Probabilities in the Galaxy

The search for exoplanets is currently being carried out by the Kepler satellite telescope. Kepler is a NASA space telescope. [3] It was launched on March 7, 2009 to search for extrasolar planets,[1]. [4] Erik Petigura from the University of California at Berkeley evaluated exactly 150,000 stars in 2013. The Kepler telescope identified 42,000 of the 150,000 stars observed that resemble our sun, i.e. stars of spectral class G. Kepler" has discovered a total of 603 systems with planets in their orbits. 10 planets are about the size of the earth and orbit their star in the so-called habitable zone,[5] where life-friendly temperatures prevail. [6]

To evaluate the Kepler data, fluctuations in the brightness of stars that indicate a transit of a planet in front of its sun are used. Due to the different orbital inclinations of the planets against our line of sight, however, only a part of earth-like planets are covered that can be observed from our direction. The geometric probability F_K of such a transit for the earth is 0.47 % = 1/213 %. [2] [7]

So there could be a maximum of 213 times as many systems with planets. With 603 systems discovered, this results in 128,439 undiscovered planetary systems. That is 85.6 % of the observed stars. This means that a maximum of 85.6% of all solar systems in the galaxy could have planets.

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