  If life is sustained by a process of photosynthesis, not necessarily the same
existing on Earth, the surface temperature of the star and the orbit of the
host planet cannot be whatsoever. In fact the global life cycle, no matter how
complicated, must contain in general an upper photochemical branch and a lower
dark branch, characterized by a higher and a lower temperature. These two
temperatures are star-orbit related. The velocity along the cycle or, in other
words, the power of the life machine, depends in general on several other
parameters. First of all the Gibbs photon availability, which is a star-orbit
parameter and is the input for the upper branch. Then follows the energy
cascade that develops along the organic web with a large number of interactions
and typical times that must match the typical times generated by the
combination of spin value and orientation, eccentricity and precession.
Finally, the capacity of the web to keep the global life cycle running along
the life span of the star, comes from some inner form of self-endurance and
self-balance. The property of not being transient could be the right way of
introducing the concept of intelligent life.
