ch07 rg astro solar system

geller

View of the solar system from above

Orbits are nearly circular

View of the solar system from the side

Orbits are all in nearly the same plane

Terrestrial planets

Four small inner planets (Mercury, Venus, Earth, Mars) Resemble Earth

• Have hard, rocky surfaces with mountains, craters, valleys and volcanos.

Jovian planets

Four large outer planets (Jupiter, Saturn, Uranus, Neptune) Resemble Jupiter

• The materials that make up these planets are mostly gaseous or liquid.

• Visible “surface” features of a jovian planet are actually cloud formations in the planet’s atmosphere

Are terrestrial or jovian planets bigger?

Jovian planets

• Have masses that range from tens to hundreds of times greater than the mass of any of the terrestrial planets.

Density definition

The mass of an object divided by its volume.

What does chemical differentiation suggest on density?

• Low-density materials rise to the surface, high-density materials sank deep into Earth’s interior

Do terrestrial planets or jovian planets have a higher density?

• Terrestrial planets —> Have dense iron cores

Which elements do the giant outer planets are composed primarily of?

Light elements such as hydrogen and helium

Which planets have interiors made mostly of gas and liquid and NO solid surface?

Jovian planets

Which planets DO NOT have moons?

Mercury and Venus

Small planets with low gravity can’t hold onto hydrogen and helium gasses.

1. A given planet’s size and mass has a corresponding ESCAPE SPEED.

2. Atoms or molecules moving at speeds ABOVE the escape speed simply leave the atmosphere of the planet. This prevents small planets from accumulating hydrogen/helium, which are the most abundant materials. (In fact, to keep a gas, its average molecular speed should be LESS than 1/6th of the ESCAPE SPEED)

3. Temperature of gas determines the average speed, and this temperature is determined by distance from the Sun

The largest moons

• Moon

• Io

• Europa

• Ganymede

• Callisto

• Titan

• Triton

Moon, Io and Europa have relatively high average densities, indicating that these moons are made primarily of rocky materials.

By contract, the average densities of Ganymede, Callisto, Titan, and Triton are all relatively low

—> Contain substantial amounts of water ice (LESS DENSE THAN ROCK)

Jupiter’s satellite Io is the most geologically active world in the solar system FOR WHAT reason?

Due to its numerous volcanoes that continually belch forth sulfur rich compounds

The fractured surface of Europa, another one of Jupiter’s large satellites, was an early clue that…

That a worldwide ocean of liquid water lies beneath its icy surface.

Titan (Saturn’s moon) fun facts

• Liquid methane and ethane —LAKES

• Has a “methane cycle” analogous to Earth’s hydrological cycle

• In Titan’s low gravity, GRAPE-SIZED rain drops would slowly fall to the ground!

• With light-weight wing attachments to arms, humans could FLY around in Titan’s low-gravity and thick atmosphere!

Titan has ICE VOLCANOES

Cryovolcanism

Titan has 100 km “sand” dunes with grains of?

Water-ice mixed with hydrocarbons

The absorption lines of methane (CH4) are produced in

Titan’s atmosphere

The absorption line of oxygen (O2) is produced in

Earth’s atmosphere

The absorption line of hydrogen (H) is produced in

Sun’s atmosphere

Titan lines Doppler shifts back and forth

The spectrum of Europa is almost identical to that of ice, indicating that its surface is MOSTLY ice, not rock

While Jupiter and Saturn lack a solid surface, their many moons contain

A rich variety of features

On Earth, spectroscopy is a very useful tool for assessing

vegetation and greenhouse gases in our atmosphere

How does spectroscopy help us determine the atmosphere of a planet?

1. Look at particular wavelengths absorbed AND the amount of light absorbed at these wavelengths

2. Both of these depend on the kinds of chemicals present in the planet’s atmosphere and the abundance of those chemicals.

What molecules are dominant in Titan’s atmosphere?

• Titan’s ultraviolet spectrum shows nitrogen molecules (N2) are dominant

• Titan’s spectral lines includes a variety of molecules that contain carbon and hydrogen

What heavy elements are the terrestrial planets made of?

• Iron

• Oxygen

• Silicon

• Magnesium

• Nickel

• Sulfur

Distance from the Sun (Terrestrial VS Jovian)

• Terrestrial —> LESS than 2 AU

• Jovan —> MORE than 5 AU

A planet’s surface temperature is related to its distance from the Sun

• H2 (hydrogen) and He (helium) are gaseous EXCEPT at extremely LOW temperatures and extraordinarily HIGH temperatures

• Rock-forming substances such as iron and silicons are SOLIDS except at temperatures ABOVE 1000 K.

Why do massive and slow moving molecules such as CO2, N2, O2, and water vapor (H2O) surround the terrestrial planets?

Atmospheric temperatures are HIGH, low-mass hydrogen molecules and helium atoms move so SWIFTLY that they can ESCAPE from the WEAK gravity of the planets.

Asteroids

Found in the inner solar system

Trans-Neptunian objects

Found beyond Neptune in the outer solar system and contain BOTH rock and ice

Comets

Mixtures of rock and ice that originate in the outer solar system that can venture close to the Sun

• BLUISH tail of GAS

• WHITE tail of DUST

• TRANS-NEPTUNIAN

What determines how smooth versus cratered a planet or moon surface appears?

Big planets had longer period of volcanism to erase craters!

—> expect “big = smooth” and “small = cratered”

Compared to planet #1, planet #2:

• Has ½ the radius

• Has ¼ the surface area (so it can lose heat only ¼ as fast)

• But has only 1/8 the volume (so it has only 1/8 as much heat to lose)

Hence compared to planet #1, planet #2:

• Will COOL OFF MORE rapidly

• Will sustain LESS geologic activity

• Will have MORE CRATERS

Where is the asteroid belt located?

Between Mars and Jupiter

Kuiper Belt

Extends from around the orbit of Pluto to about 500 AU from the Sun

• Most Trans-Neptunian objects orbit here

Oort Cloud

Forms a spherical “halo” around the solar system, extends to 50,000 AU from the Sun

Meteroids

Smaller craters

What do magnetic fields tell us about a planet?

A planet (or moon’s GLOBAL magnetic field comes from electrical currents flowing in a molten interior!

• This allows use to measure magnetism on the outside and learn about the inside.

Unexpected magnetism on Mars

Suggests (past) plate tectonics!

Magnetic fields for terrestrial planets

• Mercury —> WEAK magnetic field

• Venus —> NO magnetic field

• Earth —> MODERATE, due to liquid iron core

• Mars —> NO magnetic field

Atmosphere for terrestrial planets

• Mercury —> NO atmosphere

• Venus —> Carbon Dioxide

• Earth —> Nitrogen, Oxygen

• Mars —> Carbon Dioxide

Magnetic field for Jovian planets

• Jupiter —> STRONG, due to liquid metallic hydrogen

• Saturn —> STRONG, due to liquid metallic hydrogen

• Uranus —> MODERATE, due to dissolved ions

• Neptune —> MODERATE, due to dissolved ions

Layout of Solar System

1. Inner terrestrials

2. Asteroid belt

3. Outer-giants

4. Trans-Neptunian objects

5. Kuiper-belt ice balls

6. Oort Cloud

The most intense planetary magnetic field in the solar system is that of ?

Jupiter

Liquid metallic hydrogen

Hydrogen compressed to such a density that it behaves like a Liquid Metal