If things don't work out on this planet...
Or if our itch to explore becomes unbearable at some point in the future...
Astronomers have recently found out what kind of galactic real estate might be available to us.
We'll have to develop advanced transport to land there, 20 light years away.... But that's for later.
The question right now: is it worth the trip? The destination is a star that you can't see with your naked eye, in the southern constellation Libra, called Gliese 581.
Identified over 40 years ago by the German astronomer Wilhelm Gliese, it's a red dwarf with 31% of the Sun's mass... and only 1.3% of its luminosity.
Until recently, the so-called M Stars like Gliese 581 flew below the radar of planet hunters.
They give off so little energy that a planet would have to orbit dangerously close just to get enough heat.
Now, these unlikely realms are beginning to show some promise... as their dim light yields to precision technologies...
...as well as supercomputers... honed in the battle to understand global changes on this planet... Earth.
Will we now begin to detect signs of alien life?
Or will these worlds, and the galaxy itself, turn out to be lifeless... and Earth, just a beautiful, lonely aberration?
To some, like astronomer and author Carl Sagan, the sheer number and diversity of stars makes it, as he said, "far more likely that the universe is brimming over with life."
This so-called "many worlds" view can be traced back to ancient observers... in China, India, Greece and Egypt. The Qur'an, the Talmud, and many Hindu texts all imagined a universe full of living beings.
In the 16th Century, this view got a boost from astronomer and mathematician Nikolas Copernicus... who came to believe that Earth is not the center of the universe, but revolves around the Sun.
Seven decades after Copernicus, Galileo Galilei used his newly developed telescope to show that our Sun was just one among countless other stars in the universe.
By the modern era, the "many worlds" view held sway in scientific circles. A variety of thinkers considered what and who inhabited worlds beyond our own.
From Martians desperate to get off their planet... to alien invaders intent on launching pre-emptive strikes against ours... or simple life forms on an evolutionary track to complexity.
But other thinkers have been struck by a different view.
The Greek philosophers Aristotle and Ptolemy believed that humans and Earth are unique.
With the spread of Christianity, this Ptolemaic system became widely accepted.
The latest variation on this theme is what's called the "Rare Earth" hypothesis. It holds that Earth and sophisticated life were the result of fortuitous circumstances that may not be easy to find again in our galaxy.
Does the current search for planets shed light on this debate... sending it in one direction or the other?
So far, our only good reference for recognizing an Earth-like planet is... Earth.
It does have some fortuitous characteristics... it's dense, it's rocky -- with a complex make-up of minerals and organic compounds -- and it has lots and lots of water.
It's also got a nearly circular orbit around the Sun, at a distance that allows liquid water to flow... not too close and not too far away, in the so-called "Habitable Zone."
That's defined as the range of distance from a parent star that a planet would need to maintain surface temperatures between the freezing and boiling points of water.
Of course, that depends on the size of the planet, the make-up of its atmosphere, and a host of other factors.
And whether the parent star is large; medium like the Sun; or small.
Some scientists also believe we live in a "Galactic Habitable Zone." We're close enough to the galactic center to be infused with heavy elements generated by countless stellar explosions over the eons...
But far enough away from deadly gamma radiation that roars out of the center.
If there is a galactic habitable zone... it's thought to lie 26,000 light years from the center... about where we are... give or take about 6,000 light years.
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Is our galaxy filled with life? Or is Earth a beautiful, lonely aberration? Astronomers are rapidly discovering planets orbiting other stars. Will any be worth exploring up close? Could humans – or whatever we become – live there someday?
Credit: SpaceRip / SPACE.com - Tom Lucas & Dave Brody