A habitable zone is the region around a star where an Earth-like
planet can maintain liquid water on its surface. The habitable
zone is the area that might potentially support life. From the
center of the earth to the far galaxies we find evidence that
life arose from cosmic processes. The iron in our blood and the
calcium in our bones were made inside stars. All silver and gold
was forged by stars that exploded long ago. The habitable zone
first included the orbits of Venus to Mars, planets close enough
to the sun for solar energy to make the chemistry of life, but
not so close as to boil off water or break down the organic
molecules on which life depends. The habitable zone may be
larger than originally considered. The strong gravitational pull
caused by large planets may produce enough energy to
sufficiently heat the cores of orbiting moons. Life has proven
itself tough here on Earth. It may be able to thrive in more
extreme environments. An imaginary spherical shell surrounding a
star throughout which the