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UA / Astronomy / ay 101 / When did the planets form?

When did the planets form?

When did the planets form?


School: University of Alabama - Tuscaloosa
Department: Astronomy
Course: Intro To Astronomy
Professor: Ronald buta
Term: Spring 2017
Tags: astronomy, solar system, planets, moon, asteroids, comets, and Alabama
Cost: 50
Name: Exam 2 study guide
Description: Outline of all chapters in Exam 2 and clicker questions with answers.
Uploaded: 10/13/2017
18 Pages 215 Views 3 Unlocks

EXAM 2 Study Guide AY 101  

When did the planets form?

Chapter 6 

1) Solar System (SS) – Sun, 8 planets (4 terrestrial, 4 Jovian), dwarf planets, asteroids, comets 2) Sun – >99.9% of total mass of Solar System, 98-99% hydrogen/helium 3) Terrestrial planets – small, near Sun, rock/metal, high density, no/few moons, no rings a) Mercury  

b) Venus

c) Earth  

d) Mars  

4) Jovian planets – large, far from Sun, gaseous (mostly H/He/hydrogen compounds with  small rock/metal cores), low density, many moons, ring system

a) Jupiter  

b) Saturn  

c) Uranus  

d) Neptune  

5) Asteroids – small, rocky/metal objects mostly in asteroid belt between Mars and Jupiter  (not remains of shattered planet!)

a) Asteroids are the planetismals that never formed into full planets  

What key quality is responsible for the moon and mercury being geologically dead?

b) Most asteroids are found in the asteroid belt between Mars and Jupiter  6) Comets – icy bodies beyond Neptune in Kuiper belt (40-100 AU) or Oort cloud (~50,000  AU)

a) Formed outside frost line  

7) Rules of Solar System I: all planets orbit Sun in same direction in same plane (most planets  rotate in same orientation too)

a) Motion of large bodies: all large bodies in the Solar system orbit in the same direction as  the Sun rotates and in nearly the same plane.  

b) Planets do not orbit in random directions or random inclinations, but in nearly the same  plane (like a flat pancake)

c) EXCEPTION: Uranus rotates on its side and Venus rotates backwards (counter  clockwise), some moons also have unusual orbits  

What does the lack of craters on io tell us?

If you want to learn more check out What is the average violent age in winsconsin?

8) Rules of Solar System II: planets divided into inner terrestrial and outer Jovian planets a) Inside frost line: small metal/rock planets form – the terrestrial planets and asteroids i) Gravity of terrestrials too weak to draw in hydrogen/helium gas

b) Outside the frost line: large planets form – the Jovians, plus comets

i) The gravity of ice and rock in large Jovian planetesimals strong enough to draw in  available H and He gas  ???? grow big (ice/rock/metal core with large H/He gas  envelope)

9) Rules of Solar System III: asteroids, comets exist Don't forget about the age old question of Why does innovation matter?

a) Unused leftovers from the accretion process

b) Rocky/metal asteroids inside frost line

c) Icy comets (with some rock/metal) outside frost line

10) Exceptions: Venus and Uranus’s strange rotation, Earth’s large Moon, water on Earth a) Explained in #17  

11) Nebular theory best describes formation of Solar System

a) Nebular Theory: states that our solar system formed from the gravitational collapse of a  giant interstellar gas cloud (the solar nebula)  

b) Formation theory must explain:

i) Patterns of motion of the large bodies  

ii) Existence of two types of planets  

iii) Existence of smaller bodies  

iv) Notable exceptions to usual patterns  

12) See Summary of Solar System Formation earlier in this lecture  ???? conservation of angular  momentum, energy play an important role, dust ???? planetesimal ???? planet a) Initial large (1 light year diameter) barely rotating gas cloud begins to collapse  gravitationally. Don't forget about the age old question of How do you draw a lewis structure?

b) Cloud spins up (conserving angular momentum) and flattens (due to collisions) as it  collapses.

c) Left with gas in a rapidly-rotating, thin, mostly circular pancake-shaped disk. d) Due to temperature gradient, rock/metal condenses everywhere in Solar System, while  hydrogen compounds only condense to solids (ices) beyond frost line.

e) Planets grow via accretion from dust ???? planetesimals ???? planets.

f) Outer large planetesimals large enough to accrete a lot of hydrogen/helium ???? form  mini-Solar Systems with moons. Don't forget about the age old question of What was hamilton's report on public credit?

g) Solar wind (when Sun turns ‘on’) clears out remaining hydrogen/helium gas to stop  further planet growth.

h) Asteroids/comets leftover unused bits and pieces that didn’t accrete onto larger  planets.

