YOLA 07A: A New Planet Is Discovered - p2

orbit
Gliese 581g is part of a string of planets in the Gliese 581 solar system. Two of Gliese 581g's siblings - Gliese 581e and Gliese 581b - orbit too close to their parent star to support any kind of life on them.

infrastructure
Gliese 581c skims the near side of the habitable zone, but scientists suggest that it does not have enough of a toehold in this zone to provide a stable infrastructure for organic formations.

zone
Roughly the same goes for Gliese 581d, which has a stronger presence in the habitable zone on its far side, but may not be hot enough for liquid water - opinion is not 'completely settled' on this matter.

prospect
Professor James Kasting suggests that Gliese 581g is 'smack dab in the middle' of the zone which, along with its size and composition, makes it the most exciting and realistic prospect for extra-terrestrial life yet.

overstated
The comparisons between the Earth and Gliese 581g should not be overstated, however. Even if Gliese 581g can sustain organisms, it would be a very different place to live.

gravitational pulls
Because Gliese 581 is only 1% as bright as the Sun, it exudes little warmth, and its habitable zone lies much closer. At this distance, planets get locked into strong gravitational pulls that tend to slow their rotation.

permanent
Planets become stuck with one side always facing the star, just like the Moon and the Earth. Because of this, it is likely that Gliese 581g has permanent daytime on the side facing the star and permanent shadow on the other.

estimate
Astronomers estimate that average temperatures on Gliese 581g's star side would be about 71°C and average temperatures on the other much chillier: -34°C.

horizon
Steven Vogt suggests that Gliese 581g probably has a comfortable area along the midpoint, called the terminator. Any life here would always see the star sitting on the horizon and thus experience eternal sunrise or sunset.