Touring the Solar System

The Sun: An Overview

The Solar System

The Sun is at the center of our Solar System.

The Sun makes up 99.85% of the mass of the solar system. (masssun = 2.0 x 1030 kg)

The Sun is 70% H2 and 28% He; less than 2% is metals. The sun converts the hydrogen to helium over time.

The Sun: 5,800K at the surface, 15,600,000K at core!

The Planets: An Overview

The Solar System

The terrestrial planets are planets that are small and rocky—Mercury, Venus, Earth, and Mars. Latin terra - earth

The Jovian planets are the huge gas giants—Jupiter, Saturn, Uranus, and Neptune. The God Jove = Jupiter.

Pluto does not fit into either the Jovian or the terrestrial category. It is not considered a planet anymore.

Terrestrial Planets

MercuryVenus Earth

Mars

Jovian Planets

Jupiter SaturnUranus Neptune

A.K.A. = Nicknames

• The terrestrial planets are also called the Rocky or the Inner planets.

• The Jovian planets are also called the Giant, Gas, or the Outer Planets.

Orbits of the Planets

The Planets: An Overview

The Solar System

Size is the most obvious difference between the terrestrial and Jovian planets.

Density, chemical makeup, and rate of rotation are other ways in which the two groups of planets differ.

Planetary Data

The Planets: An Overview

The Solar System

The Interiors of the Planets• The substances that make up the planets are

divided into three groups: gases, rocks, and ices.

The Atmosphere of the Planets• The Jovian planets have very thick atmospheres

of hydrogen, helium, methane, and ammonia.

• By contrast, the terrestrial planets, including Earth, have meager atmospheres at best.

Scale of the Planets

Formation of the Solar System

The Solar System

Nebular Theory• A nebula is a cloud of gas and/or dust in space.• According to the nebular theory, the sun and

planets formed from a rotating disk of dust and gases.

Formation of the Solar System

The Solar System

Planetesimals• Planetesimals are small, irregularly shaped. • They were the “seeds” that grew into what we

now know as our planets.

• They are formed as nebular dust coalesces by gravity.

Formation of the Universe

Planetary Composition, Distance from the Sun, and Melting Point

Mercury

Mercury: The Innermost Planet

The Terrestrial Planets

Mercury is the innermost and second smallest planet; it is hardly larger than Earth’s moon.

• Mercury has cratered highlands, much like the moon, and vast smooth terrains that resemble maria.

Surface Features

Surface Temperatures: Mercury has the greatest temperature extremes of any planet:100K to 700K.

Mercury: The Innermost Planet

The Terrestrial Planets

Mercury does not have season since there is almost no tilt to its orbit: 0.01° This is the lowest value of tilt of the 8 planets. No seasons!

Mercury’s atmosphere: 42% O2; 29% Na; 22% H2; 6% He; 0.5% K.

Mercury was visited by NASA's Mariner 10 in 1973 and 1974 (robotic space probe that visited both Venus and Mercury). Mariner is STILL orbiting the Sun, but is no longer transmitting (and is probably horribly damaged by the Sun’s energy.)

Venus

Currently, the MESSENGER space probe is orbiting Mercury and sending messages back to Earth.

Probe launch in 2004

First image of Mercury sent back to Earth (2008)

Venus

Venus: The Veiled Planet

The Terrestrial Planets

Surface Temperatures: The surface temperature of Venus reaches 737K and lows temperatures of 228K. The hottest planet in the solar system.

Venus’ atmosphere is 96.5% CO2; 3.5% N2.

Venus: The Veiled Planet

The Terrestrial Planets

Venus tilted axis: 177.4° This is the largest value of tilt of the 8 planets. Its north pole actually points downward.

Because it is tilted so far, Venus is the only planet to appear to rotate clockwise!!!

Venus: The Veiled Planet

The Terrestrial Planets

Venus is similar to Earth in size, density, mass, and location in the solar system. Thus, it has been referred to as “Earth’s twin.”

• Venus is covered in thick clouds that visible light cannot penetrate.

Surface Features

• About 80 percent of Venus’s surface consists of plains covered by volcanic flow.

Mars

Mars: The Red Planet

The Terrestrial Planets

The Martian Atmosphere• The Martian atmosphere has only 1 percent of

the density of Earth’s.

Surface Features• Most Martian surface features are old by Earth

standards. The highly cratered southern hemisphere is probably 3.5 billion to 4.5 billion years old.

• Although the atmosphere of Mars is very thin, extensive dust storms occur and may cause the color changes observed from Earth.

Mars: The Red Planet

The Terrestrial Planets

Water on Mars• Some areas of Mars exhibit drainage patterns

similar to those created by streams on Earth.• Images from the Mars Global Surveyor indicate

that groundwater has recently migrated to the surface.

Mars Tilted Axis: 25.2°. Mars has seasons!

Mars Temperature: 186K – 293K

Mars’ Atmosphere: 95.3% CO2; 2.7% N2; 1.6% Ar.

Orbiting spacecraft

• Mars is currently host to three functional orbiting spacecraft: Mars Odyssey, Mars Express, and the Mars Reconnaissance Orbiter. This is the most of any planet (other than Earth).

Surface Landers

• The surface is also home to the two Mars Exploration Rovers (Spirit and Opportunity) and several inert landers and rovers, both successful and unsuccessful. The Phoenix lander recently completed its mission on the surface.

Water on Mars

Water on Mars

• The Polar Landers have determined that there is water on Mars!!!

• Liquid water cannot exist on the surface of Mars with its present low atmospheric pressure, except at the lowest elevations for short periods.

