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Planet hunters have always been keen to find Earth's twin, but an astrobiology team now suggests that "superhabitable" planets may be even better places to look for alien life.
Since 1995, astronomers have detected more than 1,000 worlds orbiting nearby stars, sparking a race to find the one that most resembles Earth, blessed with oceans and an oxygen-rich atmosphere. That's because Earth is the only place in the universe where we know that life has evolved. (See: "More Than 1,000 Potential New Planets Found.")
In the journal Astrobiology, however, researchers René Heller of Canada's McMaster University and John Armstrong of Weber State University in Ogden, Utah, calls that idea too Earth-focused. "From a potpourri of habitable worlds that may exist, Earth might well turn out as one that is marginally habitable, even bizarre from a biocentric standpoint," they write.
Instead, they suggest that astronomers should focus their planet hunting on worlds that might harbor conditions even more amenable to life. The authors dub these hypothetical worlds "superhabitable." (See "Think Outside the Box to Find Extraterrestrial Life.")
Their report adds to a chorus of voices in the planet-hunting community that have called for rethinking the idea of "habitable zones" where worlds that follow orbits friendly to oceans and life would exclusively exist.
What characteristics might make a world superhabitable? Like all potentially habitable worlds, they should have water, agree Heller and Armstrong. But they list more than a dozen additional geological and atmospheric factors that could influence habitability.
For instance, older planets would presumably have had more opportunities for life to evolve. Larger worlds, ones up to three times as massive as Earth, might be more likely to have an atmosphere due to more volcanic activity, which releases gases.
Earth itself is thought to be located on the fringes of the habitable zone, they note, so maybe planets that are located nearer to the center of the habitable zone are more congenial to life.
Other scientists disagree about the usefulness of the concept of superhabitability. "A planet is either habitable or it's not," says atmospheric scientist Jim Kasting, who first introduced the concept of the circumstellar habitable zone, which defines a planet as habitable if it orbits its star at a distance where it's not too hot and not too cold for liquid water to form on the planet's surface.
Similarly, astrophysicist Steven Desch said that "calling a planet superhabitable is comparable to calling someone only a little bit pregnant ... Having more of what is needed for life, in my mind, doesn't make it more likely to have life."
But Ravi Kopparapu, a physicist at Penn State University, agrees with the authors that the "binary" habitable zone concept (either friendly to life or not) is too restrictive. Plenty of worlds within the habitable zone are unlikely to support life, while others—such as the icy moons of Saturn and Jupiter, which may have vast underground oceans—could potentially support life but fall outside the habitable zone. As scientists continue to discover a menagerie of exoplanets, considering more variables could help to prioritize which planets to target for follow-up.
The Goldilocks zone is between Venus and Mars, as a reference only being directly in the middle wouldn't make it more habitable.
Earth isn't a dry planet, liquid water covers 70% of the surface
At any moment, the atmosphere contains an astounding 37.5 million billion gallons of water, in the invisible vapor phase. This is enough water to cover the entire surface of the Earth (land and ocean) with one inch.
My opinion is no other planet is more habitable than ours for our type of species, we evolved with the Earth.
Let's hope we don't ruin her !
Finally and hopefully stubborn 'scientific community' is on the way to learn what thinking out of the box really means.
Thinking we know it all isn't going to get us nowhere.
Thanks for this Jade, quite the refreshment.
reply to post by muSSang
He's saying there are planets that have less terra and more aqua, with majorly different proportions than our planet. So maybe, 10% terrain, 90% surface water, and maybe oceans that are two to three times as deep.
Its a great point there could be planets with far more stable and weather systems. In fact its a garentee that somewhere a world exists like that.