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Beyond Earthly Skies

Occurrence of Terrestrial Planets around Cool Stars

12 Aug 2014, 22:00 UTC
Occurrence of Terrestrial Planets around Cool Stars
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The ever growing number of detected exoplanets shows that small planets are far more common than larger ones. A study by Morton & Swift (2014) examines the abundance of terrestrial planets with orbital periods less than 150 days around cool stars with effective temperatures below 4,000 K (i.e. red dwarf stars). These stars make up the majority of stars in the galaxy. For comparison, the Sun has an effective temperature of 5,778 K. The study analysed data from NASA’s Kepler space telescope on exoplanets in the size range between 0.5 to 4.0 Earth radii.Figure 1: Artist’s impression of a terrestrial planet around a cool red dwarf star.Figure 2: Distribution of planets orbiting cool stars with orbital periods less than 150 days. The blue horizontal lines represent the standard “occurrence rate per bin” calculations. The vertical red lines represent the number of planets with a particular radius is observed. Morton & Swift (2014).Results from the study indicate there is an average of 2.00 ± 0.45 planets between 0.5 to 4.0 Earth radii per cool star. Additionally, for planets between 0.5 to 1.5 Earth radii, there is an average of one planet per cool star. The distribution of exoplanets shows a rise ...

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