01:750:109 Chapter Notes - Chapter 15.2: Interstellar Travel, Horsepower, Drake Equation
The Search for Life Among the Stars
●Large telescopes could in principle detect the presence of surface life on extrasolar planets, but
no foreseeable technology could detect life that is hidden deep underground in other solar
systems
●Therefore, will focus on the search for life on planets w habitable surfaces-- surfaces w temps
and pressures that could allow liquid water to exist
How can we identify potentially habitable planets?
Four Factors in Surface Habitability
●Planet must orbit at a distance that places it within the star's habitable zone
, meaning the range
of distances from the star in which a planet may be cool enough to allow water vapor to
condense as rain and make oceans, but no so cold that all the water freezes
●Planet should have sources of gas to make an atmosphere and to condense into oceans
○On Earth, this gas came from volcanic outgassing
●Planet needs a climate that remains at least moderately stable over long time periods
○On Earth, this stability comes from the carbon dioxide cycle, which depends on plate
tectonics
●Planet's atmosphere should be protected from its star's stellar wind
○On Earth, this protection comes from the planetary magnetic field, which arises from
the combination of Earth's rotation speed and the interior core layer of convecting,
molten metal
Signatures of Life
●Observing surfaces of potentially habitable worlds will require far more powerful telescopes
than we have today but we might still learn whether such worlds harbor life through
spectroscopy that may be possible w telescopes not too much more advanced than today's
Is there intelligent life beyond Earth?
Document Summary
Large telescopes could in principle detect the presence of surface life on extrasolar planets, but no foreseeable technology could detect life that is hidden deep underground in other solar systems. Therefore, will focus on the search for life on planets w habitable surfaces-- surfaces w temps and pressures that could allow liquid water to exist. Planet should have sources of gas to make an atmosphere and to condense into oceans. On earth, this gas came from volcanic outgassing. Planet needs a climate that remains at least moderately stable over long time periods. On earth, this stability comes from the carbon dioxide cycle, which depends on plate tectonics. Planet"s atmosphere should be protected from its star"s stellar wind. On earth, this protection comes from the planetary magnetic field, which arises from the combination of earth"s rotation speed and the interior core layer of convecting, molten metal. The search for signals from other civilizations known as the search for extraterrestrial intelligence (seti)
