Solar System Physics Flashcards

1
Q

What does the solar system consist of?

A

the Sun orbited by the 8 planets (4 terrestrial, 4 jovian), minor bodies
including dwarf planets (e.g. Pluto), asteroids, comets, and other debris left over from the formation of
the solar system.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

planet

A

in orbit around a star, and is massive enough to be spherical
(or nearly spherical!) and to have cleared its own orbit of other objects.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

2 groups of planets in the solar system

A

terrestrial and jovian
each has very distinct properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is gravity responsible for?

A

orbits of planets around the Sun, and moons/satellites around planets.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Gravitational potential energy released by matter falling towards a gravitating object…

A

is converted to kinetic energy, which can in turn be converted to other forms (e.g. heat).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

surface gravity

A

Surface gravity is the gravitational acceleration (force per unit mass) at a planetary surface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

tidal force

A

The tidal force is the difference in gravitational force experienced by 2 parts of an object.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

If a planetary atmosphere is hotter than the escape temperature for a given atom or molecule…

A

then that atom or molecule is not present in the atmosphere.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When is the escape temperature higher?

A

for more massive planets (stronger gravitational acceleration)
and for heavier atoms/molecules (need more energy to go fast enough to escape).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Scale height

A

Atmospheric pressure decreases exponentially with increasing height. The rate at which it
decreases is given by the scale height.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

If the atmospheric temperature increases…

A

the scale height increases, and the atmosphere extends further out from the planet or star.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Jovian planets are primarily composed of…

A

Hydrogen and Helium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

outer layers of jovian planets

A

Are gaseous, therefore rotate differentially (not all latitudes have the same angular speed) and are slightly oblate due to the centrifugal force being stronger at their equators.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

outer layers of Jupiter and Saturn

A

The gaseous outer layers of Jupiter and Saturn display complex flows (zones and belts, storms,
vortex structure).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Jovian planets core

A

Jovian planets have cores composed of dense ‘soups’ of rock and ices, or rock alone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

strong magnetic field in Jupiter and Saturn

A

Liquid metallic hydrogen in Jupiter’s and Saturn’s interiors produces a strong magnetic field.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Weak magnetic fields in Uranus and Neptune

A

Ionic ‘oceans’ in Uranus and Neptune produce weaker magnetic fields.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

how are the interiors of jovian planets heated

A

heated by the gravitational potential energy released as heavier elements sink slowly towards the core.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why are rings thin?

A

Rings are thin because inelastic collisions in the vertical direction remove energy and linear
momentum from the colliding particles, while angular momentum is conserved.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Roche stability limit

A

Within a critical radius, known as the Roche stability limit, an object will be pulled apart by tidal
forces. Saturn’s rings lie mostly inside this radius.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What do tidal forces acting on moons cause?

A

frictional heating of the moons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what can tidal friction on a planet do?

A

slow down its rotation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Because angular momentum of planet and moon must be conserved,

A

this means the planet speeds up, so its orbital radius increases.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

The inner 2 Galilean moons

A

rocky
show more evidence of volcanic or tectonic activity, and less evidence
of impact cratering