13) Inside frost line only rock and metal could condense (terrestrial planets + asteroids),  outside frost line rock/metal/hydrogen compounds (ices) could also condense (Jovians +  comets)

a) Jovian planets do have rock and metal in them though  

b) Frost line is between asteroid belt and Jupiter  

14) As Jovians grew via accretion, they attracted large amounts of H/He and grew very large a) Solar wind stopped their growth by blowing away H/He gas  Don't forget about the age old question of What is the employer's payroll taxes?

15) Jovians acted like mini-Solar Systems ???? moon systems

a) Jovians had their own accretion disks which went to form moons  

16) Planet growth ended when young Sun turned “on” and generated a solar wind that blew  away remaining gas

a) This stopped Jupiter from getting bigger  

17) “Exceptions” believed to be caused by an early “Period of Heavy Bombardment” – large  bodies hit Venus, Uranus (changing rotation), and Earth (stripped matter formed Moon,  water brought to Earth by comets)

a) Period of Heavy Bombardment caused many big collisions to lead to exceptions to the  rules  Don't forget about the age old question of What is the exact speed of sound?

b) Odd rotation of Venus and Uranus

i) Giant impacts might explain the different rotation axes of Venus and Uranus

ii) Each were smacked at some point during the period of heavy bombardment  c) Origin of Earths water  

i) Water may have come to Earth by the way of Icy planetismals (comets) that formed  beyond the frost line and collided with Earth  

d) Earth’s large moon  

i) Giant impact stripped matter from Earth’s crust, stripped matter began to orbit and  then accreted into moon  

18) Age of Earth/Moon determined from radiometric dating (for example, Potassium-40 turns  slowly into Argon-40), NOT carbon-14 dating (half-life for decay is way too short) a) We cannot find the age of a planet, but we can find the ages of the rocks that make it up  b) Determine this by analyzing the proportions of various atoms and isotopes within it  

i) Isotopes: atoms with the same number of protons but different number of neutrons  c) Radioactive decay:  

i) Some isotopes decay into other nuclei at a predictable rate  

ii) A half-life is the time is takes for half of the nuclei in a substance to decay  d) When did the planets form?

i) Planets probably formed 4.5 billion year ago  

ii) Oldest meteorites are 4.55 billion years’ old  

iii) Oldest moon rocks are 4.4 billion years’ old  

Chapter 7 

1) Terrestrial planets have radically different geologies, atmospheres despite common origin  inside frost line

a) Different geological activity or lack of activity causes differences in terrestrial planets  b) Geological activity caused by planets internal heat***

2) Core (high density iron/nickel) ???? mantle (moderate density silicate rocks) ???? crust (low  density rocks)

3) When planets were still molten, denser material sunk to the center ???? called  differentiation

a) Differentiation:

i) Gravity pulls high-density material to center  

ii) Lower-density material rises to surface  

iii) happened when planet was still liquid/ molten  

4) Lithosphere  

a) crust + outer part of mantle – cool rigid rock that floats on top of soft, warm rock of  inner part of mantle

b) can be broken into plates  

5) A planet’s internal heat determines level of geological activity

a) Rock heated by radioactivity in core  

b) Heat moved through mantle by convection  

i) Convection: hot rock rises, cool rock falls  

ii) One convection cycle takes 100 million years on Earth  

c) Why heat matters:  

i) Once internal heat is gone, the once soft hot rock cools off and lithosphere grows  thicker and thicker  

ii) Cold rocks will not flow  

iii) No more geological activity such as volcanoes  

(1) This is what has happened to Mercury, the moon and what is happening to Mars  now.  

