2.3 THE SOLAR SYSTEM

Formation of the Solar System• In space, a cloud of gas and interstellar dust is

known as a nebula.– Often consists of 92% Hydrogen (H), 7% Helium

(He), and less than 1% of remaining heavier elements.

• These clouds rotate, contract gravitationally, and spin rather quickly.

Formation of the Solar System• Studies of these nebulae have led to a theory

concerning the beginning of our solar system.

• According to the Solar Nebula Theory, the Sun and planets formed from a rotating disk of dust and gases.

Also known as the Solar Nebula Disk Model (SNDM).

As speed increased, the center flattened out and matter became more concentrated until the Sun eventually formed.

Formation of the Solar System• The planets began their formation through a

process known as accretion, where solid bits of matter collide and form together.– This colliding matter formed small, irregular

shaped bodies known as planetesimals.

– Inner planets (Terrestrial): Mercury, Venus, Earth, and Mars.• Relatively small, rocky, and dense.• Contain large percentages of heavy elements such as

iron (Fe) and nickel (Ni).

– Outer planets (Jovian): Jupiter, Saturn, Uranus, and Neptune.• Huge gas giants with relatively low densities.• Colder planets, having mainly light elements:

hydrogen (H) and helium (He) gases.

Planetary Data

Terrestrial Planets

Mercury: The Innermost Planet• Innermost and smallest planet.

– NASA’s Messenger provides many images.

• Absorbs most sunlight striking its surface due to the lack of an atmosphere (similar to Earth’s moon).

• Exhibits cratered highlands, like our moon, and smooth terrains resembling maria of the moon.

• Unlike the moon, Mercury is very dense implying it likely has a large iron core.

• Greatest temperature extremes of any planet (slow rotation: 59 Earth days).

Venus: The Veiled Planet• Similar to Earth in size, density, mass,

and location in the solar system thus commonly referred to as “Earth’s Twin”.– Covered in thick clouds, hiding the

surface of the planet.

• Volcanism and tectonic activity are believed to have impacted the surface (few impact craters, similar to Earth).

• 80% of its surface is covered with volcanic flows.

Venus: The Veiled Planet• Radar-generated image of a large volcano on the

surface.– Magellan spacecraft data.

• Greenhouse Effect: the trapping of heat due to certain atmospheric gases.– On Venus, this effect has heated the planet to extreme temperatures;

hottest planet in the solar system.

• Atmosphere is 97% carbon dioxide (CO2), which is a greenhouse gas.

• Lacks oceans, which could dissolve CO2, removing it from the atmosphere.

– Responsible for the hot temperatures on the planet.

Mars: The Red Planet• The most pronounced feature of

Mars is its white polar ice caps.– Data collected from probes concluded

the ice caps are made of water ice, covered by frozen carbon dioxide.

• Dust storms occur on the planet and much of the surface resembles a large desert.

• Atmospheric composition similar to that of Venus.

– Atmosphere is extremely thin and doesn’t trap heat like the atmosphere of Venus does, resulting in very cold temperatures on the planet.

Mars: The Red Planet

• Also has several large inactive volcanoes, including the largest known in the solar system, Olympus Mons.– 3 times the elevation of Mt.

Everest (approx. 90,000 ft.)

• Several canyons are present as well, some even larger than Earth’s Grand Canyon.– Largest is the Valles Marineris, which is

more than 5000 km. long and 8 km. deep.

Mars: The Red Planet• Some areas of Mars exhibit drainage patterns,

quite similar to those created by streams and rivers on Earth.

• Evaporite minerals have been found, as well as geologic formations associated with liquid water. – Present Martian atmosphere contains only slight

traces of water.

• Some scientists believe the stream-like valleys were created due to melting of ice along the polar ice caps.– Others believe Mars was once covered in flowing

water.

• Since water is essential to life, this exploration will continue for years to come.

Jovian Planets

Jupiter: Giant Among Planets• Largest planet of our solar system.

– Mass is over 300 times Earth’s mass.

• Hydrogen (H) and Helium (He) make up 92% of Jupiter much like our Sun.

• “Star That Failed”– Not enough mass to allow nuclear fusion

to begin in its core.

• Alternating light and dark bands are gases, such as ammonia (NH3) and methane (CH4) swirling around the planet at a quick pace.– Fastest rotation period of any planet

• 9 hours, 50 minutes.

VOYAGER 1Video data from approach to Jupiter in 1979

Jupiter: Giant Among Planets• Jupiter’s most distinctive feature is

its Great Red Spot.

– Giant rotating storm, similar to a hurricane on Earth (trace amounts of water present deep within the atmosphere).

– Twice the size of Earth.

• Several other smaller storms have been observed on Jupiter.

• High wind speeds are caused by temperature differences from heat within the planet’s interior (liquid hydrogen pressure).

Saturn: The Elegant Planet• Composition similar to Jupiter’s.

• Voyager 1 and 2 spacecrafts collected various data.

• Least dense (lightest) planet of the solar system.

• Known for its rings, which are twice the planet’s diameter.

– All the gas giants have faint rings, however, Saturn has the most complex and extensive ring system.

– Made of billions of dust and ice particles.

– Probably came from comets and other bodies traveling in space.

Uranus: The Sideways Planets• Unique orientation of the planet

wasn’t discovered until 1986, when the Voyager 2 spacecraft passed by.

• The planet is turned on its side.– Axis almost parallel to its plane of

orbit.

• Similar atmospheric composition to the other gas giants.– Blue-green color of the planet also

shows a significant amount of methane (CH4) gas present.

