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astro 4 Flashcards

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1
Q

did the terrestrial planets all look quite similar last time

A

The surfaces of all 5 terrestrial worlds (Mercury, Venus, Earth,
Moon, Mars) must have looked quite similar when they were
young, and all were subjected early on to the Heavy Bombardment

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2
Q

How did the terrestrial inner worlds ended up so different although
they were made similarly from metal and rock that had condensed in
the initial solar nebula?

A

Their current appearances must be the result of changes that
occurred after their formation & initial ‘childhood’ (i.e. due to
their planetary evolution).

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3
Q

do all the terrestrial worlds have the same type of distinct

layering

A

g due to (at some time in the past) differentiation
= process where gravity separates materials by density -> ALL terrestrial planets must once have been hot enough for
the interior rocks & metal to melt
& separate by density

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4
Q

The interiors of any terrestrial planet is divided into 3 major layers

A

Core: made of the highest density materials (e.g. Ni, Fe)
Mantle: made of rocky material of moderate density
(minerals containing mainly Si, Mg, O)
Crust: made of rocky material of lowest density, e.g. granite
& basalt (volcanic rocks)

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5
Q

what is granite

A

Granite is a course-grained rock
composed mostly of quartz and solidifies
underground

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6
Q

what is basalt

A

Basalt is a fine-grained rock rich in Mg &
Fe exposed at or very near the surface of a
rocky planet or a moon. More than 90% of
all volcanic rock on Earth is basalt

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7
Q

which is denser & heavier, basalt or granite

A

Basalt

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8
Q

what is the rigid lithosphere

A

crust and part of mantle

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9
Q

what are the layers of earth in order

A

rocky crust>rigid lithosphere > mantle > metal core

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10
Q

The outermost rigid part of a planet is called

A

lithosphere

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11
Q

what generally encompasses the crust and part of the mantle

A

lithosphere

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12
Q

what is The upper layer of the mantle right below the lithosphere

A

asthenosphere

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13
Q

asthenosphere

A

It has relatively low resistance to plastic flow as it is hotter
and more fluid and this is where convection is thought to occur

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14
Q

what thickness is closely related to planetary size!

A

Lithospheric thickness

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15
Q

 Small worlds tend to have thicker

A

=lithospheres

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16
Q

Why are planets round?

A

Rocks deform & flow under high
p and/or T, and the gravitational field originating from the center acts
equally in all directions and pulls everything toward it, ultimately
smoothing out the shape into a sphere.

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17
Q

 The weak gravity of a small object is

A

s unable to overcome the rigidity of its

solid material clustered together

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18
Q

Within 1b y gravity will make into a sphere

A

any object bigger than ~500 km in diam.

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19
Q

Geological activity

A

the process of ongoing changes in the surface & structure of a planet

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20
Q

Why were the planets hot? What is/was the source of this energy?

A

3 sources of energy for the internal heat of terrestrial worlds:
 Heat of accretion
Differentiation
Radioactive decay (fission

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21
Q

Heat of accretion

A

Gravitational potential energy of a planetisimal is converted into kinetic energy
which, upon impact, is converted into heat

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22
Q

Differentiation

A

Release of additional heat as dense
materials sank to core and convert their
gravitational potential energy into heat

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23
Q

 Radioactive decay (fission)

A

Radioactive isotopes (U, Th, K) convert
their mass-energy (E=mc
2) into heat
 Declines in time —>much more significant
when planets are big and/or young
 Still
supplies heat to the terrestrial interiors but
at a lower level than when the planets were young.

