The Search For Earth-Like Planets

The search for Earth-like planets is reaching a fever-pitch. Does the evidence so far help shed light on the ancient question: Is the galaxy filled with life, or is Earth just a beautiful, lonely aberration? If things dont 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. Well have to develop advanced transport to land there, 20 light years away. The question right now: is it worth the trip?

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.

At Least 100 Billion Planets Populate The Galaxy

That's the conclusion of a new study by astronomers at the California Institute of Technology (Caltech) that provides yet more evidence that planetary systems are the cosmic norm. The team made their estimate while analyzing planets orbiting a star called Kepler-32—planets that are representative, they say, of the vast majority in the galaxy and thus serve as a perfect case study for understanding how most planets form.

"There's at least 100 billion planets in the galaxy—just our galaxy," says John Johnson, assistant professor of planetary astronomy at Caltech and coauthor of the study, which was recently accepted for publication in the Astrophysical Journal. "That's mind-boggling."

"It's a staggering number, if you think about it," adds Jonathan Swift, a postdoc at Caltech and lead author of the paper. "Basically there's one of these planets per star."

The planetary system in question, which was detected by the Kepler space telescope, contains five planets. The existence of two of those planets have already been confirmed by other astronomers. The Caltech team confirmed the remaining three, then analyzed the five-planet system and compared it to other systems found by the Kepler mission.

The planets orbit a star that is an M dwarf—a type that accounts for about three-quarters of all stars in the Milky Way. The five planets, which are similar in size to Earth and orbit close to their star, are also typical of the class of planets that the telescope has discovered orbiting other M dwarfs, Swift says. Therefore, the majority of planets in the galaxy probably have characteristics comparable to those of the five planets.

While this particular system may not be unique, what does set it apart is its coincidental orientation: the orbits of the planets lie in a plane that's positioned such that Kepler views the system edge-on. Due to this rare orientation, each planet blocks Kepler -32's starlight as it passes between the star and the Kepler telescope.

By analyzing changes in the star's brightness, the astronomers were able to determine the planets' characteristics, such as their sizes and orbital periods. This orientation therefore provides an opportunity to study the system in great detail—and because the planets represent the vast majority of planets that are thought to populate the galaxy, the team says, the system also can help astronomers better understand planet formation in general.

To do that calculation, the Caltech team determined the probability that an M-dwarf system would provide Kepler-32's edge-on orientation. Combining that probability with the number of planetary systems Kepler is able to detect, the astronomers calculated that there is, on average, one planet for every one of the approximately 100 billion stars in the galaxy. 

But their analysis only considers planets that are in close orbits around M dwarfs—not the outer planets of an M-dwarf system, or those orbiting other kinds of stars. 

As a result, they say, their estimate is conservative. In fact, says Swift, a more accurate estimate that includes data from other analyses could lead to an average of two planets per star.

M-dwarf systems like Kepler-32's are quite different from our own solar system. For one, M dwarfs are cooler and much smaller than the sun. Kepler-32, for example, has half the mass of the sun and half its radius. The radii of its five planets range from 0.8 to 2.7 times that of Earth, and those planets orbit extremely close to their star.

The whole system fits within just over a tenth of an astronomical unit (the average distance between Earth and the sun)—a distance that is about a third of the radius of Mercury's orbit around the sun. The fact that M-dwarf systems vastly outnumber other kinds of systems carries a profound implication, according to Johnson, which is that our solar system is extremely rare. 

The implications of a galaxy chock full of planets are far-reaching, the researchers say. "It's really fundamental from an origins standpoint," says Swift, who notes that because M dwarfs shine mainly in infrared light, the stars are invisible to the naked eye. "Kepler has enabled us to look up at the sky and know that there are more planets out there than stars we can see."

Via: "California Institute Of Technology"