Download PSC1010 Introduction to Astronomy Quiz #3 Review Thursday 3

PSC1010 Introduction to Astronomy
Quiz #3 Review
Thursday 3 November 2011
Quiz #3 will cover the following material
Chapter 5 Telescopes
Chapter 8 Solar System Structure and Formation
Chapter 9 Inner, or Terrestrial Planets (will cover on Tuesday)
Chapter 10 Outer, or Jovian Planets
(will cover on Tuesday)
Astronomy Picture of the Day from
Tuesday 18 October 2011 through and including
Tuesday 1 November 2011
---------------------------------------------------------------------------------------What to Know from Chapter 8, Solar System Structure and Formation
Basic components of solar system, and how the solar system formation theory
arose from those components.
-Basic Components and Features of the Solar System:
The Sun, a star, is 700 times more massive than everything else in the solar system combined.
The Planets. Know their names and their order. Going from closest to the Sun to furthest:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
All planets orbit (travel around the Sun)
in the same direction (counter-clockwise looking down on
north poles, where north pole of rotation axis is defined by right-hand-rule).
Most planets rotate (spin on their own rotation axis) in the same direction
(counter-clockwise). The rotation axis of Venus is flipped, so it rotates
clockwise when viewing the Solar System looking down on the north poles of
most other planets. The North-South rotation axis of Uranus lies in the plane
of its orbit. These two anomalies are likely due to impacts with planetesimals
(asteroids) after they formed.
Most moons orbit their planets in the counter-clockwise direction when looking down on
North poles, in the same direction that the planets orbit the Sun.
Know the major differences between Inner (Terrestrial) and Outer (Jovian) planets.
-Inner planets are: rocky, compact, dense, low mass, have few if any moons, thin atmosphere
-Outer planets are: gaseous+liquid+small rocky core, not dense, high mass, have many moons,
thick atmosphere
Other components of Solar System:
-asteroid belt -- ring of rocky debris orbiting the sun in a ring betwwen Mars and Jupiter
-Kuiper Belt
-- ring or rocky/icy debris orbiting the sun out beyond Neptune's orbit
Pluto's orbit is within (at the inner edge of) the Kuiper belt
-Oort Cloud
-- a sphere of icy/rocky bodies (comets) surrounding the Solar System,
comets from this cloud orbit the Sun in random directions with
very elongated elliptical orbits
Planets and asteroid/Kuiper belts all orbit the Sun in approximately the same plane
(the ecliptic planes) and in the same direction.
-How is the Age of the Earth / Solar System estimated
Radiometric dating rocks on Earth and meteorites that fall to Earth
Radiometric dating compares measurments of the amounts of different radioactive
isotopes in the sample with well determined knowledge of the decay rates of
the isotopes to give a minimum age of the sample
A minimum age means the rock is equal to or older than the derived age.
The oldest measured age for a rock sample is 4.6 billion years,
so the Earth is no younger than 4.6 billion years old.
This matches age estimates for the Sun for stellar evolution theory
-Solar System Formation (Know how the observed features described above led to the theory of
Solar System formation)
Supernova or (many) supernovae trigger rotating gas+dust cloud collapse in the
interstellar medium of the Galaxy.
The cloud's self-gravity causes it to contract. The cloud rotation increases, just
as an ice-skater rotates faster with arms tucked-in, rather than spread out.
As the rotation speed increases, the spherical cloud flattens into a disk.
Such disks are observed throughout our galaxy, the Milky Way.
Continued self-gravitation (infall) leads to formation of a bulge at the center of the disk.
Friction heats up the infalling gas+dust.
As the bulge/core get more massive and increases its self-gravity, it starts to accrete
(or attract) even more gas+dust: this is in addition to infall
---> more gas+dust means more mass means more friction and accretion means more mass
---> eventually, when the core mass, pressure and temperature are high enough,
nuclear fusion (hydrogen --> helium) ignites...a star is born!
The rotating/collapsing cloud formation model comes from the observation that the planets
all orbit the Sun in nearly the same plane and have the same orbital direction.
Why are there two types of planets (inner: rocky and small; outer: gaseous and massive)?
That depends on the temperature throughout the solar nebula.
