# Does every star have planets?

#### rod

Helio developed this thread showing some more details on exoplanets using Excel, https://forums.space.com/threads/exoplanet-summary.53323/#post-562890

Concerning the two exoplanet sites used in this thread, I found 3633 individual stars with exoplanets reported at the .eu site and 3659 individual stars reported for the nasa archive site. How many stars were studied that came up empty and surveyed before less than 4,000 stars can be shown with exoplanets, I do not know.

So my observation here. There are billions of stars in the MW, yet today we know < 3700 have exoplanets. The article title stated, "Does every star have planets?" My answer is no and the article is a easy to read and understand too.

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Helio

#### Helio

How many stars were studied that came up empty and surveyed before less than 4,000 stars can be shown with exoplanets, I do not know.
The Kepler mission using the transit method , IIRC, attempted to survey 150,000 stars.

The probability of finding a transit is simply D/2a. Where "D" is the diameter of the star and "a" is the semi-major axis.

For the Earth-Sun, the probability is just under 0.5%. For M-type stars with close-orbiting planets, I think it can be as high as 20%. [That would make for an interesting graph. ]

The no. of exoplanets by discovery method was easy to add to the program:

[Note: updated to give percentages and today's list of exoplanets.]

So my observation here. There are billions of stars in the MW, yet today we know < 3700 have exoplanets. The article title stated, "Does every star have planets?" My answer is no and the article is a easy to read and understand too.
The article did mention that the no. of exoplanets is about equal to the no. of stars. This isn't something new, but a lot more data is needed to tweak this estimate.

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#### Helio

In playing around the exo files, I found this old crystal ball look (2011) that I projected for growth in the number for exoplanet discoveries. Had I stayed with the actual values I would have been just about right-on-the-mark.

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