6) Early times: differentiation + accretion ???? heat

(1) Now: radioactive decay in core ???? heat

7) Size is most important factor in determining how long a planet’s interior stays hot; when  heat is gone, geological activity is gone, rock hardens, atmosphere goes away a) Smaller worlds cool off faster and solidify earlier  

b) Moon and Mercury are geologically dead because they have no more internal heat*** c) Heat content depends on volume  

d) Loss of heat through radiation depends on surface area  

8) Impact cratering, volcanism, tectonics, erosion all shape the surfaces of worlds

a) Impact cratering

i) Impacts by asteroids or comets

ii) Most cratering happened soon after the solar system formed (period of Heavy  Bombardment)  

iii) Craters are about 10 times wider then object that made them  

b) Volcanism

i) Eruption of molten rock onto surface

ii) Happens when molten rock (magma) finds a path through crack in lithosphere to the  surface  

iii) Molten rock is called lava after it reaches the surface  

iv) Volcanoes allow for outgassing  

c) Tectonics

i) Disruption of a planet’s surface by internal stresses

ii) Convection of the mantle creates stresses in the crust called tectonic forces  iii) Compression of the crust creates mountain ranges  

iv) Valley can form where crust is pulled apart  

v) Lithosphere is fractured into more than a dozen plates  

d) Erosion

i) Surface changes made by wind, water, or ice

ii) All dependent on the presence of an atmosphere  

e) Last 3 processes stop once the internal heat is gone***

9) During volcanic eruptions, copious amount of gas is released ???? outgassing ???? replenishes  gas in atmospheres

a) This is where most terrestrial planets got their atmospheres***

b) Atmospheres diffuse away if not continuously replenished  

10) Earth’s atmosphere creates erosion, protects from radiation, responsible for greenhouse  effect, makes sky blue

a) Atmosphere created by outgassing from volcanoes  

b) About 10 km thick

c) Consists of mostly nitrogen 77%, oxygen 21%, Argon 1%

d) Why the sky is blue

i) Atmosphere scatters blue light from the sun more than red light  

11) Greenhouse gases (CO2, H2O, CH4) trap in infrared photons emitted by blackbody Earth ???? make surface warmer

12) Moon and Mercury had geological activity (~3 billion years ago) – maria on Moon –  but  not any longer (too small, lost internal heat) – no atmospheres because no more  outgassing  

a) Lunar maria:  

i) Some volcanic activity 3-3.5 billion years ago must have flooded lunar craters,  creating lunar maria  

ii) Maria have few crater that formed after the period of heavy bombardment  b) Mercury has a mixture of heavily cratered (oldest) and smooth regions (somewhat  younger) like the Moon.

i) The smooth regions are likely ancient lava flows.

ii) Long cliffs indicate Mercury shrank early in its history  

13) Mars – thin atmosphere, recent geological activity which is probably dying down now,  good evidence for much liquid water in past (know the evidence) ???? probably lost much of  its internal heat because of moderate/small size

a) Has dry ice polar ice caps that melt as summer approaches then condense at opposite  pole

b) If all ice melted an ocean 11 meters deep would form

c) Seasonal winds drive dust storms on Mars  

d) Had volcanoes as recently as 180 million years ago  

e) Past tectonic activity  

f) Water evidence  

i) Dried riverbeds???? 3 billion years’ old  

ii) Erosion of craters suggest they were once filled with swirling water  

iii) Impact craters show impact in ice and eroded craters from rainfall

iv) Rocks that form in water present ???? hematite “blueberries”  

v) Hydrated salts on slopes of Mars???? liquid water must have been flowing  g) Climate change on Mars  

i) Mars has not had widespread surface water for 3 billion years, but most likely had  water before that.

ii) Greenhouse effect probably kept the surface warmer before that  ???? lots of liquid  water? (extremely likely).

iii) Because of its smallish size, Mars lost most of its atmosphere

(1) low mass of Mars allowed gases to diffuse away from atmosphere.