-Iron and silicates (silicon+oxygen, or rocks) condense (change from gas to solid) at very high
temperatures (over 500K)
-note: water freezes at 273K, room temperature is 300K, water boils at 373K
-Water, ethane, methane, ammonia (hydrogen, carbon, nitrogen)
condense at low temperatures (under 500K)
--> since gaseous iron and silicates can condense at 500K and below, rocks
can form throughout the solar system (wherever it is 500K or less)
--> Water, ethane, methane, ammonia may only condense from gas to liquid or solid
where it is cool, far from the sun
--> Therefore, inner planets are rocky; outer planets are mostly gas and liquid with
rocky cores
--> Since more elements may condense where the nebula is cool, there are more planetbuilding raw materials (by 10x) further from the Sun.
Therefore, planets further from the Sun can be larger.
General planet formation
-Condensed clumps within the nebula (small planetesimals [comets or asteroids]) will
collide and stick together, forming larger clumps
-In the outer solar nebula, the clumps will get massive enough to accrete (attract)
more gas around them
-Most of the gas in the solar nebula was swept up this way
How did the planets get their moons?
Earth: impact by Mars-sized object. Debris self-gravitated to form moon
Outer planets: planetisimal capture
How did the planets get their atmospheres?
Inner planets: volcanic activity released interior gases to the surface,
captured gas from comets that vaporized on impact
Outer planets: swept-up hydrogen from solar nebula
Planet-hunting techniques (looking for other solar systems):
[planets in other solar systems are called exoplanets]
1) direct imaging (very difficult), a planet does not emit its own light,
it reflects the light emitted by the star it orbits
2) Doppler shift of central star
-gravitational tug of orbiting planet makes star orbit the center-of-mass
(ellipse focus) of the star-planet system
-observe doppler shift of star (redshift when it moves away from us,
blueshift when it moves toward us)
-doppler shift cycle gives period
-spectrum gives mass of star
-Newton's modified Kepler III gives distance between star and planet
-spectrum gives temperature of star
--> can find out if planet is in the so-called Goldilocks zone,
distance from star where temperature is right for surface water to exist
--> actual detection of water is very difficult,
exoplanets are faint (hard to get spectra), no confirmations of water on
expoplanets yet.
3) Gravitational Lensing
--> planet orbiting a star bends light of a background star in a periodic way
4) Planetary Transits (Kepler satellite mission)
-as a planet passes in front of the star, the star-light is dimmed
-light curve gives orbital period
-stellar spectrum gives size (diameter), mass and temperature of star
-shape of light curve gives planet size and tilt of orbit relative to
our line of sight
--> method is more suited to finding massive (Jupiter-sized) planets orbiting
close to their host star (short period) than earth-sized planets orbiting
1 AU from the host star
---------------------------------------------------------------------------------------What to Know from Chapter 9, The Inner (Terrestrial) Planets
-components of innter planets (core, mantle, crust)
-larger planets cool slower after formation
-surface geological activity is determined by interior
temperature of planet
-estimate time of last surface activity by counting impact craters
(geological activity [crustal plate movement, folded mountains, volcanic activity, erosion]
will smooth over impact craters)
-concept of young surface (craters smoothed over, surface
crust replaced by geological activity or changed by erosion) and
old surface (heavily cratered).
Differences among inner planets, especially differences in atmospheres.
Mercury - no moons, no atmosphere (probably never had one; likely too small and
too hot [atmosphere gas-particle velocity would exceed Mercury's
escape velocity and atmosphere would dissipate]
- many craters --> low or no geological activity <-- low mass planet, cooled faster
than other planets
- may have water ice inside shadow of craters near poles
- magnetic field detected by satellites
Venus - very dense, high pressure 95% carbon-dioxide atmosphere, sulfuric acid rain clouds.
