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77 Cards in this Set

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Galaxy had to be ******* in shape
spiral (only 5 percent are spiral)
No-nos for location
can't be in a rich cluster - mergers and collisions would be too frequent
Needs for location
nearby dwarf galaxies to supply dust and gas for the Milky Way's spiral structure
Elliptical Galaxies are no-nos because....
no dust or gas or heavy elements to make a life-supporting planet
Irregular Galaxies are no-nos because....
too big - radiation destroys life

too small - same story as Elliptical Galaxies
define co-rotation point
At the co-rotation point the Sun remains stationary and out of a spiral arm.
Must be near but not inside *****
a spiral arm
Why it is bad to be inside the spiral arm (where most Milky Way stars are located)
the star densities are too high – the planetary orbits would be unstable
Only one star! Why?
1) Gravity from two or more stars would make stable planetary orbits impossible.
2) If no star - there would be no energy source
Must be a **** type star
G-type star
Why only a G-type star?
1) If hotter, UV would extinguish life
2) If cooler, would have to be so close that tidal effects of the star on the planet would slow the planet’s rotation
The right....
Hary Habitable zone
Gave (surface) Gravity
Rose Rotational period
Much Magnetic field
Heat source
Peed (water or some other liquid)
MUST BE IN THE HABITABLE ZONE Why?
(Water at the triple point), distance within 2%
MUST HAVE THE RIGHT SURFACE GRAVITY Why?
1) If too high, hydrogen and helium would be retained
2) If too low, the atmosphere would dissipate into space (within 2%)
MUST HAVE THE RIGHT ROTATIONAL PERIOD Why?
1) If too fast, circulational weather pattern would be too severe
2) If too slow, the day/night temperature variation would be too great
MUST HAVE A MAGNETIC FIELD Why?
Needed for protection from the Solar wind
MUST HAVE A CENTRAL HEAT SOURCE (AN UNUSUALLY LARGE CORE) TO DRIVE TECTONIC ACTIVITY Why?
The Earth’s surface would erode to the extent that life would not survive unless the Earth’s crust was constantly replenished.
MUST HAVE WATER (OR SOME OTHER LIQUID) Why?
To lubricate the tectonic activity
NEED A GIANT OUTER PLANET LIKE JUPITER Why?
It takes the hit from asteroids and comets eliminating catastrophes on Earth
NEED A LARGE MOON IN ORDER TO Why?
1) Stabilize the Earth’s axial tilt
2) Create tides which wash the Earth’s surface cleansing the oceans and mixing oxygen from the air into the water to support marine life.
HUGH ROSS
LISTS 322 unique characteristics of the Earth
Hugh says probability of finding life on another Earth (when calculated with one planet for Star) is ...
10 to the negative 304
Mercury/Venus are too **** to support life
hot
Earth was ****** for life
just right
Mars was ***** once but now too ***** for life
OK

cold
Jupiter, Saturn, Uranus, Neptune are too ***** to support life
cold
Optimal Temperature range for life is...
T<100 degrees C
T> 0 degrees C

since water is a great solvent
What sets planet temperatures?
Solar Radiation (Solar flux)
Albedo
Rotational Rate
Distance
Heat sinks on Earth
Chemical changes
Photosynthesis

