Cosmic census finds crowd of planets in our galaxy

Feb 20, 2011 By SETH BORENSTEIN , AP Science Writer
This Aug. 6, 2010 photo shows the Milky Way above wind turbines near Lake Benton and Hendricks, Minn. Scientists have estimated the first cosmic census of planets in our galaxy and the numbers are astronomical: at least 50 billion planets in the Milky Way. At least 500 million of those planets are in the not-too-hot, not-too-cold zone where life could exist, scientists announced Saturday, Feb. 19, 2011. The numbers were extrapolated from the early results of NASA's planet-hunting Kepler telescope. (AP Photo/The Star Tribune, David Brewster) ST. PAUL PIONEER PRESS OUT; MINNEAPOLIS-AREA TV OUT; MAGS OUT

(AP) -- Scientists have estimated the first cosmic census of planets in our galaxy and the numbers are astronomical: at least 50 billion planets in the Milky Way.

At least 500 million of those are in the not-too-hot, not-too-cold zone where life could exist. The numbers were extrapolated from the early results of NASA's planet-hunting Kepler telescope.

Kepler science chief William Borucki says scientists took the number of planets they found in the first year of searching a small part of the and then made an estimate on how likely stars are to have planets. Kepler spots planets as they pass between Earth and the star it orbits.

So far Kepler has found 1,235 candidate planets, with 54 in the Goldilocks zone, where life could possibly exist. Kepler's main mission is not to examine individual worlds, but give astronomers a sense of how many planets, especially potentially habitable ones, there are likely to be in our galaxy. They would use the one-four-hundredth of the night sky that Kepler is looking at and extrapolate from there.

Borucki and colleagues figured one of two stars has planets and one of 200 stars has planets in the , announcing these ratios Saturday at the American Association for the Advancement of Science annual conference in Washington. And that's a minimum because these stars can have more than one planet and Kepler has yet to get a long enough glimpse to see planets that are further out from the star, like Earth, Borucki said.

For example, if Kepler were 1,000 light years from Earth and looking at our sun and noticed Venus passing by, there's only a one-in-eight chance that Earth would also be seen, astronomers said.

To get the estimate for the total number of planets, scientists then took the frequency observed already and applied it to the number of stars in the Milky Way.

For many years scientists figured there were 100 billion stars in the Milky Way, but last year a Yale scientist figured the number was closer to 300 billion .

Either way it shows that Carl Sagan was right when he talked of billions and billions of worlds, said retired astronomer Steve Maran, who praised the research but wasn't part of it.

And that's just our galaxy. Scientists figure there are 100 billion .

Borucki said the new calculations lead to worlds of questions about life elsewhere in the cosmos. "The next question is why haven't they visited us?"

And the answer? "I don't know," Borucki said.

Explore further: The changing laws that determine how dust affects the light that reaches us from the stars

More information: Kepler site: http://kepler.nasa.gov/

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Quantum_Conundrum
1 / 5 (3) Feb 20, 2011
Since the universe allegedly has a radius of 13.1 billion ly, then if you "over-estimate" the volume of a galaxy using the SPHERE formula, and using 60,000ly radius for galaxies, and leave plenty room in every direction, being an order of magnitude more empty space than occupied space, which is to say, an average of 1 galaxy per 9E17 cubic light years (600,000ly radius sphere), you actually find that the universe should contain about 10.4 TRILLION galaxies.

If we used Andromeda as a yardstick, then the midpoint between andromeda and milky way would be our "average radius" of space assigned to a single galaxy. This would be 1.1 million ly radius of space per galaxy.

Then even so, you would still get 1.689 TRILLION Galaxies.

Wouldn't expect a cosmologist to be able to do real math anyway.
omatumr
1 / 5 (4) Feb 20, 2011
Congratulations!

Stars circled by planets may be ordinary, not be "special."

The one here exploded 5 Gyr ago to eject all of the material now orbiting the Sun, and then reformed on the collapsed SN core:

youtube.com/watch?v=AQZe_Qk-q7M
Nik_2213
5 / 5 (2) Feb 20, 2011
Oh dear...

QC, did the star calculation distinguish between 'globular' and 'spiral' galaxies ??

Also, IIRC, O, helioseismology would reveal such a 'degenerate' core, surely ??
barakn
5 / 5 (4) Feb 20, 2011
Since the universe allegedly has a radius of 13.1 billion ly, then if you "over-estimate" the volume of a galaxy using the.. bla bla bla ...
Then even so, you would still get 1.689 TRILLION Galaxies.

Wouldn't expect a cosmologist to be able to do real math anyway.

Real math? Let's see how many stupid assumptions you made. First, you assumed the visible universe has a radius of 13.1 billion light years, based apparently on a false memory of the current consensus of the age at 13.75 billion years. However, this neglects the expansion of space. The radius of the universe is much larger than 13.75 billion light years. You also assume a constant density throughout time. Early on, the galaxies would have been closer together because expansion had yet to move them as far apart and gravity hadn't merged some together. (cont'd)
barakn
5 / 5 (3) Feb 20, 2011
You also assume a uniform distribution when in fact galaxies occur in the shape of filaments or membranes between enormous voids. To fudge your number you highballed your estimates of galaxy density - even your lower estimate is more typical of the local cluster of galaxies than of average space.

And of course there's the fact that you approached the problem backwards. The correct way of performing this calculation is to use observation, not by using made-up numbers. Simply perform a survey and count the number of galaxies in a few different direction, and then the total number comes from assuming a spherically symmetrical distribution (not a perfect assumption but far better than any of yours).
Snowboarder
5 / 5 (2) Feb 21, 2011
I believe the current estimate for the size of the visible universe is a sphere roughly 90 billion ly in diameter. Also Andromeda is moving towards us, so not really a fair measuring stick for average distance between galaxies. 3 to 5 billion years from now we'll probably collide.
d_robison
5 / 5 (1) Feb 21, 2011
You also assume a uniform distribution when in fact galaxies occur in the shape of filaments or membranes between enormous voids. To fudge your number you highballed your estimates of galaxy density - even your lower estimate is more typical of the local cluster of galaxies than of average space.

And of course there's the fact that you approached the problem backwards. The correct way of performing this calculation is to use observation, not by using made-up numbers. Simply perform a survey and count the number of galaxies in a few different direction, and then the total number comes from assuming a spherically symmetrical distribution (not a perfect assumption but far better than any of yours).


You forgot to mention that he assumes the universe is a perfect sphere, and that the edge of the visible universe is indeed the edge of our actual universe (not just that which is currently observable).
hush1
not rated yet Mar 01, 2011
It is time for birth control.
For planets.
The Universe simply does not have the resources to support this.
Unsustainable.

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