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24
Q

How interiors cool off

A

convection, conduction, radiation

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25
e most important factor | in planetary cooling.
size
26
 Convection:
heat transported upward as hot material expands & rises, dissipates energy at the outermost surface, then cooler material contracts & falls  Occurs if the heating source is below
27
Conduction:
heat transfer from a hot material/region to a cooler one through contact  Due to microscopic collisions of their constituent particles (atoms/molecules)
28
Radiation:
Thermal radiation carries energy away from object  Planck’s law: ANY blackbody emits radiation characteristic of their temp. T  Because of their low T, planets emit in IR
29
Large planets retain
n internal heat much | longer than smaller ones!
30
Lithosphere grows thicker
as planet’s interior cools.
31
what is the primary driver of geological activity
Interior heat
32
most important heat transfer process of Earth
Convection thru convection cells within the mantle
33
Mantle convection primarily involves
solid rock(not molten rock)
34
how long does mantle convection take
is a very slow process (a few cm/year!, i.e. a full cycle takes ~500m y)
35
The mantle is made of solid rock because
after Earth’s formation it cooled over m of years. Water trapped inside minerals erupted with lava, a process called “outgassing--->the mantle solidified.
36
Mantle convection stops at
the base of lithosphere.
37
why does Mantle convection stop at the base of lithosphere.
Heat dissipates upwards primarily through conduction, then radiates away into space once it reach Earth’s surface  Primary driving force for the movement of the tectonic plates = the pieces into which the lithosphere is broken  Lava erupting from volcanoes comes only from a narrow region of partially molten material beneath the lithosphere.
38
Planetary size determines
the strength of mantle | convection & lithospheric thickness
39
Venus is probably similar to Earth in
n its internal | heat & nearly as geologically active as Earth.
40
what is the problem on venus lol
 Problem: lack of water, which on Earth (incorporated in many minerals, e.g. olivine) acts as lubricant and eases tectonic plate movements.
41
The Moon has a very thick lithosphere & no | geological activity due to
its small size
42
Mercury also cooled quickly but
may still retain some heat in its very large core.
43
Mars, intermediate in size, has cooled | significantly but
probably retains enough internal heat for some reduced geological activity.
44
Why do some planetary interiors create a magnetic field?
``` Interior heat plays another crucial role: it can create a global magnetic field (MF) → creates a magnetosphere. ```
45
3 basic requirements to generate a global magnetic field (MF):
 An interior region of electrically conducting fluid (gas/liquid, e.g. molten metal)  Convection in that layer of fluid  At least moderately rapid rotation around its axis.
46
 Earth = the only terrestrial world that meets ALL 3 BASIC requirements
Dynamo effect: Earth’s MF is due to | convection in the liquid outer core AND the Coriolis force due to Earth’s rotation
47
The Coriolis force tends to o
organize the flow within the outer core | into rolls aligned along the N-S polar axis.
48
None of the other terrestrial planets has
a MF as strong as Earth’s
49
 Electrons | (e–) in molten metal move within the outer core ________________
similar to the current flowing thru an electromagnet but in a self-sustaining process.
50
Why do some planetary interiors create a magnetic field? Moon:
core has long since cooled & stopped convecting  no MF
51
Why do some planetary interiors create a magnetic field? Mars
: Its core (part of mantle too??) probably still retains some heat, but not enough to drive core convection, hence it lacks a MF.
52
Why do some planetary interiors create a magnetic field? Venus
: probably has a molten core similar to Earth’s, but either its convection or very slow rotation is/are too weak to generate a MF
53
Why do some planetary interiors create a magnetic field? Mercury
an enigma as it does have a MF despite its small size & slow rotation → most probably due to a huge core that may still be partially molten and convecting.
54
Why do some planetary interiors create a magnetic field? Jupiter
