Astronomy Picture of the Day [1]Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2020 January 31 [2]See Explanation. Clicking on the picture will download the highest resolution version available. Goldilocks Zones and Stars Infographic Credit: [3]NASA [4]ESA, Z. Levy ([5]STScI) Explanation: [6]The Goldilocks zone is the habitable zone around a star where it's not too hot and not too cold for liquid water to exist on the surface of orbiting planets. [7]This intriguing infographic includes relative sizes of those zones for yellow G stars like the Sun, along with orange K dwarf stars and red M dwarf stars, both cooler and fainter than the Sun. [8]M stars (top) have small, close-in Goldilocks zones. They are also seen to live long (100 billion years or so) and are very abundant, making up about 73 percent of the stars in the Milky Way. Still, they have very active magnetic fields and may produce too much radiation harmful to life, with an estimated X-ray irradiance 400 times the quiet Sun. Sun-like G stars (bottom) have large Goldilocks zones and are relatively calm, with low amounts of harmful radiation. But they only account for 6 percent of Milky Way stars and are much shorter lived. In the search for habitable planets, [9]K dwarf stars could be just right, though. [10]Not too rare they have 40 billion year lifetimes, much longer than the Sun. With a relatively wide habitable zone they produce only modest amounts of harmful radiation. [11]These Goldilocks stars account for about 13 percent of the stars of the Milky Way. Tomorrow's picture: Apollo 14 Earthrise __________________________________________________________________ [12]< | [13]Archive | [14]Submissions | [15]Index | [16]Search | [17]Calendar | [18]RSS | [19]Education | [20]About APOD | [21]Discuss | [22]> __________________________________________________________________ Authors & editors: [23]Robert Nemiroff ([24]MTU) & [25]Jerry Bonnell ([26]UMCP) NASA Official: Phillip Newman [27]Specific rights apply. [28]NASA Web Privacy Policy and Important Notices A service of: [29]ASD at [30]NASA / [31]GSFC & [32]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2001/STSCI-H-p2006a-h-8333x5000.jpg 3. https://hubblesite.org/ 4. https://www.spacetelescope.org/ 5. https://stsci.edu/ 6. https://apod.nasa.gov/apod/ap140307.html 7. https://hubblesite.org/contents/news-releases/2020/news-2020-06 8. https://arxiv.org/abs/1707.07007 9. https://www.nasa.gov/feature/goddard/2019/k-star-advantage 10. https://en.wikipedia.org/wiki/Kepler-442b 11. https://arxiv.org/abs/1606.09580 12. https://apod.nasa.gov/apod/ap200130.html 13. https://apod.nasa.gov/apod/archivepix.html 14. https://apod.nasa.gov/apod/lib/apsubmit2015.html 15. https://apod.nasa.gov/apod/lib/aptree.html 16. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 17. https://apod.nasa.gov/apod/calendar/allyears.html 18. https://apod.nasa.gov/apod.rss 19. https://apod.nasa.gov/apod/lib/edlinks.html 20. https://apod.nasa.gov/apod/lib/about_apod.html 21. http://asterisk.apod.com/discuss_apod.php?date=200131 22. https://apod.nasa.gov/apod/ap200201.html 23. http://www.phy.mtu.edu/faculty/Nemiroff.html 24. http://www.phy.mtu.edu/ 25. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 26. http://www.astro.umd.edu/ 27. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 28. https://www.nasa.gov/about/highlights/HP_Privacy.html 29. https://astrophysics.gsfc.nasa.gov/ 30. https://www.nasa.gov/ 31. https://www.nasa.gov/centers/goddard/ 32. http://www.mtu.edu/