Solar Systems Physics

Question 1

What does our solar system consist of?

Answer 1

The Sun, it’s eight planets and their moons, minor bodies (e.g. dwarf planets, asteroids, comets) and the “solar wind”.

Question 2

What did the geocentric (Ptolemaic) universe propose?

Answer 2

Plato proposed a geocentric universe, this means that celestial bodies followed a uniform speed in a circular motion, with earth at it’s centre.

Question 3

What does the heliocentric (Copernican) universe propose?

Answer 3

Nicolous Copernicus proposed a heliocentric universe, this model of planetary motion has the sun at the centre of our solar system, with the celestial bodies orbiting it.

Question 4

What is retrograde motion?

Answer 4

Retrograde motion is when a planet appears to move backwards, reversing it’s direction before resuming it’s original path. Mars is an example of a planet that undergoes retrograde motion.

Question 5

How can retrograde motion be explained in the heliocentric universe?

Answer 5

Retrograde motion can be explained by the earth “overtaking on the inside”

Question 6

How did Galileo’s observations support a heliocentric universe?

Answer 6

In 1610 Galileo’s observations of the moons of Jupiter and the phases of Venus supported the heliocentric universe. The Gibbous phase of the moon can only be explained within the heliocentric model.

Question 7

The orbits of the planets are _______?

Answer 7

Ellipses

Question 8

What is the ecliptic plane?

Answer 8

The plane of the Earth’s orbit around the sun, the planets lie in, or are close to the ecliptic plane.

Question 9

The mean distance from the earth to the sun is __________?

Answer 9

1au (astronomical unit)

Question 10

The surface temperature of the sun is __________?

Answer 10

5800K

Question 11

The central temperature of the sun is __________?

Answer 11

Approximately 15 million K

Question 12

The sun is a star, a ball made from mainly _____ and ______ gas.

Answer 12

Hydrogen and Helium

Question 13

How does the sun generate hear and light?

Answer 13

Nuclear fusion at it’s core

Question 14

What is hydrostatic equilibrium?

Answer 14

The balance maintained between pressure and gravity.

Question 15

The Suns outer atmosphere is known as the ______.

Answer 15

Corona

Question 16

The corona of the sun is heated by ______.

Answer 16

Twisting of the Sun’s magnetic field.

Question 17

Name the terrestrial planets:

Answer 17

Mercury, Venus, Earth and Mars. Terrestrial planets are the inner planets and are small and rocky.

Question 18

Name the jovian planets:

Answer 18

Jupiter, Saturn, Uranus and Neptune. Jovian planets are the outer planets and are gas giants.

Question 19

Explain the Giant Impact Hypothesis.

Answer 19

The Giant Impact Hypothesis is the generally accepted theory for the formation of the moon. It theorises that the moon was created from debris resulting from a collision with a Mars-sized object.

Question 20

What is the asteroid belt made out of?

Answer 20

Remnants of the material that used to reside between Mars and Jupiter, the belt is composed of remnants as small as pebbles and as large as approximately 560 miles. Jupiter’s gravitational field prevented formation of a larger object.

Question 21

Define a planet

Answer 21

It is 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

Question 22

How are asteroids and comets different?

Answer 22

The difference between an asteroid and a comet is primarily in its location in the solar system with asteroids being found in the asteroid belt between the orbits of Mars and Jupiter and comets spending most of their time in the outer reaches of the solar system

Question 23

How does the number of moons for the terrestrial planets compare with that of the Jovian planets?

Answer 23

Terrestrial planets have few or no moons while the Jovian planets have many

Question 24

What does Newton’s Law of Gravitation explain?

Answer 24

It explains gravity as a force of attraction between all matter in the universe.

Question 25

Why do different bodies have different gravitational fields?

Answer 25

The magnitude of a body's gravitational force is represented by the gravitational force per unit mass. Thus, different bodies, with different masses, should have different gravitational fields.

Question 26

Gravitational field can also be defined as _________.

Answer 26

Gravitational acceleration (F = ma)

Question 27

Explain gravity

Answer 27

Gravity is described as an inverse square law, i.e. the gravitational force between two bodies is inversely proportional to the square of their separation.

