Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Mike G on 19/04/2014 10:23:01

Title: How can Kepler-186f be in the habitable zone?
Post by: Mike G on 19/04/2014 10:23:01

According to phys.org It's at about 4AU or roughly Jupiter orbit, and the star is an M1 red dwarf which according to wiki is at about 3.5% luminousity.  How can the habitable zone extend out so far from the star?

http://en.wikipedia.org/wiki/M_dwarf#Description_and_characteristics
http://phys.org/news/2014-04-potentially-habitable-earth-sized-planet-liquid.html#ajTabs

Title: Re: How can Kepler-186f be in the habitable zone?
Post by: evan_au on 19/04/2014 13:09:45

The way I read the article at phys.org is:

• The diagram comparing our Solar system and the Kepler-186 star system is drawn approximately to scale.
  
• Kepler 186-f orbits its star in 130 Earth days, at approximately the radius of Venus.
  
• Kepler 186 is a dwarf star, and Kepler 186-f receives less heat from its star than does the Earth, placing it at the outer edge of the "habitable zone" with liquid water
  
• The purpose of using the large Earth-based telescopes was to better image the system, and exclude other possible explanations such as a binary star system, where another dimmer star, at (say) the radius of Neptune could cause periodic dips in the light from Kepler 186, leading to a false impression of an orbiting planet.
  
• With speckle interferometry, they were able to image as close as the radius of Jupiter's orbit (an impressively high resolution), and exclude some of these possible alternative explanations for the light dips observed by the Kepler telescope.
  
• I presume that some of these explanations might also be excluded by measuring the Doppler shift of the star to high resolution - but this can be difficult if the star is a dim dwarf.