The Cosmic Perspective Chapter 11 - Mastering Astronomy

The two jovian planets that contain the highest proportions of hydrogen compounds are

Uranus and Neptune

Enceladus

Spacecraft images show fountains of ice spraying into space from Saturn's moon

IO

the most volcanically active world in the solar system

jovian moon with the most geologically active surface

Europa

Jupiter has three moons

evidence of a global, subsurface ocean of liquid water,

with the strongest evidence favoring an ocean

surface features and magnetic field data support the existence of a subsurface ocean

Tidal heating

responsible for the tremendous volcanic activity on Io.

Callisto

most distant of Jupiter's four Galilean moons.

orbital resonance.

Europa orbits Jupiter twice for every one orbit of Ganymede

when one moon's orbital period is a simple fraction of the other's, such as 1/2 or 1/3 or 1/4.

IO characteristics

- source of ionized gas in the donut-shaped charged particle belt around jupiter

- hot, glowing lava visible in some photos

- volcanoes currently erupting

Europa Characteristics

- surface features provide evidence of a subsurface liquid ocean

- ice covered surface with few impact craters

Ganymede Characteristics

largest moon in the solar system

- heavily cratered terrain adjacent to much younger terrain

Jupiter's Largest Moons

Mercury

Titan

Ganymede

Ganymede

Jupiter's Largest moon

Titan

Lakes of liquid methane and ethane

The nature of planetary rings

composed of countless individual particles.

ranging from dust grains to large boulders,

orbits its planet independently in accord with Kepler's laws.

Early Mars

Strong greenhouse effect.

Strong magnetosphere.

Substantial volcanism and outgassing.

Some craters held lakes of water.

Core convection.

mars Today

Surface pressure too low for stable liquid water.

Very weak greenhouse effect.

Solar wind strips atmospheric gas.

Early Mars had both core convection and a strong magnetosphere. What is the connection between these two things?

Core convection helps generate a magnetic field,

magnetic field creates the magnetosphere.

combination of convection in its molten metal core and a relatively rapid rotation rate.

The magnetic field created the magnetosphere that shielded the atmosphere from the solar wind.

Why Mars changed so much from its early conditions to its conditions today

Interior cooling.

why core convection stopped,

leading to weakening of the magnetic field and magnetosphere,

why volcanism and outgassing became so much weaker.

why Mars has lost so much more interior heat than Earth.

Mars is smaller than Earth.

Smaller objects cool more rapidly than large ones,

loss of its magnetosphere, allowing the solar wind to strip atmospheric gas away.

It has measured rates of gas loss from the atmosphere today.

Mars is still losing gas to solar wind stripping,

Atmosphereic Pressure on Earth

1 Bar

Sea-Level Pressure on earth

Pressure greater than 1 bar

Higher pressure

Pressure Less than 1 bar

Lower pressure

Lowest to Highest Altitude

Troposphere

Stratosphere

Thermosphere

Exosphere

Troposphere

Convection and weather occur primarily

The greenhouse effect causes warming

Stratosphere

Ultraviolet light from the Sun is absorbed primarily in Eath's

Thermosphere

X-rays from the Sun are absorbed primarily in Eath's

Exosphere

The "edge of space" occurs

Why doesn't Mars and Venus have a stratosphere?

It lacks a layer of ultraviolet absorbing gas

Planets Closest to farthest to the Sun

Earth

Jupiter

Saturn

Uranus

Neptune

Planets from smallest to largest radius

Earth

Neptune

uranus

Saturn

Jupiter

Planets from lowest to highest mass

Earth,

Uranus,

Neptune,

Saturn,

Jupiter

Jupiter and Saturn

interior is mostly liquid or metallic hydrogen;

composed of Helium and Hydrogen

Uranus and Neptune

blue color from Methane

composed of mostly hydrogen compounds

All Four Jovian Planets

approx 10 Earth-mass core;

orbited by rings of ice and rock;

have magnetic fields stronger than Earth's;

strong atmospheric winds and storms

No Jovian Planets

Solid Surface

General pattern of composition among Jovian Planets

Uranus and Neptune contain relatively more rock and hydrogen compounds than Jupiter and Saturn.

Is there a clear trend in jovian planet densities with mass or distance from the Sun?

There is no clear trend in the densities with mass or distance.

why the densities of Uranus and Neptune are higher than that of Saturn, even though Saturn is much more massive?

They have a higher proportion of hydrogen compounds and rock

hydrogen compounds and rock are much higher in density

Uranus and Neptune are higher in density

because they are made primarily of higher-density hydrogen compounds and rock.

Why Jupiter's density is higher than Saturn's

Jupiter is more massive than Saturn.

its interior is more compressed than Saturn's due to gravity and its mass

Based on the leading scientific theory of solar system formation, why Uranus and Neptune have a significantly different composition than Jupiter and Saturn?

Jupiter and Saturn captured more gas from the solar nebula than Uranus and Neptune.

Accretion occurred more rapidly in the denser regions of the solar nebula that were closer to the Sun

accreted so much hydrogen and helium gas that these ingredients ended up dominating their composition.

Io experiences tidal heating primarily because

Io's elliptical orbit causes the tidal force on Io to vary as it orbits Jupiter

The strength of the tidal force depends on Io's distance from Jupiter,

This orbital resonance causes Io to have a more elliptical orbit than it would otherwise, because

Io, Europa and Ganymede periodically return to the same orbital positions, creating the same gravitational tugs

What observational evidence confirms that tidal heating is important on Io?

active volcanoes on Io

We cannot see tidal forces or tidal heating; .

it must have an ongoing internal heat source, which we identify as tidal heating.

Europa experiences less tidal heating than Io,

because Europa is farther from Jupiter than Io.

Jupiter's gravity exerts the primary tidal force on the Galilean moons,

Io is closest to Jupiter and therefore experiences the most tidal heating;

What additional information, if any, would we need to decide whether these moons experience tidal heating?

We need to know their orbital periods

We expect tidal heating to be possible only if there is an orbital resonance that helps maintain an elliptical orbit.

Saturn's rings are composed of

lots of individual particles of ice and rock

ranging in size from dust grains to small boulders.

Saturn's rings look bright because

light from the Sun reflects off the icy particles in the rings

the motion of the particles in Saturn's rings

Particles in the inner rings orbit Saturn at a faster speed than particles in the outer rings.

According to Kepler's Third Law