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
The outer 2 Galilean moons
rock/ice
26
layers of the sun
The Sun can be divided into 3 interior layers (core, radiative zone, convective zone) and 3 outer atmospheric layers (photosphere, chromosphere, corona).
27
what happens in the suns core?
In the core, nuclear fusion of H to He is taking place, providing the Sun’s energy.
28
Radiative zone in the sun
In the radiative zone energy is transported by photons which scatter very frequently and distribute energy through the interior.
29
Convection zone of the sun
In the convective zone energy is transported by rising and falling flows of gas.
30
The visible solar surface (photosphere)
approximately a blackbody radiator, obeying the StefanBoltzmann Law and Wien’s Displacement Law.
31
Temperature in sun
The temperature decreases from the core to the photosphere, then increases from photosphere into chromosphere and corona. It is not known how this increase happens.
32
The solar atmosphere
permeated by a strong magnetic field which is generated in its interior by a dynamo, and emerges at sunspots.
33
Solar magnetic field
imposes complicated structures on the solar atmosphere and is responsible for solar activity, which varies on an approximately 11-year cycle.
34
Solar wind
The solar wind is a constant stream of hot gas from the Sun’s surface.
35
structure of terrestrial planets
The terrestrial planets have a metallic core (formed by gravitational differentiation), a rocky mantle and a thin crust.
36
Earth's magnetic field
Earth’s magnetic field implies a liquid core and a dynamo.
37
Mercury's magnetic field
weak
38
Mars and Venus magnetic field
neither Mars nor Venus shows evidence of a current planetary dynamo.
39
Atmospheres of Venus and Mars
predominantly CO2 and N2
40
Venus atmosphere
very high pressure
41
Mars' atmosphere
very low pressure
42
what makes Earth's atmosphere special?
The Earth is the only planet with substantial O2, which is generated by plant life.
43
Surfaces of terrestrial planets
The surfaces of the terrestrial planets have been shaped by impact cratering, volcanism, tectonic activity and erosion.
44
surface of Mercury and the moon
substantial evidence of impact cratering but no recent volcanic or tectonic activity, or erosion.
45
surface of Venus
Venus is thought to still be very volcanically active.
46
surface of Mars
Mars shows evidence of weathering by wind and flowing water in the past.
47
How to find radius and mass of the Earth
The radius and mass of the Earth can be obtained from astronomical measurements
48
interior structure of the Earth
deduced by seismology using pressure (P) and shear (S) waves.
49
what does the seismic shadow for shear waves provide evidence for?
a liquid core
50
How can the age of the Earth be obtained?
The age of the Earth (and other solar system objects) can be obtained by radioactive dating using long-lived radioisotopes. It is ~4.5 billion years old.
51
3 ways a planet can be heated
1. accretionary heating 2. radiogenic heating 3. solar heating
52
accretionary heating: what is the energy loss?
as mass falls towards protoplanet, loses potential energy. Ulost=Ur-UR if from great distance r>>R so Ulost=GMm/R
53
initial temperature of Earth: considering mass of dust falling towards early Earth
loses PE as it falls, gains KE. Suppose contains N atoms, average mass per atom m. N=M/m KE converted to thermal energy E=3.2kbT so Etot=3/2NkbT=3/2kbTM/m
54
how hot was newly formed Earth?
from energy conservation: GMm/R=3/2kbTM/m T=2/3 GmM/kbR if assume accreting material is silicon, T=8*10^4K
55
cooling of Earth
temp changes, luminosity (energy loss rate) changes differential equation gives cooling time of 8*10^4 years to cool to 300K
56
what does radioactive decay of elements inside Earth release?
heat energy
57
how to estimate how much power is produced by radiogenic heating?
1. consider reaction and associated half life 2. work out fraction of total mass converted to energy 3. energy released per kg by knowing how much of an atom in 1kg of Earth. 4. power per kg=energy per kg/half life 5. x by M earth
58
what does radiogenic heating cause?
it may drive convection currents in the mantle, carrying energy from the deep interior to the Earth's surface.
59
Albedo
much of the flux reflected back into space and not contributing to heating (albedo). A=sunlight reflected/sunlight received
60
solar power receveid by planet
cross-sectional area times the flux power reflected= AP power absorbed=(1-A)P
61
power radiated by a planet: what assumption is made?
planet radiates like a blackbody
62
power radiated by planet: over long timescale what will happen?
planet will come into equilibrium such that power in=power out
63