(2) little/no additional gas replenishment from outgassing once volcanism  diminished

14) Venus – extremely thick atmosphere, very recent geological activity, greenhouse effect  run wild

a) Has impact craters but fewer than the moon, mercury or mars due to thick atmosphere  b) Has many volcanoes with evidence of recent activity?

c) Copious sulfur dioxide indicates outgassing is ongoing  

d) Fractured and contorted surface indicates tectonic stresses in the past???? unclear of  tectonic activity today  

e) Very little erosion due too slow rotation and no wind  

f) Greenhouse effect on Venus keeps it so hot  

g) Runaway greenhouse effect: would account for why Venus has so little water and such a  high temperature  

15) Earth – broken lithosphere allows plates to drift ???? continents move slowly 16) Continental motion – caused by spreading of sea floor ???? hot rock pushes up from mantle  pushing plates apart

17) CO2 cycle keeps CO2 levels stable ???? good for climate stability on Earth 18) Fossil fuel burning is raising CO2 levels to unprecedented levels ???? can Earth’s CO2 cycle  compensate?

19) A planet’s chance to harbor life depends on its distance from the Sun (not too hot, not too  cold) and size (large enough to maintain internal heat for geological activity) ???? Lucky  Earth!

a) Location allows liquid water to exist

Chapter 8: 

1) Jupiter & Saturn – mostly H/He, Uranus/Neptune – mostly hydrogen compounds, all  contain some rock/metal

2) Jovians became large (compared to terrestrials) because their cores could collect ice in  addition to rock/metal

a) Hydrogen compounds were more abundant then rock/ metal so Proto-Jovian planets  got more massive and acquired H/He atmospheres  

b) No solid surface  

c) Layers under high pressure and temperatures  

3) All Jovians have ice/rock/metal cores of ~5-10 Earth masses. Jupiter/Saturn also accreted  a lot more H/He because they formed first in denser part of solar nebula a) More H/He in Jupiter and Saturn  

b) More ices (hydrogen compounds) in Uranus and Neptune  

c) Differences in Jovian Planet Formation  

i) TIMING: The planet that forms earliest captures the most hydrogen and helium gas.  Capture ceases after the solar wind blows the leftover gas away.

ii) LOCATION: The planet that forms in a denser part of the nebula forms its core first   ???? favors Jupiter, then Saturn, but disfavors Uranus, Neptune

4) Jupiter is denser than its H/He composition implies, because its outer layers compressed  the inner layers

a) Core is thought to be made of rock, metals and hydrogen compounds  b) Tremendous pressure within inner layers leads to extremely high temperatures i) Cause phase of hydrogen to change with depth  

ii) Hydrogen acts like a metal at great depths because its electrons more freely  (metallic hydrogen)

5) Cloud layers on Jupiter (and to lesser extent Saturn) due to reflection off different  molecules (NH3, H2O, NH4SH)

a) Ammonium hydrosulfide clouds (NH4SH) reflect red/brown.

b) Ammonia, the highest, coldest layer, reflects yellowish-white.

c) Hydrogen compounds in Jupiter form clouds (H/He are colorless).

d) Different cloud layers correspond to freezing points of different hydrogen compounds. e) Saturn’s layers are similar, but sunlight is reflected at a deeper depth. More absorption  of light on the way back out leads to more subdued colors.

6) Uranus & Neptune are blue-green because of high concentrations of methane in their  atmosphere

a) Methane gas (20x more abundant by percentage than on Jupiter/Saturn) of Neptune  and Uranus absorbs red light but transmits blue light.

b) Blue light reflects off methane clouds, making those planets look blue. 7) All jovians have strong storms and strong magnetic fields

a) Jupiter’s Great Red Spot  

i) Storm twice as wide as Earth  

ii) Has existed for 3 centuries  

b) All the Jovian planets have strong winds and storms (much stronger than Earth’s). c) All the Jovian planets have strong magnetic fields (much stronger than Earth’s) 8) Small moons  

a) no geological history

b) odd shaped orbits ???? probably all captured comets

c) potato shaped  

d) < 300 km  

9) Medium moons  

a) past geological activity  

b) big enough for self-gravity to make them spherical in shape  

c) 300-1500 km  

d) formed in orbit around Jovian planets (like solar nebula)

