Study Guide for Test #3

Dr. J. R. Webb

Solar Astronomy

Chapter 7. Our Solar System.

1. Physical structure of Solar System.

• The Sun – Center of the Solar System and responsible for all of the energy and light, the focus of every planets orbit, dominates in mass.
• The Planets, meteoroids, comets, asteroids – Left over debris from the formation of the Sun.
• “Inner planets” – terrestrial or rocky type planets. Mercury, Venus, Earth and Mars.
• “Outer Planets”- Jovian or gaseous planets. Jupiter, Saturn, Uranus, Neptune.
• “Is it really a planet” – icy body. Pluto.

2. Planetary Orbits: Most planets lie close to the ecliptic plane, most planets’ orbit are close to circular. Except: Pluto! Inclination = 17^o , eccentricity = 0.248.

Sometimes Pluto is closer to the Sun than Neptune!

3. Other members of the Solar System: Asteroids, comets, planetary Moons.
• Asteroids – rocky and icy bodies, orbit in a band between Mars and Jupiter primarily, but some orbit among the other planets!
• Comets – Thought to be mostly icy bodies, usually highly eccentric elliptical or parabolic orbits.
• Some planetary Moons are bigger than Mercury.

4. Formation of the Solar System – We have to explain formation and composition of the Sun, the planets, and the configuration of the Solar System.

• Sun forms by gravitational collapse
• Planets form out of left over gas and dust, terrestrial planets close in since the temperature in the Solar nebula is higher near the center, and condensation of lighter elements is high. Gases get pushed out early, heavier elements condense into solids and remain in the inner regions – form terrestrial planets.
• Conservation of Angular Momentum specifies that the all of the planets should be rotating in the same direction and spinning in the same direction as the Sun rotates.
• Inner planets form by accretion, outer planets form by accretion and capture of gas.

Chapter 9. The Living Earth.

1. Earth Data: Equatorial Diameter = 12,756 Km. Mean Density = 5500 Kg/m³, escape velocity = 11.2 km/sec, mass = 5.976x10²⁴ Kg.
2. Earth consists of: Atmosphere, Crust, Mantle, outer core, inner core.
• Crust – made up and minerals and rocks.
• Rocks – sedimentary, Igneous, metamorphic.

3. Structure of the Earth is studied by monitoring earthquakes.

· L-Waves - Rolling motion of surface

· P-Waves – Longitudinal Waves – (primary)

· S-Waves – Transverse Waves – do not propagate through liquid. Travel slower than P waves.

4. Melting point curve – Temp versus radius of Earth.

5. Surface Processes –

· Plate tectonics, subduction zones, volcanoes, mountain building, etc.

6. Earth’s Atmosphere – troposphere, stratosphere, mesosphere, thermosphere, exosphere, magnetosphere. Atmosphere:N,O,CO₂, (ozone in stratosphere)
7. Earth’s Magnetic Field – Generated by rotating, liquid outer core.

Chapter 10 . Our Barren Moon

1. Moon is 81 times smaller than the Earth, geologically dead (no volcanoes or crustal plates.
2. Moon is in synchronous rotation: 1 rotational period = 1 sidereal orbital period. Result = we always see the same side of the Moon.
3. We actually see a little over 50% of lunar surface ~ 59% due to libration.
• Inclination of lunar equator to ecliptic ~ 5^o 9^’
• Moon’s orbital eccentricity ~ 0.055
4. Lunar mean density = 3340 Kg/m³, surface gravity = 0.165 g (g = accel. of gravity on Earth=9.8 m/s²)
5. Types of Lunar Terrain – Maria, Terrae or highlands, Mountains.

· Maria – prominent, dark flat areas formed by lava flows which filled low-lying regions ~ 3.5 billion years ago. (2-5 km below average level)

· Terrae – 5 km above average level, lighter than Maria.

· Mountains – mountains formed by impacts of asteroids and meteors, not geologic processes.

· Far side – almost all cratered Terrae, only one small Maria!

6. Structure of the Moon –

· No current magnetic field – possibly has a small iron-rich core, but cooled long ago.

· Near-side crust is much thinner than the far-side crust, near side ~ 60 km, far side ~ 100 km. Explains absence of Maria on far side!

· Solid mantle ~ 800 km thick

· Core less than 700 km thick.

· Lunar surface covered with pulverized rocks (regolith), but since no atmosphere or water > No Weathering! Craters remain undisturbed over geologic ages.

7. Lunar exploration –

· Un-manned landings –Surveyors (USA) – took pictures

· Apollo Lunar Missions – (don’t memorize this for the test, just wanted you to have this info!!!)

Apollo 11 landed July 20, 1969 in Mare Tranquillitatis

Apollo 12 landed Nov. 19, 1969 in Oceanus Procellarum

Apollo 13 didn’t land (see tom Hanks movie!!)

