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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 planet

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 15y ago
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/nature10684.html 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.
- Retric 15y ago
  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 15y ago
    The paper can be found here: http://www.eso.org/public/archives/releases/sciencepapers/eso1204/eso1204.pdf http://www.eso.org/public/archives/releases/sciencepapers/es...

mturmon 15y ago

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/nature10684.html 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.

Retric 15y ago
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 15y ago
  The paper can be found here: http://www.eso.org/public/archives/releases/sciencepapers/eso1204/eso1204.pdf http://www.eso.org/public/archives/releases/sciencepapers/es...