chapter 7physics.unm.edu/.../lectures/07_lecture_outline_rev.pdf · 2020-03-03 · 7.0 the jovian...

Astronomy A BEGINNER’S GUIDE

TO THE UNIVERSE EIGHTH EDITION

CHAPTER 7

The Jovian Planets Lecture Presentation

© 2017 Pearson Education, Inc.

7.0 The Jovian Planets: Jupiter … Neptune

The Jovians are significantly further from the Sun than the Terrestrial planets -- so the heat energy they receive from the Sun is “tiny”! Do you expect the planet temperatures to be much warmer or much colder than Earth?

7.0 The Jovian Planets: Jupiter … Neptune

This figure shows the solar system from a vantage point that emphasizes the relationship of the jovian planets to the rest of the system.

7.1 Observations of Jupiter and Saturn •  Jupiter’s major features can be seen from Earth, even

with a small telescope. •  Here: Jupiter with its 4 Galilean moons


7.1 Observations of Jupiter and Saturn

•  True-color image of Jupiter; what is most notable is Jupiter’s banded appearance!


7.1 Observations of Jupiter and Saturn


Natural-color image of Saturn shows the delicate coloration of the cloud patterns on Saturn; what is most notable are Saturn’s rings!

7.1 Observations of Jupiter and Saturn View of Saturn’s rings from Earth changes as Saturn orbits the Sun! Every approximately 14.5 years the rings are edge-on and briefly vanish!

Seeing is believing!

7.2 The Discoveries of Uranus and Neptune

Bahamas’ water color is similar as water also absorbs orange and red light!

Why is Uranus blue-green? Apparently methane (CH4) gas in Uranus’ atmosphere absorbs the red light and reflects the blue light from the Sun!

Uranus, in natural color; what is most notable is Uranus’ featureless appearance! This may be because Uranus has no internal heat source!

7.2 The Discoveries of Uranus and Neptune •  Neptune in natural color. What is most notable is Neptune’s

deep blue coloration! Maybe this is because Uranus’ fraction of methane (CH4 ) is about 2x Neptune’s.


1989 showed Great Dark Spot

2018 new dark tempest storm

7.3 Bulk Properties of the Jovian Planets The Jovian planets are large and much less dense than the terrestrial planets. Their large escape speed and low temperature allow them to retain hydrogen and helium atmospheres!


7.3 Bulk Properties of the Jovian Planets The Jovian planets are much colder than the terrestrial planets thus their internal heat sources are important. Jupiter has the strongest magnetic field of any planet.


7.3 Bulk Properties of the Jovian Planets

Earth is tiny in comparison!

7.3 Bulk Properties of the Jovian Planets Jovians and Terrestrials have very different atmospheres!


7.3 Bulk Properties of the Jovian Planets Jovian atmosphere have Hydrogen (H) and Helium (He) as their dominant components. Saturn appears to have a very low fraction of helium! This may be related to a helium rain internal heat source!


7.3 Bulk Properties of the Jovian Planets

Having no solid surface, the jovians exhibit differential rotation.

•  Mass: 1.9 × 1027 kg (twice that of all other planets put together)

•  Radius: 71,500 km (112 times Earth’s)

•  Density: 1300 kg/m3—cannot be as rocky or metallic as the inner planets.

7.3 Bulk Properties: Jupiter

•  Rotation rate: Problematic, as Jupiter has no solid surface; different parts of the atmosphere rotate at different rates. This is called “differential rotation”: 9hr 50min at equator and 9hr 56min at poles.

•  Note Jupiter’s immense magnetic field is strongest of all the planets!

•  Jupiter’s magnetic field rotation period is 9hr 55min, less than half of Earth’s!

7.3 Bulk Properties: Jupiter

Mass: 5.7 × 1026 kg

Radius: 60,000 km

Density: 700 kg/m3 — less than water!

