Pluto is a cold and almost certainly lifeless world right now, but that could change as the solar system ages 
ELIZABETH LAGANA/SPACE.com
It might be a few billion years before an ad like this appears in your local paper, but it could show up for good reason.
According to a new computer model designed to understand how the conditions for life might arise in unlikely places, humble Pluto and its surroundings will have warmed to downright pleasant temperatures long after the Earth has been consumed by an expanding, dying Sun.
"It's Miami Beach for millions of years, potentially longer," Alan Stern, a planetary scientist at the Southwest Research Institute, says of Pluto's future.
Stern used existing data on the outer solar system, added in the latest theoretical expectations for the Sun's evolution, and analyzed it all from a biological perspective. His results will be published in the journal Astrobiology.
The swelling Sun
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An artist's view of Pluto, today, with the dim Sun in the distance and a thin crescent moon, Charon, in the upper left. NASA/David Seal
Orbit: 248 Earth years
Time to rotate: 6.4 Earth days
Mass: 0.2% of Earth's
Diameter: 1,430 miles (2,300 km), or 18 percent of Earth's
Distance from Sun: 39.5 times as far as Earth, on average  |
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Pluto is a cold and almost certainly lifeless world right now, not a place you'd even want to visit on holiday, let alone invest in.
But that will change as the solar system ages and the tiny planet basks in a growing solar glow. In its senior years, the Sun is expected to swell to 100 times its present size and grow a thousand times more luminous, likely vaporizing Earth and the other inner planets but possibly making the outer solar system a final oasis.
The scenario might invigorate a whole swath of the solar system near Pluto, known as the Kuiper Belt, which harbors several round worlds that are a good fraction of Pluto's size, Stern explained in a telephone interview last week.
Pluto's surface presently ranges from -400 to -346 degrees Fahrenheit (-240 to -210 degrees Celsius).
The small ninth planet and its Kuiper Belt neighbors -- count among these Neptune's largest moon, Triton -- all are thought to contain ample frozen water, which when melted is one of life's essential ingredients. Observations indicate these objects also harbor organic molecules, such as hydrocarbons, that are potential building blocks for life.
"You've got all the right conditions in place for something potentially interesting to happen," Stern said. Adding warmth to the fringes of the solar system could create what he calls a Delayed Gratification Habitable Zone (DGHZ).
Added benefits
The known habitable zone now straddles Earth's orbit. Astrobiologists are eager to study the same region of space around other Sun-like stars in hopes of finding signatures of life. But in just a billion years, the Sun could be 11 percent brighter, other scientists say, rendering Earth an inhospitable greenhouse. In 5 billion years, the Sun could swell to 100 times its present size.
As the Sun expands and brightens, the habitable zone will move outward, past Mars, past Jupiter, and finally to Pluto's realm.
The DGHZ might enjoy some benefits that would encourage life, says Stern, who leads NASA's New Horizons robotic mission to Pluto and the Kuiper Belt, slated for launch in 2006. For one, the swelled Sun, officially termed a red giant, would produce far fewer harmful UV rays, known to cause injurious genetic mutations.
"Because of this, the need for a protective ozone layer around distant DGHZ worlds is greatly reduced," Stern said. Earth's high-altitude ozone layer is part of what makes this planet livable.
In addition, because Kuiper Belt Objects (KBOs) are widely dispersed, there are fewer collisions compared with the inner solar system, where Earth has been catastrophically rocked over the eons, its biology challenged several times over and possibly even forced to restart.
The big question
Being habitable is not the same as being inhabited, Stern is careful to point out. In Pluto's balmy future, life would have to either arise or arrive. No one knows which scenario was at the root of terrestrial life or how it played out.
Stern acknowledges that the DGHZ in our solar system might be only of academic interest to humans today, since its inception is so far off in time. But other stars have already evolved to the red giant phase, and their DGHZs might be places to look for signs of life, especially if icy-organic objects, like Pluto and the KBOs, are common around other stars.
"If our solar system is at all typical, then there could be billions of such systems in the galaxy today with habitable Plutos and Kuiper Belts," Stern said.
Finding DGHZs around other stars would help answer one of biology's most vexing questions: How long does it take life to arise? Here's why:
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Earth has been around for about 4.5 billion years. Firm evidence for life goes back just more than 2 billion years. But nobody knows when life began or how long it took for organic material to develop into life. It might have been spontaneous or might have been a very plodding process.
Because distant DGHZs would be hospitable for relatively brief periods -- millions to tens of millions of years -- finding some would show that life can indeed get going in a hurry.
Meanwhile, with humans not even slated for travel to Mars, it's hard to imagine mounting a crewed mission to Pluto, let alone settling down there. But when the time comes -- and if our species is still around as Earth begins to fry -- perhaps Pluto will in fact be hot property, complete with beachfront resorts. Stern said the planet could become "a low-gravity waterworld, with a distended, puffy atmosphere."
But would you really want to live there?
"I'd sure take it," he said, "given the alternative."
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