temperature of planet due to solar heating derivation
equate pin and pout for expression for Tp substitute for F combine together
64
assumptions made for temperature of a planet due to solar radiation:
1. temperature and the albedo are the same everywhere on the planet 2. the planet behaves like a perfect blackbody 3. all latitudes receive an equal amount of incoming solar radiation
65
why when comparing theoretical and observed temperatures of planets, do venus and earth have far higher observed temps?
greenhouse effect (jupiter to neptune slightly higher but due to internal heating)
66
greenhouse effect on Earth
atmosphere transparent to visible light. solar radiation heats surface, re-radiates at infrared wavelengths atmosphere not transparent at infrared wavelengths so IR absorbed this heats up atmosphere and it re-radiates IR, heating up surface.
67
why is the greenhouse effect on Venus runaway?
venus closer to sun, water exists as water vapour, trapping IR. Scale height for H20 increases, UV and X-rays dissociate water molecules. Without water, atmosphere is mainly CO2
68
definition of planet
orbits sun massive enough to be spherical has cleared its orbit of debris
69
definition of dwarf planet
orbiting sun massive enough to be spherical has not cleared its orbit of planetesimals
70
definition of minor planet (includes asteroids)
orbiting sun but not massive enough to be spherical and orbit not cleared
71
definition of trans-neptunian object (Kuiper Belt objects)
dwarf/minor planet orbiting sun at a greater average distance than Neptune
72
largest and most massive asteroids in the asteroid belt?
Ceres, Vesta and Pallas
73
what is the structure in the asteroid belt (kirkwood gaps) due to?
orbital resonances with Jupiter asteroids line up with jupiter and receive gravitational tugs that deflect them into new orbit (empty locations)
74
two theories for the origin of the asteroid belt
1. debris left over from the break-up of a planet 2. primordial rocks that never managed to accrete to form a planet
75
which theory favoured for origin of asteroid belt?
primordial rocks not enough mass to make up a moon differences in chemical composition of asteroids shows they don't have a common origin gravity of jupiter would prevent asteroids accreting into a more massive body
76
how to we learn about asteroids?
some visited by spacecraft but also learn a lot from meteorites (asteroid fragments that survive impact with the Earth
77
what does the chemical composition of an asteroid tell us?
their age chemical composition can be determined from spectra, observations from Earth or by spacecraft
78
3 main asteroid groups
Carbonaceous (C-type) Silicate (S-type) Metal (M-type)
79
carbonaceous asteroids
about 75% of population primordial (unchanged) darkest, least reflective, contain primarily carbon dominate outer parts of asteroid belt
80
silicate asteroids
about 17% of population undergone significant melting and reformation younger than C-type brighter (stony, mineral composition) dominate inner parts of belt
81
metal asteroids
around 8% of population cores of progenitor bodies, disrupted through collisions consist primarily of iron and nickel.
82
what are the trojans?
two groups of asteroids orbiting about 60 degrees ahead and behind jupiter
83
The trojans are grouped around lagrange points L4 and L5. What are these?
where the gravitational forces from jupiter and the sun balance the centripetal force due to orbital motion
84
what are comets?
"dirty snowballs" rocky/icy objects orbiting sun on highly eccentric elliptical paths
85
why do comets contain large amounts of ice?
spend most of their lives very far from the Sun (Kepler 2) so contain large amounts of ice as one nears the sun, it produces a coma and tail (outgassing)
86
structure of a comet
coma - atmosphere of gas and dust, surrounds the nucleus. ion tail - ionised gas from coma pushed away from sun by solar wind dust tail - follows curved path due to outward force exerted by Sun's radiation pressure on dust particles
87
comet tails around the sun
tails get longer the closer a comet gets to the sun as approaches sun, tails stream behind it but after passing perihelion the comet tails will stream in front of the coma and nucleus.
88
short period comets
period less than 200 years aphelion outside the orbit of neptune, originating in the Kuiper belt eg: Halley's comet, T=76y
89
long period comets
10^4-10^7 years originate in the oort cloud
90
oort cloud
a spherical cloud of debris from the formation of the solar system extending to around light year contains 10^12-10^13 comets with a total mass of a few hundred Earth masses
91
meteoroid
the object itself, originally part of a comet or asteroid
92
meteor
visible streak of light in the sky produced when a meteor enters the Earth's atmosphere
