Just-right planet that can support life detected | Reuters

gliese 581 is a tricky system.  it’s a red dwarf star, only one third the mass of our own sun.  five of the six planets discovered so far are so close in that their orbital years range from three to 67 earth days.  most of them are presumed to be tidally locked due to their proximity to the star, which complicates habitability because half the planet is always sunny and half is always dark.

planet 581c, the first one to hit the poorly researched science news circuit back in 2007, was mistakenly reported as having liquid water and vast oceans and earth-like temperatures, when in reality it likely has a massive venus-like atmosphere complete with runaway greenhouse effect, and surface temperatures that would boil oceans, if there is any water, which hasn’t been confirmed.

581g is the sixth planet found so far, and the first of six to lie smack in the middle of the habitable zone, where temperatures could be earthlike, and given the presence of water and atmosphere, could sustain life.

how much life is the question, of course.  no sunlight on the dark side means no plant life as we know it, regardless of temperature.  which limits us to the light side, and gives us two main scenarios depending on whether the atmosphere can radiate excess heat from the light side around to the dark side, cooling one hemisphere and warming the other.

if yes, then we could have an entire hemisphere, on a planet with four times earth’s mass and likely several times earth’s surface area, of eternal sunshine ranging from tropical climates in the center to arctic summer along the edges.

if not, you’d have a scorching desert and a frozen one sandwiching a narrow band of temperate zone all along the shadow line.  half of this band would receive sunlight without end, but from very low in the sky.  and likely most of the habitable zone would be open water.