e) Mostly circular orbits in the same direction as planet rotation (except Triton)  10) Large moons  

a) ongoing geological activity

b) driven by:  

i) (1) tidal forces (tidal heating) from host planet  

ii) (2) ice melts at much lower temperatures than rock

c) >1500 km  

d) formed in orbit around Jovian planets (like solar nebula)  

e) Mostly circular orbits in the same direction as planet rotation (except Triton)  11) Io (Jupiter moon) – most geologically active object in Solar System

a) Only Jovian moon made entirely of rock/ metal

b) Most volcanically active body in the solar system  

c) No impact craters at all  

d) Tidal Heating:

i) Io is squished and stretched as it orbits Jupiter from tidal forces (recall minor effect  of Moon on Earth’s tides).

ii) Elliptical orbit makes squishing more extreme.

iii) This extreme squishing heats the internal material and keeps it warm without  radioactive decay ???? so not geologically dead!

12) Europa (Jupiter moon) – liquid water ocean

a) Weaker tidal heating than Io (but still rather strong), small number of impact craters ???? surface no more than few tens of millions of years’ old  

b) Water is agent of change on surface of Europa (not rock as on Io).

c) Two choices:  

i) (1) liquid water    

ii) (2) warm ice that convects from the interior

d) Liquid water?

i) Europa’s magnetic field responds to Jupiter’s rotating magnetic field ???? models show  this should only happen if Europa has a liquid, charged layer in its interior.

ii) Salty compounds on surface of Europa ???? deposited by saltwater?

iii) If so, then Europa has 2x the amount of liquid water that Earth has (but all beneath a  frozen icy crust)!

iv) Europa is most likely place to harbor life (other than Earth, and possibly Mars). 13) Titan (Saturn moon) – thick atmosphere, liquid methane lakes

a) Atmosphere:  

i) Titan is the only moon in the solar system to have a thick atmosphere. ii) It consists mostly of 90% nitrogen with some argon, methane, and ethane (smoggy). iii) Erosion from liquid methane

iv) Liquid methane:  

(1) Rocks made of ice and liquid methane found by Huygens probe  

(2) Radar imaging shows dark, smooth regions that may be lakes of liquid methane  b) Saturn’s Moons

i) Almost call moons show evidence of past volcanism and or tectonics due to tidal  forces from Saturn  

ii) Mimas hit by large object  

iii) Medium Moons of Saturn  

(1) Enceladus’ ice fountains suggest it may have a subsurface ocean  

(a) Few impact craters  

(b) Tidal heating responsible for geological activity  

14) Saturn’s rings – consist of countless small bits of ice, not solid rings, ring system as thin as  length of Gallalee Hall

a) made up of numerous, tiny individual particles grain to boulder-size (not a solid disk) – each particle can be thought of as a tiny “moonlet” of Saturn.

b) ring particles orbit around Saturn’s equator.

c) ring system is very thin.

d) Chunks made of water ice and 10 meters in size and smaller  

15) All Jovians have ring systems – small particles must be constantly replenished from  impacts on moons

a) All four Jovian planets have ring systems in equatorial plane.

b) Others have smaller, darker ring particles than Saturn, sometimes made of dust. c) Ring formation

i) Jovian rings formed from ongoing impacts on moons orbiting those planets  depositing dust/ice into orbit.

16) Saturn’s spectacular ring system is probably transitory (ice moon broke apart) and it will  have a normal Jovian ring system in 1 billion years as particles grind down a) Saturn’s incredible rings may be an “accident” of our time – small icy moon broken apart  

rather recently led to boulder sized objects in rings  ???? all boulders will be ground down  to ice dust in a billion years or so and it will have a more modest ring system like the  other Jovians.