Question 28

How do you calculate the acceleration due to gravity on a spherically symmetric planet's surface?

Answer 28

By equating Newton's second law of motion to Newton's law of gravitation and rearranging.

Question 29

What is the surface gravity?

Answer 29

The magnitude of g (with arrow above)

Question 30

What are the consequence of the equation for the acceleration due to gravity?

Answer 30

1) Bodies accelerate as they fall; 2) All bodies accelerate (fall) at the same rate, irrespective of their mass. On earth air resistance interferes and we do not always see this affect, an example of this is Apollo 15 mission dropped a hammer and a feather at the same time.

Question 31

For two planets, how do you find which planet has the higher surface gravity?

Answer 31

1) If two planets have the same average density, the larger planet will have the higher surface gravity. 2) If two planets have the same radius, the denser planet will have the higher surface gravity.

Question 32

The minimum velocity needed for a projectile, that has been launched vertically upwards to escape the gravitational pull of the planet is set up by ______________.

Answer 32

Totalling up all forms of energy (kinetic and potential) and setting it to zero.

Question 33

Why are planets and moons subjected to differential forces?

Answer 33

Planets and moons experience differential forces as a result of their mass distributions. We observe this differential effect with, for example, the Earth's tides due to the Moon (as well as the Sun).

Question 34

As the Moon orbits the Earth, the location of these tides move with it, when do spring and neap tides occur?

Answer 34

1) Exceptionally high (spring) tides can occur when the Earth, the Moon and the Sun are all aligned. 2) Exceptionally low (neap) tides can occur when the Moon and the Sun sit at right angles from the perspective of the Earth.

Question 35

The atmospheres of the planets (and the stars_ can be modelled as an . . .

Answer 35

. . . ideal gas assuming point like particles(i.e. assuming that the atoms or molecules have no physical extent of volume associated with them (interacting in perfectly elastic collisions (i.e. with no energy loss).

Question 36

What is the V{rms}?

Answer 36

The root mean square speed, V{rms} is a measure of the average speed of the particles in the gas.

Question 37

The temperature of the gas is linked to _______________.

Answer 37

The temperature of the gas is linked to the average kinetic energy of its particles.

Question 38

What happens when the gas reaches a temperature of absolute zero?

Answer 38

The mean square speed equals zero and therefore all gas motions cease and the gas pressure drops to 0K.

Question 39

A particle escapes from a planet of Mass M{p}, radius R{p} if it has speed

Answer 39

V > V{esc}

Question 40

In a gas, do all particles have the same speed?

Answer 40

No, they do not. There is a distribution of particle velocities within the gas. Thus, some particles will escape the planet's gravitational pull and others will not.

Question 41

What happens when a sufficient fraction of particles exceed the escape velocity?

Answer 41

When a sufficient amount of particles exceed the planet's escape velocity, the planet will effectively lose its atmosphere. A particular component (i.e. one particular chemical element in the gas) will be lost if for that component: V{rms} > 1/6 V{esc}

Question 42

The more massive a planet is, the ______ the atmosphere's temperature must be before a particular atmospheric component is lost.

Answer 42

Higher

Question 43

What is the scale height, Hp?

Answer 43

The scale height is the height over which pressure decreases (or increases) by a factor of e=2.718.

Question 44

What does the value of the scale height tell us?

Answer 44

In a planetary atmosphere, the value of the scale height tells you something about how quickly the atmosphere "thins out" from the surface of the planet.

Question 45

What does "Isothermal" mean?

Answer 45

Isothermal means "equal heats" or, in our case a temperature that does not change throughout the atmosphere.

Question 46

List the features of the Jovian Planets

Answer 46

1) Higher mass, larger radii 2) Distant from the Sun 3) Lower surface temperature 4) Lower Average Density 5) Atmosphere abundant H & He 6) Gaseous & Liquid with rocky core 7) Rapid Rotation period 8) Many planetary rings and natural satellites

Question 47

List the features of the Terrestrial Planets

Answer 47

1) Lower mass, smaller radii 2) Near from the Sun 3) Higher surface temperature 4) Higher Average Density 5) Atmosphere depleted of H & He 6) Solid Surface 7) Slower Rotation period 8) No planetary rings and few natural satellites

Question 48

The internal structure of the Jovian planets can be broken into three main regions: upper atmosphere, lower atmosphere and the core. Describe the upper atmosphere of Jupiter

Answer 48

The upper atmosphere is comprised of approximately 90% molecular hydrogen, 10% helium and 0.2% methane, ammonia and water. The temperature is 170K.

