

Our Galaxy Has at Least 100 Billion Planets, Study Shows - jfoucher
http://www.jpl.nasa.gov/news/news.cfm?release=2012-010

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pessimist
Hmm, "Our Milky Way galaxy contains a minimum of 100 billion planets according
to a detailed statistical study based on the detection of three extrasolar
planets by an observational technique called microlensing."

So we looked in 3 places, found 3 planets and are extrapolating to 100
billion? Surely I would wait for a few more examples?

Edit: Reading the full story, "Of the approximately 40 microlensing events
closely monitored, three showed evidence for exoplanets. Using a statistical
analysis, the team found that one in six stars hosts a Jupiter-mass planet.
What's more, half of the stars have Neptune-mass planets, and two-thirds of
the stars have Earth-mass planets. Therefore, low-mass planets are more
abundant than their massive counterparts."

I dont get it. Any explanation?

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mturmon
The reason it's OK to extrapolate in this way would appear to be in this fact
(from TFA):

"Unlike other prominent planet-detection techniques, which measure the shadows
of planets passing in front of their stars (transit) or measure the wobble of
a star due to the gravitational tug of a planet (radial velocity and
astrometry), the gravitational-lensing technique is unbiased in the selection
of the host star."

To know more, we have to read the story in _Nature_ , which is here:

[http://www.nature.com/nature/journal/v481/n7380/full/nature1...](http://www.nature.com/nature/journal/v481/n7380/full/nature10684.html)

Look at the error bars on their percentages. Super-earths (planets of 5-10x
earth mass) are present on "62 +35 -37"% of systems. So, your intuition that
the extrapolation was shaky is correct.

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Retric
Assuming the title and your numbers are correct they basically said. 'We
estimate that there is a 95% chance that there are 250Billion stars +/- 60%
which means there is a 97.5% chance that there are at least 100billion
planets.'

However, the actual study costs US$32 so I am not buying it so somewhere in
the game of telephone that we just played information could have mutated.

~~~
mchouza
The paper can be found here:

[http://www.eso.org/public/archives/releases/sciencepapers/es...](http://www.eso.org/public/archives/releases/sciencepapers/eso1204/eso1204.pdf)

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JeffL
Sounds a little more lonely when you read "it's likely there are a minimum of
1,500 planets within just 50 light-years of Earth." 1,500 isn't that many, and
50 light-years is a really long distance.

~~~
felipemnoa
We are pretty isolated. Had we belonged to a cluster of stars our chances of
finding life would have been greater.

From Wikipedia: <http://en.wikipedia.org/wiki/Star_cluster>

Globular clusters, or GC, are roughly spherical groupings of from 10,000 to
several million stars packed into regions of from 10 to 30 light years across.

~~~
martey
From <http://en.wikipedia.org/wiki/Globular_cluster> :

"However, they are not thought to be favorable locations for the survival of
planetary systems. Planetary orbits are dynamically unstable within the cores
of dense clusters because of the perturbations of passing stars."

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julian37
This is very exciting.

On a related note, the number put forth by the study (at least one planet per
star, on average) is roughly consistent with Drake's 1961 estimate that half
of all stars will have planets, and stars with planets will have 2 planets
capable of developing life.

Except, of course, that Drake estimated an average of >=1 _habitable_ planets
per star. Still, it's good to see one of his estimates being corroborated.

<http://en.wikipedia.org/wiki/Drake_equation>

~~~
microarchitect
Drake just pulled a bunch of numbers out of a hat and multiplied them. This is
a much more serious scholarly effort.

~~~
demallien
Drake did no such thing. The Drake equation was not designed to give us an
answer as to the number of civilisations out there, but to show us which
questions needed to be answered to help us identify candidate search
locations.

As an example, the Kepler mission is a direct result of the Drake equation,
designed to resolve the first two parameters - fp and ne.

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johnnyg
Now all we need to do is get each of them to send us $150. US debt crisis
solved.

~~~
eru
Where should they take the money from? You print all the dollars. Unless
there's been trade with aliens, they won't have any earthling money.

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bitops
Eric Idle already told us that quite a long time ago.

~~~
arethuza
<http://www.youtube.com/watch?v=buqtdpuZxvk>

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Joakal
I believe there are much more planets because not every planet has a star:
[http://www.dailygalaxy.com/my_weblog/2011/09/billions-of-
dar...](http://www.dailygalaxy.com/my_weblog/2011/09/billions-of-dark-planets-
roam-the-milky-way.html)

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cvg
that's about one for every person that's ever lived.

~~~
karamazov
very appropriate 2001 reference.

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shaggyfrog
The headline reads even better if you imagine Carl Sagan saying " _billion_ ".

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rbanffy
So, where are the other kids? We want to play.

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rokhayakebe
I cannot even start to grasp the meaning of 100B planets.

I read that if the "Milky Way" was the size of China, then the the sun and 6
closest planets around together would be the size of one quarter.

~~~
InclinedPlane
I just did the math on that, it's about right. It's closer to a dime though.

~~~
thret
If you really did the math, I love you.

~~~
InclinedPlane
It's straightforward math, the hardest part is coming up with a width for
China (I ended up using an approximation of 5,000 km), all of the other
figures are on wikipedia (radius of Saturn's orbit, size of the milky way).
Also, if you want to be super lazy you can get google to convert units for
you:

[https://www.google.com/search?ie=UTF-8&q=2.87+billion+km...](https://www.google.com/search?ie=UTF-8&q=2.87+billion+km+%2F+100%2C000+ly+*+5%2C000+km#sclient=psy-
ab&hl=en&source=hp&q=2.87+billion+km+%2F+100%2C000+light+years+*+5%2C000+km&pbx=1&oq=2.87+billion+km+%2F+100%2C000+light+years+*+5%2C000+km&aq=f&aqi=&aql=&gs_sm=e)

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ifearthenight
Now I feel a bit of a loser for only having visited one so far.

