Anons concerns contd  On the gravlocked red dwarf planet  Note that a planet gravitationally locked to its star will have tidal heating like Io so its not as if everything will freeze on the night side The great advantage of a gravlocked planet is its stability I think its fair to say that stability is easier for life to deal with than instability If you look at the stability of Jupiters great red spot  years and posited to be permanent weather on a gravlocked planet should be relatively stable I presume a convection rising at the sun pole and falling at the dark pole with terrain eddies of course Such a planet will have no axial tilt no daynight cycleI dont even think it can have an eccentric orbit but Im unsure This greatly reduces the complexity of an organisms job for example a plant doesnt need the night mode earth plants need they would not have to drop leaves for winter These seem like advantages to me  Based on the best information I can find on the US Dept of Energy site solar information what plants get on a clear equinox day is about  kWHm peaking at  kWm The vast majority of that power comes in the middle  hours less than  kWHm is in morning and evening The night is essentially  kWHmnot absolutely no but to the  digit accuracy I was using yes Compare visual magnitudes of sun vs moon This varies by latitude and season of course Now lets plug this into the supposedly horrible  variation of a red dwarf Instead of roughly  time at  kW yes it really is close to that equivalent energy would be all the time at  kW Thus the variation would be  kW during minimums  of  kW and of course  is  kW Thus ignoring frequency the red dwarf plant has an easier time The lower power of red dwarfs just pull the HZ in Considering Earth shade plants which live on far less than  kWm the HZ is where the total solar and gravitational energy are right for water  Organizationally perhaps the best thing would be to treat Earthlike planets in the main flow of the article then discuss tidallylocked red dwarf planets with a note that thinking on the issue is in flux and note that chemosynthsis biospheres would be possible even around brown dwarfs or outlying moons like Titan and Europa Perhaps keeping original numbers   Suitable star systems    Spectral class   Binary systems since all but the closest binaries are ok put it here   A stable habitable zone   Planetary characteristics    Mass   Acceptable energy variation as I hope I showed about low isnt really necessary include the case of Jovian moons in the HZ   High metallicity it comes from system formation but its a planet property   Geochemistry maybe combine with metallicity   Alternative biologies   Red dwarf systems tidally locked low light  NEW Chemosynthesisbased biology   on no changes  I should add this is a really good article Maybe Im trying to gild the lily   Mistake   I am not a specialist but Mars by contrast is nearly or perhaps totally geologically dead and has lost much of its atmosphere  mass paragraph seems doubtful to me I mean Mars still has volcanoes Mount Olympus for example so it sees strange to me that its geologically dead but once again I am no specialist    Mars does have volcanoes but as far as I know theyre not really active so nothing is really powering them and geological activity isnt really showing up    Luna Earths Moon has volcanoes and its accepted as geologically dead The presence of volcanoes doesnt mean ACTIVE volcanoes  Thats basically what I was trying to say I guess I just never made it really clear     Picture Size  Can a larger size by found for the Habitability Zone picture Id like to use it as a background but it wont scale up   I downloaded it here  httplibrarythinkquestorg though I cant remember the exact spot on the site An image search for habitable zone turns it up first thing but only at k    Earths geological activity I am pretty sure that the earth isnt geologically active simply because of its large masssurface area ratio From what I have read I believe that planets are probably heated mostly by radioactive decay andor tidal for