Question 49

The internal structure of the Jovian planets can be broken into three main regions: upper atmosphere, lower atmosphere and the core. Describe the lower atmosphere of Jupiter

Answer 49

The high pressure and density in this region compresses the hydrogen, breaking the molecular bonds so that electrons are shared between atoms in a metal. We call this "liquid metallic hydrogen". This metallic hyrdogen is what gives Jupiter a strong magnetic field, 19,000 times that of earth. The temperature is 10,000K.

Question 50

The internal structure of the Jovian planets can be broken into three main regions: upper atmosphere, lower atmosphere and the core. Describe the core of Jupiter

Answer 50

Solid and rocky at very high pressure and density, made up from magnesium, silicon, iron and "liquid ices" (water, methane and ammonia in a somewhat fluid state because they are under extremely high pressure). The core is about 10-15 times as massive as the Earth and shows evidence of internal heating due to gravitational energy released in the formation pf the planet. The temperature is 20,000K.

Question 51

The internal structure of the Jovian planets can be broken into three main regions: upper atmosphere, lower atmosphere and the core. Describe the upper atmosphere of Saturn

Answer 51

The upper atmosphere is comprised of approximately 97% molecular hydrogen, 3% helium and 0.2% methane, ammonia and water. The temperature is 135K.

Question 52

The internal structure of the Jovian planets can be broken into three main regions: upper atmosphere, lower atmosphere and the core. Describe the lower atmosphere of Saturn.

Answer 52

Liquid metallic hydrogen as on Jupiter but at a much greater depth due to comparably low mass and density. The temperature is 8,000K.

Question 53

The internal structure of the Jovian planets can be broken into three main regions: upper atmosphere, lower atmosphere and the core. Describe the core of Saturn.

Answer 53

A dense "soup" of rock and liquid ices as on Jupiter but with a mass about 13 times that of the Earth. The temperature is 14,000K.

Question 54

The internal structure of the Jovian planets can be broken into three main regions: upper atmosphere, lower atmosphere and the core. Describe the upper atmospheres for Uranus and Neptune.

Answer 54

The upper atmospheres are comprised of approximately 83%/74% molecular hydrogen, 15%/25% helium and 2%/1% methane on Uranus/Neptune respectively. The temperature is 80K.

Question 55

The internal structure of the Jovian planets can be broken into three main regions: upper atmosphere, lower atmosphere and the core. Describe the lower atmosphere for Uranus and Neptune.

Answer 55

The pressures here are not high enough for liquid metallic hydrogen to form and, as a a consequence, the magnetic fields are weaker then on Jupiter and Saturn. The magnetic fields on Uranus and Neptune arise from the "Ionic ocean" of ionised molecules. The temperature is 2,500K.

Question 56

The internal structure of the Jovian planets can be broken into three main regions: upper atmosphere, lower atmosphere and the core. Describe the cores of Uranus and Neptune.

Answer 56

A dense "soup" of rock and liquid ices as on Saturn with a mass about 13 times that of the Earth. The cores of Uranus and Neptune form a much higher fraction (70% to 90%) of the total mass of these planets compared to Jupiter (5%) and Saturn (14%). The temperature is 7,000K.

Question 57

State an example that shows that the Jovian planets rotate differentially.

Answer 57

On Jupiter, there are cloud bands completely circling the planet. Because of the differential motion some bands move slower than others and APPEAR to move in opposite directions to each other.

Question 58

On Jupiter, zones can be described as ____________.

Answer 58

Regions of relatively high pressure

Question 59

On Jupiter, belts can be described as ____________.

Answer 59

lower pressure regions

Question 60

Why are the Jovian planets oblate?

Answer 60

The Jovian planets are significantly flattened, or oblate due to their rapid rotation (large centrifugal force) and fluid interior. The smaller the core, the larger the oblateness - this means Jupiter and Saturn are very oblate.