has a very strong MF due to a layer of convecting metallic hydrogen & its rapid rotation.
55
Why do some planetary interiors create a magnetic field? Jupiter
At same planetary size, a molten metal layer generates a stronger MF than an ionic liquid
56
Why do some planetary interiors create a magnetic field?  Sun:
its MF is due to convection of ionized gas (plasma) & its | rotation.
57
A planet’s MF creates a
magnetosphere = a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field.
58
A magnetosphere acts as a
protective bubble which deflects | most of the charged particles in the solar wind
59
If the (Earth’s) magnetosphere were not present (or weak),
highly energetic particles can strip away atmospheric gases & cause genetic damage to living organisms.
60
ALL surface features on a terrestrial planet (e.g. on | Earth) are caused by just 4 major processes
Impact cratering: Volcanism: Tectonics: Erosion:
61
Impact cratering:
excavation of bowlshaped craters by asteroids or comets | crashing into the surface
62
Volcanism:
eruption of molten rock, or lava, from its interior onto its surface  Some planets may have instead cryovolcanism, in which volatiles/liquefied gases (e.g. H2O, NH3, CH4) are ejected instead of lava
63
Tectonics:
building/reshaping of surface features due to stretching, compression or other forces acting on the lithosphere
64
Erosion:
wearing down or building up of geological features by wind, water, ice & other planetary weather
65
Cratering
An impact crater forms when an asteroid/comet slams into a solid surface Many impact craters on Earth & other worlds, especially Moon & Mercury. Earth bombarded by impacts when it was young, but most ancient craters were erased by volcanic/geological activity & erosion  Craters can provide very important clues:
66
An impact crater forms when an | asteroid/comet slams into a solid surface.
 The released energy vaporizes rock and blasts out a crater = circular since material is ejected uniformly in all directions (for normal incidence!)
67
Many impact craters on Earth & other worlds, | especially Moon & Mercury.
 Most cratering happened soon after the Solar system formed (2 episodes of Heavy Bombardment).  Small craters far outnumber large ones  many more small objects than large ones in the initial solar nebula
68
 Craters can provide very important clues:
The more craters, the older the surface. |  The geological conditions existent at the time of impact
69
Volcanism
Volcanism occurs when underground molten rock (magma) finds a path to the surface through the lithosphere Volcanism produces volcanic mountains & explains the existence of our atmosphere & oceans.
70
Volcanism occurs when underground molten rock (magma) | finds a path to the surface through the lithosphere
``` Molten rock/magma = lower density  rises with respect to surrounding high density materials  The solid rock surrounding a magma chamber can squeeze it, driving it upward under pressure  Magma often contains trapped gases that expand as it rises  dramatic & violent explosive eruptions ```
71
 Volcanism produces volcanic mountains & explains the | existence of our atmosphere & oceans.
Water/ices originated from icy planetesimals, the rock from the asteroids & planetesimals whose merger made up the planet. The subsequent heavy bombardments may also have contributed significantly, especially with water/ice.  Volcanic eruptions release some of the initially incorporated gases/liquids (outgassing)  made Earth’s atmosphere & oceans.
72
Cryovolcanism: v
volcanism that may take place on cold worlds covered by ices (provided that an internal heat source is present). Molten rock/magma is called lava after it reaches the surface.  Lava can shape 3 different types of volcanic features, depending on its viscosity:
73
Lava can shape 3 different types of volcanic features, | depending on its viscosity:
Runny lava (i.e. with the lowest viscosity) makes flat lava plains.  Slightly thicker (i.e. more viscous) lava makes broad shield volcanoes.  The thickest (i.e. most viscous) lavas solidify very quickly and make steep stratovolcanoes
74
Tectonics
``` building/disruption of surface features by internal stresses caused (directly or indirectly) by convection in the underlying mantle. ```
75
Tectonics =
Compression forces where adjacent convection cells push rock together ---> mountain ranges  Cracks & valleys form where adjacent convection cells pull the crust apart