Chapter 9: 

1) Asteroids: leftovers from early Solar System, >500,000 now cataloged; adding up all  asteroids wouldn’t even give you a large moon. They are not the remnants of a large  terrestrial planet that exploded.

a) Small asteroids are more common than large asteroids  

b) Asteroids are cratered and not round (except Ceres)  

c) The largest is Ceres  

i) Only Ceres is large enough to be spherical ???? self-gravity

ii) First to be discovered  

iii) Only dwarf planet in asteroid belt  

d) Brightest asteroid is Vesta  

e) Some larger asteroids have moons  

2) Asteroid belt located between orbits of Mars and Jupiter, but still inside the frost line. a) Asteroids are very far away from each other???? almost impossible to get hit if you were  to fly through the asteroid belt  

3) Meteoroid/meteor/meteorite – know the difference

a) Meteoroid: a sand- to boulder-size piece of asteroid or comet (or planet) floating  through interplanetary space in Earth’s vicinity

b) Meteor: the bright trail in the sky left by a meteoroid (also called a “shooting star”) as it  burns up in the atmosphere

c) Meteorite: a rock from space that falls through Earth’s atmosphere and lands 4) Primitive (chondrite) meteorites  

a) oldest (4.6 billion years)

b) unprocessed, just as they were when they formed out of the solar nebula c) mixed jumble of rock and metal

d) Stony-iron mix (inner asteroid belt)

e) Carbon-rich mix (outer asteroid belt)

5) Processed meteorites  

a) either pure rock or pure metal

b) slightly younger than primitive meteorites

c) from asteroids that differentiated or had volcanic activity

d) pure metal-rich (cores of asteroids)  

e) purely rock (crusts of asteroids)  

6) Comets are the icy analogs of asteroids, and formed outside the frost line a) most comets do not have tails  

b) most comets remain perpetually frozen in the outer solar system  

c) only the very few comets that enter the inner solar system grow tails*** 7) Comet nucleus – “dirty snowball”, only the small fraction of comets (those that happen  to go near the Sun) sport long tails

a) contain hydrogen compounds and complex organic compounds

b) source of material for comets tail

8) Ice/hydrogen compounds melt when near Sun to give the comet an atmosphere (“coma”)  and plasma/dust tails

a) A coma is the atmosphere that comes from a comet’s heated nucleus.

b) A plasma tail is gas escaping from coma, pushed by the solar wind (protons and  electrons)

c) A dust tail is pushed by photons (light) from Sun

d) Tails can be hundreds of millions of km long (i.e. more than 1 AU)

e) Tails always point away from the Sun****

9) Comet debris (sand grain size) littered along orbit cause meteor showers when the Earth  crosses though this debris

10) Short-period comets – from Kuiper belt (30-100 AU from Sun) ???? nice (mostly) orderly  orbits in thin plane  

11) Long-period comets – from (unobserved) Oort cloud (~1 light year from Sun) ???? random,  3d orbits – flung out there by Jupiter?

12) Pluto, Eris, other large Kuiper belt objects look more like large icy comets than  terrestrial/Jovian planets ???? dwarf planets

a) Pluto has more in common with comets than with the eight major planets b) 12 other icy objects like Pluto discovered  

c) all classified as dwarf planets

d) to be a planet, an object must satisfy these 3 rules  

i) is in orbit around the Sun (not another object)

ii) has sufficient mass to be spherical

iii) has “cleared its neighborhood” of other objects

13) Comets/asteroids hit Jupiter (and Earth), sometimes with devastating effects ???? most  likely killed dinosaurs 65 million years ago (iridium/chromium layer in Earth’s rock  structure).

Chapter 10:  

1) Extrasolar planet detection (>3600 found so far): direct (actually see planet) vs. indirect  (astrometric (not effective yet), Doppler, transit) – know basic technique and biases of  each method

a) Direct: images or spectra of the planets themselves (reflected starlight)  ???? very difficult,  but accomplished very recently

b) Indirect: measurements of changes in star’s properties as a result of the planet ???? came  first, most common

(1) Astrometric Technique  

(a) In principle, we should be able to detect planets by measuring the change in  a star’s position on sky.

(b) However, these tiny motions are very difficult to measure.

(c) NOT an effective means of detecting planets with current technology (no  planets discovered this way so far – but soon!)