D CHARPS
Assume that the dominant factor is stellar radiation (energy equation)
Total Energy (Absorbed) = Total Energy (radiated)
The zone in a stellar system where water is in liquid form (at least some of the time)
the habitable zone
Hertzsprung-Russell Diagram
y axis = luminosity
x axis = temperature
Most stars are **** stars
M
excluding M stars, about ***** of all the rest of stars are K stars
1/2
the range of distance from an M star that contains habitable life is very *****
small
M Star Problems
1)Habitable zone is VERY close to the star
2) Gravitational/tidal forces are much stronger here, so we expect tidal locking may develop this close (everything goes outwards towards the star)
More M Star Problems
M stars have very active magnetospheric storms and flares
Habitable Zones: O/B stars pros and cons
pros - Range in distance from the star is huge. We expect many planets in this range
cons - short life times
How long does an O star live?
428,000 years (biggest type of star)
How long does an A star live?
longer than an O star or B star
How long does a B star live?
longer than an O star but less than an A star
What stars are the likeliest targets in searching for extraterrestrial life?
Late F stars (F5)
G stars (yeah us!)
K stars
Where around these late F, G, and K stars do we look for life?
the habitable zone
Life on Venus?
1) Venus is MUCH hotter (by about 60K) than we expected
Due to its thick atmosphere and greenhouse gases
So … thick atmosphere can “ruin” a planet in the close end of the HZ or it can...
keep a planet just outside the distant end of the HZ “warm”
What about life on Europa/Enceladus ?
These moons seem to have liquid water (potentially in VERY large quantities)
What is Europa?
moon of Jupiter
What is Enceladus?
moon of Saturn
How did Europa get water on it?
At great distance from the nice warm sun and no atmosphere to trap surface heat, the very top is clearly solid ice. But thanks to internal heat from tidal forces, Europa appears to have a liquid layer
How did Enceladus get water on it?
But scientists have been surprisingly divided about whether the insides of Enceladus are liquid or solid ice, with a process called sublimation (solid turning directly to gas) generating the water vapor-filled plumes.
Most stars are in ******
binary systems
Could life live on a binary system?
1) maybe - going in an out of habitable zone would be tough on life
2) even if planet stabilized between 2, then it would probably be too far away to still be in the habitable zone
Stars in the inner galaxy are....
densely packed - lots of issues with supernovaes and such
stars in the outer galaxy are less *******
"chemically evolved" - not that much C or O
If we assume temperature is dominated by sun/star-light, then....
the HZ can be calculated for any given star
Likely star types for life are....
F, G, and K stars
A vortex coronagraph
based on the fact that, due the extreme distances of the stars, we can treat their light as being coherent. Using diffraction to blank out the central images we can see. You then rotate the diffractor around a 360 degree circle to reveal the planets near it.
Alex Wolczan
In 1992 he discovered 2 (now 3) planets around a neutron star (seemed weird tho, maybe remnants from supernova)
Kepler described
3 “laws” of planetary motion (for our solar system)
Newton later used his physical laws of motion to show...
WHY Kepler’s rules for planet motion worked
Kepler’s First Law
1) Planet orbits are ELLIPSES
2) The sun/star is at one “focus” of the ellipse
3) Both the planet and the star orbit the center of mass
4) The distance from the center to the focus is c=ae where e is the “eccentricity”
What is an ellipsis?
Circles are ellipses with eccentricity=0 (both foci at center)
Kepler's Second Law
Planet motion sweeps out equal areas of the ellipse in equal time
Meaning … planet moves faster when it is closer to the star and slower when it is farther away
Kepler’s Third Law
a3/P2 = Mtot
a = semi-major axis of the ellipse (AU)
P = period of the orbit (years)
Mtot = total mass of the system (solar masses)
What does a represent in Kepler's Third Law?
a = semi-major axis of the ellipse (AU)
What does P represent in Kepler's Third Law?
period of the orbit (years)
What does Mtot mean in Kepler's Third Law?
Mtot = total mass of the system (solar masses)
For a star/planet system, the ***** does most of the moving
planet
The BaryCenter is the **** of the solar system
center of mass
Radial Velocity Planet Searches
1) So … need a speedometer to measure star velocity versus time
To a precision of a few meters per second!
Across distances of many light years!!!
How? Doppler shift of spectral lines
***** has biggest reflex velocity effect on the Sun
Jupiter
51 Pegasi
In 1995, Mayor & Queloz announce the discovery of an orbital signature with amplitude = 50 m/s in a 4.23-day period around star 51 Pegasi
Mass = 0.5 MJUP  First extra-solar planet
At 51 Pegasi's location...
extremely hot! Size of Jupiter but closer to the sun than Mercury O_O
Geoff Marcy & Paul Butler
confirmed Pegasi 51
most extra-solar planets known today are
"Hot Jupiters"
“MARVELS” (Multi-object Apache Point Observatory Radial Velocity Exoplanet Large-area Survey)
is the UF’s program launched in 2008 that promises to be one of the most prolific of all exoplanet hunting programs.
How many known extra-solar planets are there?
763
All of this has happened in about 20 years –
someone currently finds a new planet every couple of weeks or less