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World Builders™
World Builders™
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Session One -- Astronomy
Session One -- Astronomy
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The Life Zone
The Life
Zone
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The
"Goldilocks Model"
Is Your World Too
Hot, Too Cold or Just Right for Life?
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So
far as we know, life
needs a liquid of some
kind in order to work
chemically. The life
forms that we are
familiar with are
dependent on water. Water is made
of small,
plentiful atoms and
water, often in the
form of ice, is
abundant in the
universe.
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Perhaps there are life forms
that use other liquids, such as liquid methane, but we don't
know about them. We tend to think in terms of water-based
life.
It seems reasonable to believe that planets
that are close to the sun are too hot to have liquid water on
their surfaces. Planets that are far away would probably be too
cold. There is a region in the middle where planets might have
temperatures that would permit liquid water to exist on their
surfaces. The space in which these planets could orbit is called
the life zone, or zone of habitability.
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However,
a planet in the life zone might not be suitable for life due
to other variables. For instance, if there is a dense atmosphere
and a strong greenhouse effect, as there is on Venus, temperatures
at the surface could be very hot and not suitable for life as
we know it. This diagram shows a planet that has a strong Greenhouse
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If the planet is too small to hold an atmosphere,
it will not have water on the surface no matter how comfortable
the temperatures are. Water would evaporate, and the gas molecules
would just wander away.
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Planets far from their sun, like
Saturn in our solar system, receive little heat from the sun
and are thought to be made mainly of frozen gases. However, local
conditions might generate some heat.
Gravity can exert forces that
cause friction in rocks and ice. The friction can generate heat
even on dark planets.
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Go on to
Gravity
Can Cause Stresses that Generate Heat for more information.
More technical help with calculating the
habitable zone for your star can be found at
http://www.ess.sunysb.edu/fwalter/AST101/habzone.html
©
1998, 2003 Elizabeth Anne Viau.
All rights reserved. This material may be used by individuals
for instructional purposes but not sold. Please inform the author
if you use it at eviau@earthlink.net
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