Neptune: The Windy Planet• Neptune was named after the

Roman God of the sea.

• Voyager 1 and 2 also provided images of Neptune.

• Dark blue-green planet due to its composition (H2, He, CH4).

• Strongest known winds in the solar system.

• The Great Dark Spot of Neptune is similar to Jupiter’s Great Red Spot, but not quite as large.

Objects Beyond Neptune• Pluto was discovered in 1930 and up until 2006, it was considered the

9th planet of our solar system.

• It is now characterized as a dwarf planet, which is defined by meeting the following criteria:

1. An object orbiting the Sun2. Is round because of its own gravity3. Has not cleared the region around its orbit4. Is not a satellite of another planet

Objects Beyond Neptune• In recent years, astronomers have discovered hundreds of

objects beyond Neptune’s orbit and have termed them Trans-Neptunian Objects (TNO’s).

• Most are just small chunks of ice.

• TNO’s exist in a region known as the Kuiper Belt.

Satellites of Other Planets

• Until the 1600’s, astronomers believed Earth was the only planet with a moon.

• In 1610 Galileo discovered four major moons of the planet, Jupiter.

• Since then, astronomers have discovered all planets within our solar system, with the exception of Mercury and Venus, have moons.

Moons of Mars• Mars has 2 known moons,

named Phobos and Deimos.

• Irregularly-shaped chunks of rock and are thought to be captured asteroids.

• Surfaces are dark, like the maria of the moon.

• Exhibit several craters, indicating possible asteroid contact and old age. Deimos

Phobos

Moons of Jupiter• Jupiter has 63 known moons, including the

largest 4, known as the Galilean Moons:

IO

EUROPAGANYMEDECALLISTO

Io• Io is the innermost of Jupiter’s 4 major Galilean moons.

• Several hundred active volcanoes exist on the surface.– Eject thousands of metric tons of material each second.

– Most volcanic material is believed to be mainly sulfuric, due to the yellowish color of Io.

Europa• Europa is about the size of Earth’s

moon and is slightly less dense than our moon.

• Crust of ice covers the moon; believed to be about 100 km. in thickness.

• Scientists believe a flowing ocean of liquid water may exist underneath this ice sheet.

– If liquid water exists, simple life forms may exist as well.

– Studies continue to this day of life potential on Europa.

http://www.youtube.com/watch?v=6Nz9TdNVz0w

Ganymede• Ganymede is the largest known

moon of the solar system.– Larger than the planet Mercury.

• Much of the surface is covered with ridges and valleys.

• A magnetic field is believed to be in existence around Ganymede.– Only moon in the solar system

known to have its own magnetic field.

– Surrounded by Jupiter’s much more powerful magnetic field.

Callisto• Callisto is similar to Ganymede in size, density, and composition,

but has a much rougher surface.

• One of the most densely cratered moons within our solar system.

– Craters are the result of collisions from asteroids occurring early in the history of our solar system.

Moons of Saturn• Saturn has 31 known moons,

most of which are small, icy bodies with many craters.

• Saturn’s largest moon is Titan, which is the 2nd largest moon in the solar system, next to Jupiter’s Ganymede.

• Titan has a thick atmosphere, composed mainly of Nitrogen (N).

Moons of Uranus and Neptune

• Uranus has 25 known moons, the most interesting being Miranda. – Originally believed to be split apart by

asteroid impact then joined back together (process of accretion).

– Further studies suggest tectonic activity does exist, causing the distorted appearance.

• Neptune has 13 known moons, the largest being Triton.– Revolves around Neptune in a backwards,

or retrograde, orbit (clockwise).

Miranda

Triton

Pluto’s Moons• Although no longer considered a planet, Pluto does have at least three

known moons.

• The largest moon, Charon, is almost half the size of Pluto itself.

– Exhibits synchronous rotation, just like Earth’s moon.

• Pluto’s other two moon, Nix and Hydra, are much smaller.

– Both were discovered in 2005 by the Hubble Space Telescope.Charon

Asteroids• Asteroids are fragments of rock

orbiting the Sun; largest minor bodies of the solar system.

– More than 300,000 have been discovered.

• Largest known is Ceres.

– Exists within the Asteroid Belt between Mars and Jupiter.

– Also considered a dwarf planet.

• Composition can vary from Carbon (C), Iron (Fe), Nickel (Ni) and Silicon (Si) materials.

Ceres

Comets• Small bodies of ice, rock, and cosmic dust

following a highly elliptical orbit around the Sun are known as comets.

– Most famous is Halley’s Comet, which passes by Earth every 76 years.

– Most recent 1986; Next return in 2061.

• Core (Nucleus): made of rock, metals, and ice.

• Coma: cloud of gas and dust surrounding the core.

• Tail: electrically charged gas particles (ions) resulting from sunlight changing the comet’s ice into gas (sublimation).

Oort Cloud

• Most astronomers think comets originate in a spherical cloud of dust and ice surrounding out solar system known as the Oort Cloud.

• Believed matter within this cloud was leftover from the time the solar nebula was formed.

– Contains the nuclei of billions of comets.

Meteoroids, Meteors, and Meteorites• Smaller particles, possibly

coming from asteroids or comets, orbiting the Sun are known as meteoroids.

– Most have diameter < 1 mm.

• When a meteoroid enters Earth’s atmosphere, friction heats the surface and causes it to burn up.

– As it burns it produces a bright streak of light known as a meteor, which is commonly referred to as a “shooting star”.

• Any part of a meteoroid making contact with Earth’s surface, is known as a meteorite.

Meteoroid

Meteor

Meteorite