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. (mass sun = 2.0 x kg)  The Sun is 70% H 2 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 Mercury Venus Earth Mars

Jovian Planets Jupiter Saturn Uranus 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% O 2 ; 29% Na; 22% H 2 ; 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.)NASA's Mariner 10 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% CO 2 ; 3.5% N 2.

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% CO 2 ; 2.7% N 2 ; 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

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% H 2 ; 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% H 2 ; 3% He; 0.4% CH 4  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% H 2 ; 15% He; 2% CH 4 ;.  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% H 2 ; 19.0% He; 3.5% CH 4.  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  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