Lecture #38: Extrasolar Planets
More on the Habitable zone
-- graphic here
The habitable zone is the region in any star system, based on distance to the star, wherein we might expect
the proper temperatures for liquid water to exist on the surface of the planet.
The assumption is that surface water is the key for life.
Surface water also requires sufficient air pressure, due to the weight of the atmosphere, to keep the water
from evaporating suddenly, called boiling.
We think of boiling as needing high temperature, but that is only because we have Earth air pressure in mind--
it can happen at lower temperatures if the air pressure is lower.
So far, we have only candidates for Earth-sized planets in the habitable zone of their stars, meaning we need to
watch the candidates for a few more orbits to know if they are really what we think.
Since the demise of the Kepler satellite, we may not get the data for the candidates to graduate to full detections,
or the data may exist but is still being analyzed.