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Milky Way may have billions of Earth-like planets, scientists say

By Seth Borenstein

AP Science Writer

LAST UPDATED: 03:42 p.m. HST, Nov 04, 2013

WASHINGTON >> Space is vast, but it may not be so lonely after all: A study finds the Milky Way is teeming with billions of planets that are about the size of Earth, orbit stars just like our sun, and exist in the Goldilocks zone -- not too hot and not too cold for life.

Astronomers using NASA data have calculated for the first time that in our galaxy alone, there are at least 8.8 billion stars with Earth-size planets in the habitable temperature zone.

The study was published Monday in the journal Proceedings of the National Academy of Science.

For perspective, that's more Earth-like planets than there are people on Earth.

As for what it says about the odds that there is life somewhere out there, it means "just in our Milky Way galaxy alone, that's 8.8 billion throws of the biological dice," said Geoff Marcy, from the University of California at Berkeley, who co-authored the study with Andrew Howard of the University of Hawaii.

The next step, scientists say, is to use powerful space telescopes that have yet to be launched to look for atmospheres on these planets. That would yield further clues to whether any of these planets do, in fact, harbor life.

The findings also raise a blaring question, Marcy said: If we aren't alone, why is "there a deafening silence in our Milky Way galaxy from advanced civilizations?"

In the Milky Way, about 1 in 5 stars that are like our sun in size, color and age have planets that are roughly Earth's size and are in the habitable zone where life-crucial water can be liquid, according to intricate calculations based on four years of observations from NASA's now-crippled Kepler telescope.

If people on Earth could only travel in deep space, "you'd probably see a lot of traffic jams," Bill Borucki, NASA's chief Kepler scientist, joked today.

The Kepler telescope peered at 42,000 stars, examining just a tiny slice of our galaxy to see how many planets like Earth are out there. Scientists then extrapolated that figure to the rest of the galaxy, which has hundreds of billions of stars. 

For the first time, scientists calculated -- not estimated -- what percent of stars that are just like our sun have planets similar to Earth: 22 percent, with a margin of error of plus or minus 8 percentage points.

Kepler scientist Natalie Batalha said there is still more data to pore over before this can be considered a final figure.

There are about 200 billion stars in our galaxy, with 40 billion of them like our sun, Marcy said. One of his co-authors put the number of sun-like stars closer to 50 billion, meaning there would be at least 11 billion planets like ours.

Based on the 1-in-5 estimate, the closest Earth-size planet that is in the habitable temperature zone and circles a sun-like star is probably within 70 trillion miles of Earth, Marcy said.

And the 8.8 billion Earth-size planets figure is only a start. That's because scientists were looking only at sun-like stars, which are not the most common stars. 

An earlier study found that 15 percent of the more common red dwarf stars have Earth-size planets that are close-in enough to be in the not-too-hot, not-too-cold Goldilocks Zone.

Put those together and that's probably 40 billion right-size, right-place planets, Marcy said. 

And that's just our galaxy. There are billions of other galaxies. 

Scientists at a Kepler science conference today said they have found 833 new candidate planets with the space telescope, bringing the total of planets they've spotted to 3,538, but most aren't candidates for life.

Kepler has identified only 10 planets that are about Earth's size circling sun-like stars and are in the habitable zone, including one called Kepler 69-c.

Because there are probably hundreds of planets missed for every one found, the study did intricate extrapolations to come up with the 22 percent figure -- a calculation that outside scientists say is fair. 

"Everything they've done looks legitimate," said MIT astronomer Sara Seager.


For more information, the journal PNAS: http://www.pnas.org 

NASA's Kepler Telescope: http://1.usa.gov/171Tx8X

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PMINZ wrote:
Please stop the insanity on paying Billions of Tax money on finding other planets in the galaxy and pay attention to fixing this Planet!
on November 4,2013 | 02:33PM
Maneki_Neko wrote:
Guess what... the rest of them all voted in favor of same sex marriage.
on November 4,2013 | 04:48PM
gtracer66 wrote:
Really? Do we need to bring politics and gay marriage into EVERY news item? Just as there may be other planets with life out there, there are other problems that we face here that need to be addressed as well.
on November 5,2013 | 03:54AM
rayhawaii wrote:
I could of told you that for free. Well maybe for a diet coke?
on November 4,2013 | 05:28PM
syhud wrote:
That's not what they taught me in bible school.
on November 4,2013 | 05:45PM
gtracer66 wrote:
The Bible, while a great source of guidance, is not the only story ever told. All civilizations have/had stories similar to the Bible even though most never heard of each other. Besides, the writers of the Bible didn't have telescopes or even a concept of space and the physical universe as we know it today. Unless you believe and include Ancient Aliens theories as the source of events in the Bible. Which of course explains why so many other groups created their own version of the same stories as found in the Bible.
on November 5,2013 | 04:00AM
Nevadan wrote:
Fascinating. But is it surprising? No. It is much more exciting if these astronomers, or astrophysicists, address the dynamics of the universe. The theory can start with the Chandrasekhar Limit, and base it on the General Theory of Relativity, instead of the Special Theory of Relativity. Experimentally start with the Milky Way. NASA has the expertise. The religious folks would be interested too. It would shed light on whether there is a Supreme Being.
on November 4,2013 | 06:42PM
Bothrops wrote:
We are going to need a few Earth-like planets to move to if we keep trashing this one.
on November 4,2013 | 08:07PM
brusselsprouts wrote:
I agree - survival of the human species not to mention natural phenomena that earth or our solar system could unleash that would threaten our existence. i mean if Iceland and the Yellowstone Caldera go off at the same time eeek. So find those class M planets and create the warp drive. Proton torpedoes and Cloaking device would be nice too. But in the mean time Love Your Earth.
on November 4,2013 | 10:09PM
gtracer66 wrote:
If Iceland and/or Yellowstone go off, we can all just bend over and kiss our butts goodbye. And Yellowstone is getting near the time estimated for eruptions.
on November 5,2013 | 04:03AM
brusselsprouts wrote:
nanu nanu
on November 4,2013 | 09:59PM
ColinKona wrote:
Geez, 8.8 billion; that's almost as many as the channels on cable TV! Seriously, to answer the question, "If there's really so much intelligent life out there, why aren't they communicating with us?" Kinda like parents trying to talk to self-obsessed teenagers, isn't it? I suspect the Universe has just put Earth in "time out" until we cool our jets, so to speak. Tough love. Beats being vaporized or eaten, no?
on November 5,2013 | 05:23AM
Kalaheo1 wrote:
One reason they're not communicating with us is they are really, really a long way away. Radio broadcasts take thousands of years to cross the open space between us and those plants.
on November 5,2013 | 06:51AM
palani wrote:
As for what it says about the odds that there is life somewhere out there, it means "just in our Milky Way galaxy alone, that's 8.8 billion throws of the biological dice," ...

These big thinkers are thinking too small. The universe is infinite. That means there are an unlimited number of not just planets, but stars, solar systems, and entire galaxies as well. The probability of life beyond our world is therefore a certainty.

on November 5,2013 | 05:27AM
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