4 ms·

This all seems dependent on the planet being tidally locked. How do they know that? Does a certain distance from the sun absolutely guarantee it?

• robryan 16y ago
  Certain tidal force being exerted I think, it would be a combination of distance and the mass of the star.
  • zeteo 16y ago
    That doesn't say much. How can you know for sure that such a planet will be tidally locked? At low orbital radii, you even get relativistic effects: http://en.wikipedia.org/wiki/Tests_of_general_relativity#Perihelion_precession_of_Mercury http://en.wikipedia.org/wiki/Tests_of_general_relativity#Per...
• rflrob 16y ago
  From the paper on arXiv.org: "planets that show significant eccentricities – possibly like GL 581 d – are unlikely to become locked in a 1:1-resonance. Therefore, GL 581 d is not considered to rotate synchronously in this study." I'm actually disappointed in the reporter here... that took me all of 30 seconds to find in the original paper. --see edit Following up on some of the references, it does seem like the long-standing belief is that being a certain distance from the parent star strongly predisposes a planet to tidal locking: "planets close enough to their parent star to possess liquid water on their surfaces (the conventional HZ, below) should be tidally locked (Dole, 1964)," (Scalo et al, 2007); "For stellar masses below 0.6 MSun, exoplanets orbiting in the HZ become tidally locked within the first billion years (e.g., Kasting et al., 1993; Grießmeier et al., 2004, 2005)." (Lammer et al, 2007). EDIT: D'oh! The OP is talking about 581 g, not d. Serves me right to just grab the first article I see on arXiv about a planet in the Gliese 581 system.
• hugh3 16y ago
  Check out the equation towards the bottom of http://en.wikipedia.org/wiki/Tidal_locking http://en.wikipedia.org/wiki/Tidal_locking which gives a timescale for how long it takes for a body to become tidally locked to the body it orbits. I haven't plugged in the numbers for this planet, but I'm gonna assume it winds up being much shorter than the age of the star.
  • zeteo 16y ago
    Well, the link you're giving says (at the bottom) "Gliese 581 g may be tidally locked to its parent star Gliese 581" So it's not known for certain.
• hugh3 16y ago
  Check out the equation towards the bottom of http://en.wikipedia.org/wiki/Tidal_locking http://en.wikipedia.org/wiki/Tidal_locking which gives a timescale for how long it takes for a body to become tidally locked to the body it orbits. I haven't plugged in the numbers for this planet, but I'm gonna assume it winds up being much shorter than the age of the star.