Apollo 14 landed Jan. 31, 1971 in a crater named Fra Mauro

Apollo 15 landed July 30, 1971 in a ridge called Hadley-Apennines

Apollo 16 landed April 21, 1972 in Crater Descartes

Apollo 17 landed Dec. 11, 1972 in Maria Taurus-Littrow valley.

8. Lunar Rocks –

· Formed 3 to 4.5 billion years ago

· No sedimentary rocks, no true metamorphic rocks, all igneous

· Some rocks modified by meteor impacts!

· Maria – basalt rock, highlands or Terrae – anorthosite

9. Lunar formation –

· Moon formed as a result of the collision of a Mars-sized object with the Earth. The Earth was liquefied, and part of the Earth and part of the projectile was ejected, and reformed together to form the Moon. This occurred very early in the history of the solar system, within first 0.1 billion years

Chapter 11. Sun-Scortched Mercury

1. Terrestrial-type planet, closest to the Sun, men density = 5420 Kg/m³

2. orbital eccentricity ~ 0.206, inclination of orbit ~ 7⁰.

3. Favorable elongation ~ 28^o, unfavorable elongation ~ 18^o

4. P_sidereal = 88 days, P_synodic= 116 days

5. Mercury rotates slowly (59 days) and is a 3-to-2 spin-orbit coupling. This means it rotates three times for every two orbits. Dynamically stable but very rare.

6. Mariner 10 visited Mercury and photographed it. Mariner 10 carried TV cameras, infrared radiometer to measure temperature, UV spectrometer (search for atmosphere gases), magnetometer to measure magnetic field, charged particle detector to measure Solar wind.

7. Pictures revealed “Scarps”, Wrinkling of crust due to the fact it cooled and solidified before the core did. Subsequent core contraction caused the surface to break and fold creating steep cliffs we call scarps.

8. Also showed Caloris Basin (an impact crater) and diametrically opposite (on the other side of the planet) the Marius Hills, caused by convergence of seismic waves from the Caloris Impact!

9. Compressed density – Mass/volume

Un-compressed density - Mass/(Volume it would have if no gravity were present) r_compressed = 5420 Kg/m³, r_uncompressed = 5,300 Kg/m³, Earth’s un-compressed density = 4000 Kg/m³, therefore, Mercury contains a higher proportion of than the Earth. Iron core = ¾ planets diameter.

10. Has a magnetic field 1/100 that of Earth,

11. No atmosphere, surface temperature facing sun is ~700K.

Chapter 11. Cloud-Covered Venus

1.Venus is nearly Earth’s twin, similar mass, diameter, average density.

2. Venus’ surface completely shrouded by clouds. Highly reflective so it is the

brightest “star” in the night sky. Morning and Evening star!

3. Venus rotates “retrograde” or backward relative to the other planets. This was discovered by using Doppler radar to measure the surface velocity.

4. Orbital period = 224.7 days, rotational period = 243.01 days

5. We knew about Venus’ atmosphere by observing the “Ring” around the planet when backlit from the Sun due to atmospheric refraction of sunlight.

6. Venus’ surface is extremely hot, T_surface = 750 K ~ 900^o F due to Greenhouse effect of the CO₂ in its atmosphere. IR radiation is trapped inside by CO₂.

7. Venus has no measurable magnetic field although it should still have a liquid core – probably because it rotates so slowly!

8. Venus’ atmosphere has several could layers, 96% of atmosphere is CO₂, 4% is Nitrogen. Upper clouds contain Sulfur dust, lower clouds contain sulfuric acid droplets. Interactions of sulfuric acid with surface rocks creates – hydrofluoric, hydrochloric, and fluorosulfuric acid!

9. There is evidence for significant volcavic action occurring today.

10. Surface has 2 “continents, Ishtar Terra (size of Australia) and Aphrodite Terra (1/2 area of Africa)

11. Volcano Maxwell Montes -12 km high mountain (Mt. Everest is 9 km high). The base is Maxwell Montes is the size of Colorado!

Chapter 11. MARS

1.Terrestrial planet that is smaller in size than the Earth.

2. Christian Huyghens in 1659 determined Mars rotated with a period of ~24

hours!!! Nearly identical to the Earth.

3. “Canals” controversy.

4. Mars has an extremely thin atmosphere is 95% CO₂. P = 5-10 milli-bars.

5. Mariner 9 went into orbit around Mars and saw:

· Olympus Mons – 24 km high extinct Volcano

· Valles Marineris – 3000 km long rift valley

· Dry river beds!

· Martian Polar caps made of frozen CO₂ AND frozen H₂O (water)!!

6. Viking Spacecraft soft-Landed on the surface and obtained data about climate, atmosphere and surface geology.