(2) Doppler Technique  

(a) Measuring a star’s Doppler shift can tell us its motion toward and away from  us as a result of a gravitational tug by an orbiting planet.

(b) When star is moving toward us (in its orbit about its center of mass) its light  is blue shifted; when moving away its light is redshifted.

(c) Current techniques can measure motions as small as 1 m/s (walking speed!). (3) Transit Technique  

(a) A transit is when a planet crosses in front of a star.

(b) The resulting eclipse reduces the star’s apparent brightness slightly and tells  us the planet’s radius.

(c) Only works if system is seen edge-on! ***

c) Gravitational tugs

i) The Sun and Jupiter orbit around their common center of mass.

ii) The Sun therefore wobbles around that center of mass with same period as Jupiter. 2) Hot Jupiters and very elliptical orbits provide challenge to solar nebula theory a) Some massive planets, called Hot Jupiters, orbit very close (< 0.1 AU) to their stars  (Mercury orbits Sun at 0.39 AU).

b) Some extrasolar planets have highly elliptical orbits (Recall: 8 planets in our own Solar  System have nearly circular orbits).

3) Planetary migration (pushing planets formed outside the frost line closer to the star) or  gravitational encounters (sending a planet into a highly elliptical orbit) can reconcile Hot  Jupiters/highly elliptical orbits with solar nebula theory

a) Nebular theory  

i) The nebular theory predicts that massive Jupiter-like planets should not form inside  the frost line (inside ~3.5 AU).

ii) The discovery of Hot Jupiters and highly elliptical planetary orbits has forced  reexamination of the nebular theory.

iii) Planetary migration and gravitational encounters may explain “Hot Jupiters” and  oddly elliptical orbits.

b) Planetary Migration

i) A young planet’s motion can create waves in a planet-forming disk.

ii) Models show that gravity of matter in these waves can tug on a planet, causing its  orbit to migrate inward inside the frost line (although this did not happen in our  Solar System).

c) Gravitational Encounters  

i) Close gravitational encounters between two massive planets can eject one planet  while flinging the other into a highly elliptical orbit.

ii) Multiple close encounters with smaller planetesimals can also cause inward  migration.

Clicker Questions:  

1) Which of the following is not a common characteristic of the terrestrial planets? a) Answer: They have similar chemical composition as the Sun  

2) Clicker Question: How do gas giant (Jovian planets differ from the terrestrial (rocky/ metal)  planets?

a) Answer: gas giants have many moons, gas giants are made mostly of H/He and hydrogen  compounds, gas giants have rings  

3) Clicker Question: Which of the following pairs of objects are primarily rocky objects? a) Answer: Terrestrial planets and asteroids

4) How would the Solar System be different if the solar nebula had cooled with a temperature  half its actual value at every distance  

a) Jovian planets would have formed closer to the Sun  

5) Which materials can be found in Jovian planets even in modest quantities? a) Hydrogen, helium, hydrogen compounds, rock, metal  

6) What key quality is responsible for the Moon and Mercury being geologically dead? a) Their size  

7) Which of the following is the only process capable of shaping the surface of a dead world? a) Impact cratering  

8) Which of the following is not evidence that liquid water existed on the surface of Mars in  the distant past?

a) Fossilized Coral Reefs  

9) Ultimately, why doesn’t Mercury have a very thick CO2 atmosphere like Venus? a) Mercury is much smaller than Venus  

10) All the Jovian’s share the following properties except:

a) A mostly H/He composition  

11) What does the lack of craters on Io tell us?

a) Io’s surface must be very young

12) Which of the following is not an explanation for why icy moons can still have geological  activity while small terrestrial planets do not?

a) Icy moons were formed with more radioactive material than small terrestrial planets  13) Which of the following is true about ring systems and Jovian planets? a) All Jovian planets have a ring system  

14) Why are asteroids rocky or metallic?

a) There was no ice in the part of the Solar System where they formed  15) Which of the following is not evidence that an asteroid impact killed the dinosaurs? a) The period of heavy Bombardment occurred at the time the dinosaurs died  16) Which of the following is false about extrasolar planets and their detection? a) So far, all other solar systems look just like our Solar System

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