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."
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:
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.
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.
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?