth, what would we change?" he asked. A larger planet, for example, would have more surface area for life, and a world with more water could support more creatures.
An older place could mean more biodiversity, and one closer to other life-supporting planets could be part of an interplanetary neighborhood.
Such a planet could be like the movie "Avatar," Armstrong said, with "a more diverse life, a more intense life."
Armstrong and co-author René Heller, an astrophysicist at McMaster University in Canada, coined the term "superinhabitable" for such worlds in a paper recently published in the journal Astrobiology.
The idea runs counter to the "rare Earth hypothesis," which holds that life on Earth required an extremely precise interplay of conditions, making it unlikely elsewhere.
"We argue here in the opposite direction, and claim that Earth could turn out to be a marginally habitable world," Armstrong and Heller wrote in the paper.
"In our view, a variety of processes exists that can make environmental conditions on a planet or moon more benign to life than is the case on Earth."
Though it's unclear how many "superinhabitable" planets there could be and the closest possible candidate is 22 light-years away, the concept has gotten attention from National Geographic, NPR and social media.
Some disagree that the designation is necessary either a planet can support life or not.
Armstrong, an astrobiologist who studies planetary dynamics, welcomed the debate.
He and Heller met through NASA Astrobiology Institute's Virtual Planetary Laboratory, a community of more than 50 researchers at 20 institutions working on systems to figure out whether faraway planets are capable of supporting life.
The two scientists hope to expand the definition of what makes a planet habitable as scientific instruments become more sophisticated and the search for life beyond Earth ramps up.
"The next telescope is going to find life. It's going to happen in the next decade," said Armstrong. "However weird our theories are ... nature comes up with weirder stuff. We're just trying to be as weird as we can, to second-guess nature to see if we can be as weird as she is."