Rotation: differential: 10hr 14min at equator and 10hr 39min near poles, and rapid enough to make Saturn considerably oblate (“pumpkin shaped”)

7.3 Bulk Properties: Saturn

Pumpkin shaped

Ball shaped

7.3 Bulk Properties of the Jovian Planets •  Jovian planet rotation axes compared to Earth and

Mars: •  Jupiter’s axis is more vertical (to plane of orbit) •  Saturn and Neptune are somewhat more tilted •  Uranus’ axis is almost in the orbit plane!


7.3 Bulk Properties of the Jovian Planets •  Peculiarity of Uranus: axis of rotation is tilted by 98o

(to orbit plane) thus lies almost in the plane of its orbit.


Uranus’ seasonal variations are extreme.

7.4 Jupiter’s Atmosphere


Jupiter’s atmosphere has several distinct features

Cooler and higher

Warmer and lower

7.4 Jupiter’s Atmosphere •  Jupiter’s atmosphere has bright

zones and dark belts. •  The bright (light colored) zones

are probably ammonia ice. •  Zones are cooler and are higher

than belts. •  Belts are warmer and lower

(than zones). •  Stable flow underlies zones and

belts, called zonal flow. •  Simplified model is given here:


7.4 Jupiter’s Atmosphere Jupiter’s belted cloud layers are probably caused by Jupiter’s internal heat source that energizes atmospheric convection.


Chapt 5: 5.3 Atmosphere Layers Convection is a “stirring” that occurs naturally within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity.




For a time lapse video look at: https://en.wikipedia.org/wiki/File:Jupiter_from_Voyager_1_PIA02855_max_quality.ogv



Where on Jupiter is there a total Solar eclipse “right now”?

7.4 Jupiter’s Atmosphere •  Jupiter has no

solid surface so we choose the top of troposphere = 0 km.

•  Lowest cloud layer (water ice) cannot be seen in visible light.


7.4 Jupiter’s Atmosphere •  Jupiter’s

atmosphere is about 90% hydrogen (H2) and 10% helium (He),

•  For comparison the Sun is about 91% hydrogen and 9% helium.


Jupiter’s atmosphere has a small amount of methane (CH4), ammonia (NH3) and water (H2O) vapor.

Atmospheric color probably from complex chemical interactions


Jupiter is basically a turbulent, stormy, whirlpool of wind, banded with variable belts and a giant Red Spot.



The giant Red Spot storm, has been raging since at least the late 1600s – when Italian astronomer Giovanni Cassini made the first recorded observation of it.

This giant Red Spot is an oval shaped, counter-clockwise moving storm and is four times larger than our Earth.

7.5 Saturn’s Atmosphere •  Saturn’s atmosphere

is somewhat colder and its atmosphere is thicker than Jupiter’s.

•  It is also expected to have three cloud layers.

•  The atmosphere of Saturn is about 96% hydrogen (H2) and 4% Helium (He).

These layers are not observable in visible light.

7.5 Saturn’s Atmosphere

While Saturn’s atmosphere also shows zone and belt structure, the zones/belts are much fainter than on Jupiter.

7.5 Saturn’s Atmosphere •  Saturn also has large storms. This storm, which generated its

own band, was observed by the Cassini spacecraft in 2011 in visible light (a), and after that faded it was still visible in the infrared (b).


7.5 Saturn’s Atmosphere


•  Saturn, curiously like Earth and Venus, has enormous polar vortices that resemble huge storm systems.

•  The northern polar vortex, sometimes called Saturn’s hexagon, is shown in the bottom image, southern polar vortex on the top.

7.5 Uranus and Neptune Atmosphere

Outer atmospheres of Uranus [about 83% hydrogen (H2), 15% Helium (He) and 2% methane (CH4)] and Neptune [about 80% hydrogen (H2), 19% Helium (He) and 1% methane (CH4)] have “large” methane fractions!

Uranus


Its all about temperature. Uranus and Neptune are cold enough that ammonia (NH3) freezes (and sinks) leaving methane (CH4) to dominate and give the characteristic green/blue color.


Uranus Neptune


•  Rotation of Uranus can be measured by watching storms.



