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Astronomy 305/Frontiers in Astronomy
Class web site:
http://glast.sonoma.edu/~lynnc/courses/a305
Office: Darwin 329A and NASA E/PO
(707) 664-2655
Best way to reach me:
[email protected]
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Prof. Lynn Cominsky
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Astrobiology Questions (3 weeks)
Is there life elsewhere in our Solar
system?
 Are Earth-like planets common?
 Are we alone?
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Group 6
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Are Earth-like planets common?
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Question to ponder:
When will Voyager get to the next star? It was
launched in 1977 and has just passed Pluto.
A) 2020 AD
B) 8200 AD
C) 82,000 AD
D) 182,000 AD
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Answer
Voyager is travelling about 37,000 mph,
which is about c/20000
 The nearest star (Proxima Centauri) is
about 4 light years away
 It will therefore take about 80,000
years to reach Proxima Centauri
 The correct answer is therefore C
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Planets around other stars
Over 100 planets around other stars are known
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Planets around other stars
PSR 1257+12 (a radio pulsar, Wolczan 1995)
3 objects orbiting this stellar corpse
1 is the size of the Moon
2 are the size of the Earth
probably formed after the supernova explosion that made
the pulsar
51 Pegasi (Sun-like star, Mayor and Queloz 1996)
 at least one object, about 1/2 of Jupiter
 orbit of only 4 days
 closer to star than Mercury, so very hot
 42 light years from Earth
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Planets around other stars
70 Virginis (Sun-like star, Marcy and Butler 1996)
 116 day orbit
 9 Jupiter masses (1 Jupiter = 317 Earth masses)
 temperature of planet may allow liquid water to exist
 78 light years from Earth
47 Ursae Majoris (Marcy and Butler 1996)
 1100 day orbit
 3 Jupiter masses
 temperature of planet may allow liquid water to exist
 44 light years from Earth
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Another solar system
Upsilon Andromedae: Multiple planet solar system
discovered by Marcy et al.
a) 4.6 d
b) 240 d
c) 1313 d
Ups And
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How they find extra-solar planets
Stars are too bright to see reflected light from
planets directly
 Unseen planet causes star to wobble as it
orbits – star’s light is Doppler shifted
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Doppler Shift
Wavelength is shorter when approaching
Stationary waves
Wavelength is longer when receding
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Doppler Shift
Comparison of laboratory to blue-shifted
object
Comparison of laboratory to red-shifted object
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Doppler Shift

Doppler shift song by AstroCapella
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Other methods:

Astrometry – measuring the exact position of
a star as it wobbles
Hipparcos was an ESA satellite operational from 1989-93
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Other methods:

Photometry – measuring the change in
brightness of a star as a planet transits in
front of it, obscuring some of the light (~2%)
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The first transiting planet
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HD209548 – a visualization by Aurore Simonnet
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The first transiting planet
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STARE project found the first transit in
HD209548 – Brown and Charbonneau 1999
The planet’s mass is 63% of Jupiter (about 200
Earth masses) with radius 1.3 times Jupiter 
density 0.39 g/cm3 (< water!)
It transits the star every 3.5 days
Its atmosphere is very hot (1100oC) since it is
only 6.4 million km from the star
When the planet passed in front of the star, the
star’s light passed through the planet’s
atmosphere and sodium was observed by HST
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Saturn mass planets (95 times Earth)
Both planets are very close to their stars This makes them easier to detect
 If each planet orbited the Earth’s Sun:
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Latest news (7/03)
(See exoplanets.org)
110 planets are now known outside our solar
system
 Earlier searches preferentially found closer
orbiting planets, more massive planets and
eccentric orbits (“hot Jupiters”) – now smaller
planets are being found in orbits that are closer
and more circular
 Jupiter-analog found around HD70642
 Sub-Saturn planet found around HD 3651
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Iron abundance vs. planets
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The probability that a star harbors a planet
depends on the star's metal content.
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Inventing Alien Life forms

This activity is from the Univ. of Washington
http://www.astro.washington.edu/labs/clearinghouse
/activities/aliens.html
Take one dice for each group of 2 students
and try the evolution experiment to create
your own alien. The rolling of the dice
reproduces the random elements in evolution.
 When you have finished, draw a picture of
your alien and give it a a name
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Inventing Alien Life forms

Write a paragraph that has the following
information:
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Describe the environment your creature needs to
survive.
Where in our solar system would you be most
likely to find such a creature?
What sort of food source might your creature
need?
Is your creature alone in its environment? If not,
how does it coexist with other species?
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Web Resources

Voyager mission
http://vraptor.jpl.nasa.gov/voyager/voyager.html
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Extra-solar planet searches
http://exoplanets.org

STARE:
http://www.hao.ucar.edu/public/research/stare/stare.
html
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Latest news: (and a cool interactive)
http://planetquest.jpl.nasa.gov/news/tau1_gruis.html

Hipparcos Space Astrometry Mission
http://astro.estec.esa.nl/Hipparcos/
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