- runaway greenhouse effect (hottest planet in solar system)
1) Sun heats planet
2) planet's atmosphere traps infrared radiation from planet
3) atmosphere heats up
Any water that may have existed on Venus in the past would have risen high into
its atmosphere, been photo-dissacociated by sunlight, and is now gone
- about as geologically active as earth (same mass as earth)
- no magnetic field
Earth - atmosphere is mostly nitrogen and oxygen with only 0.03% carbon-dioxide
- erosion and other geological activity smooth over impact craters
- magnetic field
Mars
- mostly carbon-dioxide atmosphere, but very tenuous (not dense) and low pressure
--> no greenhouse effect
- evidence of past
1) geological activity, volcanoes, mountains, canyons
2) magnetic field
3) surface water
Note in planetary evolution slide
- evolutionary stage of planet correlates with mass least massive planets are geologically dead sooner
Why is the atmosphere of Earth different from that of Venus and Mars?
(see class slides for details)
- water (H20) rain removes carbon-dioxide from atmosphere: (locks it (carbonic acid)
in rocks, C02 in oceans becomes clam-shells (calcium carbonate)
- role of biology: plants break down water and carbon dioxide during
photosynthesis, releasing oxygen into the atmosphere
- geological activity (volcano) can melt rock in the Earth's mantle
and re-release carbon dioxide into the atmosphere
----------------------------------------------------------------------------------------How do we know the composition of the components of the solar system?
Planet atmospheres, comet tails, collapsing proto-star clouds, etc.
1) spectroscopy for all components
2) probes that are equipped with spectrographs and visit the planets
---------------------------------------------------------------------------------------------------------------------------------------------What to know from Chapter 10 The Outer Planets
Jupiter, Saturn, Uranus, Neptune
-same overall composition, same relative amounts of atomic elements
as the Sun
-large size and high mass
-thick, tenuous atmospheres
-rocky cores
-all have rings
-all have many moons
Where to the rings come from?
-Rings are composed of small particles of ice, rock, and dust
-Ring material eventually falls into a planets atmosphere.
-Rings are replenished by new material from colliding moons
or moons ripped apart by tidal forces.
What are tidal forces?
-Force on the near size of an object is much stronger
than the force on its far side.
-Roche limit: an object held together by its own gravitity,
(such as a moon) will be ripped apart by tidal forces if
it strays within the Roche limit of a larger body (like a planet).
The Roche limit is 2.44 times the radius of the planet.
--Does not apply to objects held together by chemical bonds
or to man-made satellites
Jupter Emits Radio Waves
-The radio waves are generated by charged particles trapped and
accelerated within Jupiter's magnetic field. The particles are
supplied by the solar wind and by Jupiter's volcanically active
moon Iol
--The tidal forces exterted by Jupiter on Io are responsible for
heating that moon's interior; that interior heat drives Io's
surface geological activity, including the volcanoes.
-When the trapped particles strike Jupiter's atmosphere near the
poles, aurorae are producted. The auroral lights are line emission
produced by ionized gas in a planet's upper atmosphere; the gas is
ionized (atoms lose outer electron(s)) when the charged particles
trapped in the magnetic field collide with the atmospheric gases.
If the outer planets have the same composition, why don't they all
look the same in visible light images?
-Jupiter shows multi-colored bands (produced by wind shear [adjacent
bands have different wind speeds and possibly directions])
-Jupiter shows large storms (hurricanes) shaped like oval spots.
-Saturn is tan or yellowish with faint/featureless bands
-Uranus and Neptune are blue; Uranus is featureless, Neptune shows
some bands and spots
-->Each planet's temperature determines its appearance:
-The cloud-tops of Jupiter's atmosphere contain hydrogen, helium,
methane, ammonia, and water; that mixture of gases in Jupiter's
upper atmosphere are responsible for its multi-colored appearance.
-Saturn is farther from the Sun than Jupiter and therefore colder;
it has ammonia ice particles in its upper atmosphere. These
particles give the planet its generally featureless
tan appearance.
-Uranus and Neptune are even further from the sun and yet colder.
The methane in their upper atmospheres absorbs red light from the
Sun and reflects the blue light that we observe with visible-light telescopes.
--> In infrared light images all the outer planets show bands due to
wind shear and storms appear as hot spots. Infrared light from
the Sun can penetrate the screen of the upper atmosphere and
reflect back to us from lower layers in those planets'
atmospheres.
Saturn's moon Titan has an atmosphere.
-Titan has high mass, high surface gravity, and high escape velocity
-Saturn+Titan are far from the Sun and are cold
-A cold atmosphere has a low gas particle speed, less than the
escape velocity of Titan.