•  Neptune has storm systems similar to those on Jupiter, but fewer. The large “Great Dark Spot” storm system in (b) [below] has disappeared in recent years.


7.6 Probable Jovian Interiors •  No direct information is available about jovian interiors, but their

main components, hydrogen and helium, are quite well understood.

(https://earthsky.org/space/why-neptune-uranus-different-collisions )

Most jovian planets get their heat from the Sun and from their interiors! Jupiter creates a lot of internal heat and releases this heat by emitting thermal radiation. In fact, Jupiter creates so much internal heat that it emits almost twice as much energy as it receives from the Sun. The only reasonable explanation is that Jupiter is still slowly contracting due to gravity, almost as though it has not quite finished forming. Also, it may still be cooling down: losing the heat energy from its initial formation (like star formation in Chapt 11).

7.6 Probable Jovian Interiors

Saturn and Neptune also appear to be emitting more energy than they receive from the Sun. For Saturn we believe that atmospheric helium and hydrogen are not well mixed. Helium tends to condense into droplets (helium rain) that then fall, in Saturn’s gravitational field, producing heat energy! This is thought to be why Saturn’s upper atmosphere is only 4% Helium (He). Uranus is the only jovian planet not emitting excess internal energy. Perhaps this is the reason for Uranus’ featureless appearance.

7.6 Probable Jovian Interiors

7.6 Jovian Magnetic Fields •  Jupiter and Saturn have large magnetic fields that

are at a small angle to their rotation axis


Jupiter is surrounded by belts of charged particles, much like the Van Allen belts but vastly larger.

7.6 Jupiter’s Magnetosphere

Jupiter’s magnetosphere is enormous (see next slide).

7.6 Jupiter’s Magnetosphere •  Jupiter’s

magnetosphere: – Strongest

magnetic field of all the planets.

– Magnetosphere has been detected beyond the orbit of Saturn.


7.6 Jupiter’s Magnetosphere Aurorae are seen on Jupiter and have the same cause as those on Earth: solar wind charged particles spiral down Jupiter’s magnetic field lines to make aurorae! But on Jupiter, the auroral activity is much more intense and rarely stops.


From Chapt 5.7 Magnetospheres Charged particles from the Sun spiral down magnetic field lines in Earth’s magnetosphere and collide with atmospheric atoms; when they do, they create glowing light called an aurora.

7.6 Saturn’s Magnetosphere Saturn also has a strong magnetic field, but only 5% as strong as Jupiter’s.

Solar wind charged particles also make aurorae near Saturn’s poles.


7.6 Jovian Magnetic Fields •  Uranus and Neptune both have substantial magnetic

fields, but at a large angle to their rotation axes.


7.6 Jovian Magnetic Fields •  The rectangle within each planet shows a bar magnet

that would produce a similar field. Note that both Uranus’s and Neptune’s are significantly off center.


7.7 (extra): Was Jupiter almost a Star? Could Jupiter have been a star? No; it is too small and thus never hot enough to become a star. It would need to be about 80 times more massive to be even a very faint star.

Even though not a star Jupiter was likely very luminous when our solar system was forming: The energy released from gravitational collapse/compression meant that when Jupiter was first forming meant Jupiter could have been 100 times brighter than the Moon, as seen today from Earth!

Summary of Chapter 7 •  Jupiter and Saturn were known to the ancients;

Uranus was discovered by chance, and Neptune was predicted from anomalies in the orbit of Uranus.

•  Jovian planets are large but not dense; they are fluid and display differential rotation.

•  Cloud layers have light zones and dark bands; wind pattern, called zonal flow, is stable.


Summary of Chapter 7 (con’t) •  Storms appear with regularity; the Great Red Spot of

Jupiter has lasted for hundreds of years (that we know of).

•  Due to conductive interiors and rapid rotation, Jovian planets have large magnetic fields.

•  Jupiter, Saturn, and Neptune radiate more energy than they receive from the Sun.


chapter 7physics.unm.edu/.../lectures/07_lecture_outline_rev.pdf · 2020-03-03 · 7.0 the jovian...

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