Our Galaxy Has at Least 100 Billion Planets, Study Shows

[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?

[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...

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.

[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.

[celoyd]

We don’t really know how many 1,500 is, because we’re missing a lot of the variables we need to have even an order-of-magnitude estimate of how common intelligent life is. It could be practically inevitable on planets with liquid water; it could be one in a million even given “animal” life. Qualified experts disagree.

And 50 light years is a long distance to travel even at a tremendous speed like 0.01c, but it isn’t that long to send postcards. If we’d sent out a bunch of reasonably good questions in 1912, we would still be interested in the answers today. (More interesting, I think, is what they would ask us.)

In retrospect, I’m assuming we’re taking a finding-intelligent-life perspective here. But if you’re thinking in terms of human expansion – terraforming and so on – then I agree.

[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.

[michaelfeathers]

I'm just troubled by the fact that alien TV signals appear to look like static.

[michaelcampbell]

> 50 light-years is a really long distance.

Compared to what we can wrap our brains around generally, sure, but in the scheme of the universe, not so much.

[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.

[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.

[bitops]

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

[arethuza]

http://www.youtube.com/watch?v=buqtdpuZxvk

[huxley]

The "Galaxy Song" only specifies that there are a 100 billion stars :-)

For some serious geeky pedantry, it's hard to beat the Wikipedia entry for the song (especially the section entitled "Accuracy of figures quoted in the lyrics"):

http://en.wikipedia.org/wiki/Galaxy_Song#Accuracy_of_figures...

[brudgers]

...and also that there is an infinity of worlds

Giordano Bruno beat him to the punch by four centuries (if of course one accepts 100,000,000,000 as a reasonable approximation of infinity).

http://www.positiveatheism.org/hist/brunoiuw0.htm#IUWTOC

[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...

[cvg]

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

[karamazov]

very appropriate 2001 reference.

[shaggyfrog]

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

[rbanffy]

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

[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.

[ifearthenight]

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