Section 5 - The Gas Giants Flashcards
1
Q
- Describe the orbital eccentricity and obliquity of the giant planets.
- Describe the masses of the giant planets.
- How dense are Jupiter and Saturn?
A
- Have the least perturbed (eccentric) orbits of the Solar System planets. All close to circular, and well aligned with the ecliptic plane.
- Jupiter and Saturn dominate the planetary mass of the Solar System. Masses and radii of Uranus and Neptune are intermediate between the terrestrial planets and gas giants.
- Least dense planets in solar system.
2
Q
- If the masses and radii of the planets are compared with mass-radius relations for different compositions, what does this show?
- Compare the densities of Uranus and Neptune to those of Saturn and Jupiter.
- What is the most likely composition of Uranus and Neptune?
- What causes the ice giants’ intermediate location on mass-radius diagram?
A
- Terrestrial planets have a rocky composition with iron core, Jupiter and Saturn dominated by H and He gas. Uranus and Neptune have an intermediate composition, requiring ice/rock and gas.
- Densities are much higher.
- Density requires gas, so likely to include other volatiles too e.g. water, ammonia, methane which are more abundant than refractory elements and form ices at low temp. Dominant ice, as 10x more methane in atmospheres than gas giants.
- Ice dominates the mass, but gas dominates the volume.
3
Q
- Why are the radii of gas giant planets around the mass of Jupiter approximately independent of mass?
- Describe the interior structure of the gas giants.
A
- An increase of mass is balanced by increased compression of the interior.
- Gas giants have distinct layers, gaseous H_2 dominated atmospheres above fluid molecular H_2 envelopes, above a layer dominated by liquid metallic H. Believed to have ice/rock/iron cores.
4
Q
- How fast do Jupiter and Saturn rotate?
- What does this lead to?
- What does this mean for their gravitational fields?
- Describe the magnetic fields of Jupiter and Saturn.
- Why is the magnetic dipole moment of Jupiter 30x stronger?
A
- Very rapidly
- Very high oblateness, b = (R_e - R_p)/R_e where R_e is the equatorial radius, and R_p is the polar radius.
- Gravitational field differs from a point source, allowing the internal density structure to be determined.
- Both have strong magnetic fields since they have conducting interiors, rapid rotation, and convection. Generated by magnetic dynamos acting in the conducting liquid metallic hydrogen interior.
- Higher internal pressure and so larger volume of metallic H.
5
Q
- What does the strong magnetosphere of Jupiter do?
- Why is its magnetosphere much larger than that of the Earth?
A
- Shields the atmosphere from the solar wind.
- Stronger dipole moment and weaker solar wind at Jupiter.
6
Q
- Describe the rotation of the ice giants and what this causes.
- Describe the obliquities of the ice giants.
- Describe the magnetic fields of Uranus and Neptune.
A
- Rapidly rotating and hence oblate and internal density profiles constrained by gravitational moments.
- Both have high obliquities and Uranus has anomalously high obliquity of more than 90 degrees (so retrograde rotation).
- Have strong magnetic fields, stronger than Earth. Must arise from a magnetic dynamo in the fluid icy material where pressure is sufficient to ionise fluid ices, as the pressure in the gaseous envelope is not high enough for hydrogen to enter metallic phase.
7
Q
Uranus and Neptune have unusually offset _____ from their spin axis and the _____ of the planets. Leads to more complex __________.
A
dipoles, centre, magnetospheres
8
Q
Internal heat:
- Measured effective temperatures of Jupiter, Saturn and Neptune are significantly _____ than their calculated ________ temperatures.
- Effective temperature is….
- Equilibrium temperature is…..
- High effective temperatures imply significant sources of….
- What causes this on each planet?
A
- Higher, equilibrium
- Effective temperature is temperature of the blackbody that would have the same total luminosity as the thermal emission of the planet.
- Equilibrium temperature is calculated by equating heating from the Sun and blackbody cooling.
- Internal heat
- For Jupiter, residual heat from gravitational collapse at formation, and on Saturn as well atmospheres deficient in He suggests rainout of He in interior contributes. Neptune may also be undergoing continuing differentiation.
9
Q
- The atmosphere of Jupiter has bright zones and dark belts. What are these due to?
- Describe Jupiter’s winds.
- Saturn has similar banding to Jupiter but more muted. Why is this?
A
- Bright zones are due to reflective clouds (ammonia ice in top layer, then ammonium hyrdosulfide, then water). Where warm gas is rising, clouds condense and the gas cools. Dark belts are where cool material sinks, clouds evaporate as they are heated.
- Has strong winds running in opposite directions in zones and belts. Surface view of global convection pattern that extends deep into interior.
- Clouds condense deeper in the atmosphere which is cooler than Jupiter.
10
Q
- Neptune also has a pattern of cloud bands, even more muted than Saturn. Why?
- Why is Neptune blue?
- Why does Neptune have dark spots? What drives these?
- What seasonal variations have been noticed on Neptune?
A
- Atmosphere is cooler and clouds are forming deeper in the atmosphere.
- Methane gas above the cloud layers strongly absorbs red light. Methane bands much stronger in Uranus and Neptune, and the cloud decks are lower.
- Storm systems, forcing by solar radiation.
- Reflective clouds increasing in the Southern hemisphere as it moves into summer.
11
Q
Describe the visual of Uranus.
A
Uranus has a faint banding structure, and has seasonal variations with North pole covered in cloud as it approaches mid-summer.
12
Q
- What are the 4 Galilean moons of Jupiter?
- As you go down the list written on the answer card, there are _______ volatiles and impact craters (surface age). Volatile content may indicate formation in a __________ disc with a ________ gradient. Lack of cratering indicates……
- If Ganymede and Io are placed on the mass-radius diagram, how do they compare to other solar system bodies?
A
- Io, Europa, Ganymede and Callisto (in order of increasing distance from Jupiter)
- Increasing, circumplanetary disc, temperature, ongoing resurfacing.
- Io similar to the Moon, and has a differentiated rocky interior. Moon density drops with orbital separation, and Ganymede has much lower density, suggesting internal composition dominated by water. Ganymede larger than Mercury but less massive.
13
Q
- Describe the surface and geological activity on Io.
- What mean motion resonances are there of the Galilean moons with Jupiter, and what does this cause?
A
- Io has intense volcanism due to tidal heating, and the surface is young with no impact craters due to continuous resurfacing by volcanism.
- Io 1:1, Europa 2:1, Ganymede 4:1. So takes 4 Jupiter orbital periods for one Ganymede orbit etc. These cause eccentric orbits which are damped by tidal interaction with Jupiter and hence heating.
14
Q
- Describe the surface of Europa.
- Describe the surface of Ganymede.
A
- Europa less dense than Io, young water ice surface covered in cracks and lacks impact craters. Thought to have a sub-surface liquid water ocean below a thin ice crust. Regular resurfacing by liquid water.
- Thicker water ice crust, less cracking, and more impact craters than Europa.
15
Q
- What is the moon which takes up 96% of the mass of Saturn’s Moon system? How does it compare to Ganymede in size?
- Describe the atmosphere of Titan.
- Describe the surface and weather on titan.
A
- Titan, smaller but similar in mass and radius to Ganymede.
- Thick atmosphere dominated by nitrogen, and also contains methane.
- Surface shrouded by thick high-altitude haze of hydrocarbons. Evidence for methane rain and surface flows, and methane lakes. Has rounded boulders and pebbles of water ice.