Water on Mars

• Water ice is plentiful on Mars, with two polar ice caps made largely of ice.

• In March 2007, NASA announced that the volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters.

Jupiter and the Great Red Spot

Jupiter: Giant Among Planets

The Outer Planets

Jupiter has a mass that is 2 1/2 times greater than the mass of all the other planets and moons combined.

• Jupiter’s hydrogen-helium atmosphere also contains small amounts of methane, ammonia, water, and sulfur compounds.

Structure of Jupiter

Jupiter: Giant Among Planets

The Outer Planets

• Jupiter’s satellite system, including the 28 moons (63 total satellites) discovered so far, resembles a miniature solar system.

Jupiter’s Moons

Jupiter’s Rings• Jupiter’s ring system was one of the most

unexpected discoveries made by Voyager 1.

Jupiter: Giant Among Planets

The Outer Planets

Jupiter’s Tilted Axis: 3.13°

Jupiter’s Temperature: 165K

Jupiter’s Atmosphere: 90% H2; 10% He.

Jupiter’s Largest Moons

Saturn’s Rings

Cassini Approaching Saturn

Saturn: The Elegant Planet

The Outer Planets

The most prominent feature of Saturn is its system of rings.

Features of Saturn• Saturn’s atmosphere is very active, with winds

roaring at up to 1500 kilometers per hour.• Large cyclonic “storms” similar to Jupiter’s Great

Red Spot, although smaller, occur in Saturn’s atmosphere.

Saturn: The Elegant Planet

The Outer Planets

Saturn’s Rings• Until the discovery that Jupiter, Uranus, and

Neptune have ring systems, this phenomenon was thought to be unique to Saturn.

• Most rings fall into one of two categories based on particle density.

Saturn’s Moons• Saturn’s satellite system consists of 31 moons.

• Titan is the largest moon, and it is bigger than Mercury.

Saturn: The Elegant Planet

The Outer Planets

Saturn’s Tilted Axis: 26.7°

Saturn’s Atmosphere: 96% H2; 3% He; 0.4% CH4

Saturn’s Temperature: 134K

Uranus

Uranus: The Sideways Planet

The Outer Planets

Instead of being generally perpendicular to the plane of its orbit like the other planets, Uranus’s axis of rotation lies nearly parallel with the plane of its orbit. Axis Tilt: 97.8°

Uranus’ atmosphere is 83% H2; 15% He; 2% CH4; .

Uranus’ temperature ranges from 49K to 76K, making it the coldest of the planets.

Neptune

Neptune: The Windy Planet

The Outer Planets

Winds exceeding 1000 kilometers per hour encircle Neptune, making it one of the windiest places in the solar system.

Neptune’s Tilted Axis: 28.3°

Neptune’s atmosphere: 80.0% H2; 19.0% He; 3.5% CH4.

Neptune’s Temperature: 60K to 70K

Pluto: Planet X

The Outer Planets

Pluto’s orbit is highly eccentric, causing it to occasionally travel inside the orbit of Neptune, where it resided from 1979 through February 1999.

Pluto’s Tilted Axis: 119.6°

Criterion for being a Planet.

What is a Planet?

A planet is: a body that orbits the Sun. A body massive enough for its own gravity to

make it round, A body that has “cleared its neighborhood” of

smaller objects around its orbit.

Criterion for being a Planet.

Sorry Pluto!

Under this new (2006) definition, Pluto, along with the other trans-Neptunian objects (like the even larger Eris discovered in 2005), does not qualify as a planet. The International Astronomical Union’s (IAU) decision has not resolved all controversies, and while many scientists have accepted the definition, some in the astronomical community have rejected it outright.

Asteroids: Microplanets

Minor Members of the Solar System

An asteroid is a small, rocky body whose diameter can range from a few hundred kilometers to less than a kilometer.

Most asteroids lie between the orbits of Mars and Jupiter. They have orbital periods of three to six years.

Irregular Orbits of Asteroids

Comets

Minor Members of the Solar System

Comets are small bodies made of rocky and metallic pieces held together by frozen gases. Comets generally revolve about the sun in elongated orbits.

Comets

Minor Members of the Solar System

Coma• A coma is the fuzzy, gaseous component of a

comet’s head.• A small glowing nucleus with a diameter of only

a few kilometers can sometimes be detected within a coma. As comets approach the sun, some, but not all, develop a tail that extends for millions of kilometers.

Comet’s Tail Points Away from the Sun

Comets

Minor Members of the Solar System

Kuiper Belt• Like the asteroids in the inner solar system, most

Kuiper belt comets move in nearly circular orbits that lie roughly in the same plane as the planets.

Oort Cloud• Comets with long orbital periods appear to be

distributed in all directions from the sun, forming a spherical shell around the solar system called the Oort cloud.

Comets

Minor Members of the Solar System

Halley’s Comet• The most famous short-period comet is Halley’s

comet. Its orbital period is 76 years.

Meteoroids

Minor Members of the Solar System

A meteor is the luminous phenomenon observed when a meteoroid enters Earth’s atmosphere and burns up, popularly called a shooting star.

A meteoroid is a small, solid particle that travels through space.

A meteorite is any portion of a meteoroid that reaches Earth’s surface.

Meteoroids

Minor Members of the Solar System

Most meteoroids originate from any one of the following three sources: (1) interplanetary debris that was not gravitationally swept up by the planets during the formation of the solar system, (2) material from the asteroid belt, or (3) the solid remains of comets that once traveled near Earth’s orbit.

Major Meteor Showers