Eagle Nebula M 16 Gaseous Pillars

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Other Planetary Systems
Astronomers have learned in recent years that
planets may be commonplace around stars. Does
this mean that life also is commonplace?
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Orion Nebula (M 42) Star Formation
Protoplanetary Disks Abound
100 AU (13 light hours)
2.5 light years
The Trapezium
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Barycentric Motion Within a Two-Body System
Barycenter
Star with mass Ms
Planet with mass Mp


Rs
Rp
Rs
Mp

Rp
Ms
Note that for the Sun and Jupiter The sun is
1000 times more massive than Jupiter, thus the
sun is 1000 times close to the barycenter than is
Jupiter. So, what is the size of the suns orbit
around the Jupiter-Sun barycenter? What would the
above picture look like for Jupiter and the sun?
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Wobble of the Sun As seen from a distance of 33
light years
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Doppler Velocity Curve of HD 209458
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Detecting Planetary Transit of HD 209458
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The Exoplanet Orbiting HD 189733
This planet orbits once every 2.2 days with an
orbital plane that is nearly in our line of sight.
Thus, the planet transits the star and produces a
small decline in the stars brightness equivalent
to an eclipsing binary star system.
By measuring the size of the star, we get the
size of the planet.
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The Exoplanet Orbiting HD 189733
Using the CHARA Array, GSU graduate student Ellyn
Baines found an angular diameter for the star of
0.00038 arc seconds. This means the planet,
which was known to be about 17 the diameter of
the star, is about 20 larger than Jupiter. The
planet has a density of about 0.75 gm/cm3,
similar to Saturn.
This is the first direct measurement of the
diameter of an exoplanet
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Extrasolar Planet Distance Distribution
from exoplanets.org
AU from Parent Star
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A Plethora of Planets
In 1995, the Swiss astronomers Michel Mayor and
Didier Queloz found the first extrasolar
planetary system around the G2.5 IV star 51
Pegasi. The new planet orbits about the star with
a period of 4.2 days and has a minimum mass of
0.5 Jupiter masses. As of April 2008, there are
235 stars (other than the sun) containing 287
planets. See exoplanets.org and exoplanet.eu for
details about these systems. The big surprise
has been the presence of high mass planets, like
Jupiter, close to the parent star. This has
revolutionized thinking about the origin and
dynamical evolution of planetary systems.
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Extrasolar Planet Mass Distribution
from exoplanets.org
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Terrestrial Planet Finder NASAs planned missions
to find other Earthlike planets around nearby
stars starting in 2015
TPF-C is a coronagraphic imager that blocks
light from the central star in order to detect
planets surrounding it. TPF-C will be launched in
2014.
TPF-I is a interferometric imager that seeks to
directly detect earthlike planets around nearby
stars. TPF-I will be launched in 2020.
The dual TPF missions will detect and image
terrestrial planets around other stars and
explore spectroscopically the atmospheres of
those planets to search for signs of life. see
planetquest.jpl.nasa.gov/TPF/tpf_what_is.cfm for
more details
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Life in the Universe The Drake-Sagan Equation One
way of anticipating the frequency of life in the
Universe
N Ns. fp. fh. fl. fi. fc. fs   where Ns
Number of stars in the Milky Way 1011 fp
Fraction of those stars having planets 01
fh Fraction of planets that are habitable 0.1
(our system) fl Fraction of habitable
planets with life 01 fi Fraction of life
bearing planets with intelligent life 01 fc
Fraction of those intelligent civilizations
actively communicating 0...1 fs Fraction
of those communicating civilization that survive
01 N Number of communicating
civilizations in the Milky Way 11010   Numbers
can be estimated for each of these parameters
based upon optimistic or pessimistic assumptions
that indicate that N is 10 billion or only one
(us)!