93
meteorite
remains of the meteoroid if it reaches the Earth's surface intact
94
meteor shower
rate of around 1000 meteors an hour, tend to come from a particular direction - radiant point. occurs when the Earth [asses through a trail of debris behind a comet (usual rate around 20 an hour)
95
interaction of meteoroid with the atmosphere
KE and momentum of a meteoroid reduced by air friction as it enters atmosphere heating and mass loss leaves a glowing tail meteorite surfaces are blackened and fused due to high temperatures created as they pass through atmosphere.
96
meteorite classification: 4 possibilities
chondrite (86%) achondrite (8%) iron (5%) mixture (1%)
97
chondrite meteorite
primordial from outer belt
98
achondrite meteorites
from molten rock in crusts or other asteroids, moon or mars ejected into space due to impacts with parent body
99
iron meteorites
iron-nickel composition implies origin in the cores of asteroids
100
mixture meteorites
stony-iron composition outer cores of asteroids?
101
kinetic energy of a meteoroid
considering cubical meteoroid of side d, density p and speed v. Ek=1/2pd^3v^2
102
stopping height of a meteoroid
air resistance slows meteoroid down as encounters Earth's atmosphere assume will stop when encounters mair = its own mass mair=volume of air encounteredxdensity set m meteroid = m air
103
luminosity of a meteoroid
estimate from energy loss during deceleration power dissipated=energy/time sub in stopping time=H/v most observations come from height<30k so can use to estimate radiation flux at Earth assuming 10% of power dissipated emerges as light.
104
comparison of the rotational angular momentum of the sun with the orbital angular momentum of Jupiter
L=RMV=RMwR where w=2pi/T for sun gives: 2.8x10^42 kgm^2s^-1 for jupiter: 1.6x10^43 kgm^2s^-1 Jupiter more than 6 times larger than sun. Did sun transfer angular momentum to planets?
105
The Nebular Hypothesis
everything is solar system formed from a large cloud of interstellar gas and dust which collapsed under its own gravity *evidence of such disks in other systems that are still forming*
106
Timeline - first 100,000 years
nebula becomes gravitationally unstable and starts to collapse central region heats up forming protostar rotation speeds up as material falls inwards and cloud flattens to disk
107
Timeline - 100,000 to 10 million years
nebula exists with protostar surrounded by proto-planetary disk protostar becomes a T Tauri star, heated by gravitational contraction further out material accretes to form planetesimals beyonf 4 or 5 au, icy planetesimals can form (jovian planets)
108
why would the jovian planets need to form within 10 million years?
still enough gas to build them up
109
how do terrestrial planet form?
through accretion of multiple planetesimals into a more massive body. (takes 10-100 million years for Earth sized object to form within approx 3 au)
110
Timeline - 10 million to 0.1 billion years
solar system consists of protoplanets and planetesimals orbiting proto-sun, nebular gas has mostly dissipated large impacts during this time (explains Venus, Earth-Moon system etc.)
111
Timeline - >0.1 billion years
temp and pressure in core of proto-sun high enough for nuclear fusion asteroid belt and Kuiper belt form as other planetesimals cleared period of late heavy bombardment Jovian planets migrated to current orbits?
112
Timeline - 1 billion years
end of heavy bombardment and migration first simple life on Earth (Australia fossils)
113
Problems with Solar System formation timeline
1. not enough gas in protoplanetary disk to let Jupiter and Saturn reach their current masses if they formed in current orbits 2. cannot fully explain all impact craters on terrestrial objects created during heavy bombardment 3. absence of super-Earths in the inner Solar system compared to exoplanet observations
114
what would resolve problems with Solar System formation timeline?
if Jupiter and Saturn formed closer to Sun, first migrated inwards, then outwards (gravity would prevent massive rocky planets forming)
115
three main methods to detect extrasolar planets
1. radial velocity 2. transit method 3. direct detection. 1. and 2. use the effect of the planet on its star
116
radial velocity method
for massive stars, wobble (due to orbit of centre of mass) can be detected by doppler shift of spectral lines emitted by star
117
Transit method
stars light intensity decreases when the planet passes between the star and our line of sight
118
Direct imaging method
light from star removed by components in telescope that destructively interfere with starlight light from planet unaffected and computer processing used to detect planet works best infrared and for planets far from their star