76
The stresses due to underlying mantle convection
fractured Earth’s | lithosphere into more than a dozen pieces called plates
77
plates
 Plates move over, under & around each other → plate tectonics
78
Only Earth has
plate tectonics
79
what generally occur together
Tectonics & volcanism generally occur together---> heat
80
Erosion
refers to weather-driven processes that break down or | transport rock through action of ice, liquid, or gas.
81
Erosion
Shaping of valleys by the flow of ice bodies (glaciers).  Carving of canyons by the flow of liquid water bodies (rivers).  Shifting of sand dunes by winds (gas).
82
Erosion can also
build up geological features  Sand dunes, river deltas, lake bed deposits, accumulation of sediments into layers on ocean floors -> sedimentary rocks.
83
Atmosphere
 In most cases it is a surprisingly thin layer (compared to the size of the world)  Can be a mixture of many different gases that may consist of individual atoms or of molecules.
84
The collisions of individual atoms/molecules in an atmosphere create pressure
 Ideal Gas Law equation: pV = NRT, where p & V = the pressure & the volume of the gas, N = the number of moles of gas, R = the universal gas constant, and T = the absolute temperature.  The gas in an atmosphere is held down by gravity.  The collision-resulting pressure acts uniformly, pushing in all directions, including upwards, making the atmosphere expand  Planetary atmospheres exist in balance between the downward weight of the gases & upward push of their gases.  p↓ with↑ altitude H→ because air density ρ↓: p=ρTR/M, with M = molar mass.
85
An atmosphere can have several key effects onto its planet:
 Its pressure (& temperature) determines if liquid (water) can exist on the surface.  Absorbs and scatters light.  Creates wind & weather.  Aurora is produced when the solar wind particles trapped in the magnetosphere make it through & collide with atoms/molecules in the atmosphere.  Can make planetary surfaces warmer via the greenhouse effect.
86
The greenhouse effect occurs only when
an atmosphere contains gases that can absorb IR light (e.g., H2O vapor, CO2, CH4) radiated back from the planet surface.
87
The energy of an absorbed IR photon is not retained for long but
re-emitted as another IR photon, which is again absorbed by another molecule, etc., etc.  greenhouse gases significantly slow down the escape of IR radiation from a lower atmosphere, while the molecular motions of the latter’s molecules heat it up (and also the planet’s surface)  The greenhouse effect does NOT alter a planet’s overall energy balance
88
Earth’s atmosphere consists of
77% N2, 21% O2 & small | amounts of other gases
89
 Earth’s atmosphere consists of 77% N2, 21% O2 & small | amounts of other gases.and what does that cause
 Enables presence of liquid water = explains extensive erosion on Earth  Sustains Life: without it, Earth’s surface would be lifeless due to the dangerous solar radiation & so cold that all water were frozen
90
 Earth’s atmosphere is
~480 km thick but ⅔ of our atmospheric air lies within 10 km of surface (90% below 16 km)!  Still other higher layers have vital roles (O 3 layer to block UV, absorption of X-rays)
91
Earth’s atmosphere has 5 basic | layers/regions:
Troposphere Stratosphere Mesosphere Thermosphere Exosphere
92
Troposphere =
= the lowest layer; here T↓ with↑ altitude H;
93
Stratosphere=
composed of stratified temperature layers; it begins where T↑ with↑H, due to UV absorption by ozone (O3);
94
Mesosphere =
= the region where T↓ again with↑ altitude H:  The stratosphere and the mesosphere are sometimes collectively referred to as the "middle atmosphere"
95
Thermosphere =
= begins where T again↑ with↑ altitude H;
96
Exosphere =
the uppermost region where the atmosphere gradually fades into space. The layering is shaped by the way each region interacts with various wavelengths of light
97
Exosphere
 Heated by solar UV & X-rays  Fast-moving gas molecules can escape to space
98
 Thermosphere
 X-rays heat & ionize gases
99
 Ionosphere
``` Made of ions created by energetic particles from solar wind and outer space  Reflects radio waves and solar wind  Comprises 4 layers (D, E, F1, F2) ```
100
Stratosphere
Heated by UV, layered, no convection
101
Troposphere
Greenhouse gases trap IR radiation from the ground  Convection important

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