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Our Solar System
Our Solar System: The Planets
• The Sun is at the center of our Solar System.
• The Sun makes up 99.85% of the mass of the solar system.
The Planets: An Overview
The Solar System
The terrestrial planets are planets that are small and rocky—Mercury, Venus, Earth, and Mars.
The Jovian planets are the huge gas giants—Jupiter, Saturn, Uranus, and Neptune.
Pluto does not fit into either the Jovian or the terrestrial category.
Terrestrial Planets
MercuryVenus Earth
Mars
Jovian Planets
Jupiter SaturnUranus Neptune
• The terrestrial planets are also called the Rocky or the Inner planets.
• The Jovian planets are also called the Giant or the Outer or the Gas planets.
Orbits of the Planets
The Sun’s gravitational pull guides the elliptical orbits of the planets in our Solar System.
The Planets: An Overview
The Solar System
Size is the most obvious difference between the terrestrial and Jovian planets. Earth’s mass is 1/17th of the mass of
Neptune (the smallest Jovian planet).
Density, chemical makeup, and rate of rotation are other ways in which the two groups of planets differ.
Planetary Data
Interior Planetery Composition
•The planets are made of three different substances: gases, rocks, and ices.
•Gases (hydrogen and helium) are those with melting points near absolute zero (-273⁰ C).
•Rocks are mostly silicates (silicon and oxygen) and metallic iron which have melting points above 700 ⁰ C.
• Ices are ammonia (NH3), methane (CH4), carbon dioxide (CO2) and water (H2O) which have intermediate melting points.
The terrestrial planets are dense with mostly metallic and rocky substances.
The Jovian planets are less dense with large amounts of gases 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 thin, meager atmospheres at best.
• Gases can escape from its planet’s gravity if it reaches escape velocity.
• For Earth, escape velocity is 11 km/s.
• For Jovian planets, the escape velocities are between 21-60 km/s. So it is more difficult for gases to escape a Jovian planet’s gravity.
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.• A nebula often consists of 92% H, 7% He,
and <1% heavier elements.
• According to the nebular theory, the sun and planets formed from a rotating disk of dust and gases.
• As the speed of rotation increased, the center of the disk began to flatten out and become more concentrated. This eventually became our sun!!
Nebula
The Hubble Telescope captured this picture of a nebula near a dying star (450 light years away in the constellation Aquarius) (these are two gases colliding)
Formation!
• The Solar System was formed from the contraction of a pre-solar nebula, a vast cloud of gas and dust.
• The center of the nebula became the Sun and the outer parts accreted to form the planetesimals.
Formation of the Solar System
The Solar System
• Planetesimals are small, irregularly shaped bodies formed by colliding matter.
• Over time, these planetisimals will collect enough material/mass to have their own gravitational pull.
• The inner planets (close to the sun) were too hot for ice to form and only rocky material accreted.
• The outer planets (far from the sun) had both solid matter and ice to accrete.
Formation of the Universe
Planetary Composition, Distance from the Sun, and Melting Point
Mercury: The Innermost Planet
The Terrestrial Planets
• Mercury is the innermost and second smallest planet; it is hardly larger than Earth’s moon.
• Because Mercury is so small, the gravity on Mercury is 38% of the gravity on Earth.
• A 100 pound person would weigh only 38 pounds on Mercury. To calculate your weight on Mercury, just multiply your weight by 0.38
Orbit: very elliptical with no seasons (because no tilt)
Mercury orbits the sun every 88 days and has a rotation of 59 days.
Surface Features
• Mercury has cratered highlands, much like the moon, and vast smooth terrains that resemble maria.
Surface Temperatures• Mercury has a very, very thin atmosphere.
• This means that it has no shielding from the sun’s energy (on the light side) and no way to hold this energy (on the dark side).
• Mercury has the greatest temperature extremes of any planet.
• Since the atmosphere is so thin, the sky would appear pitch black (except for the sun, stars, and other planets, when visible), even during the day.
• Mercury has a daytime temperature of about 400⁰ C and a nighttime temperature of about -200 ⁰ C, a mere 73 degrees above absolute zero.
Mercury’s Surface
If you were on the surface of Mercury, the Sun would look almost three times as big as it does from Earth!
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: The Veiled Planet
The Terrestrial Planets
Venus
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
Surface Features
• Venus is covered in thick clouds that visible light cannot penetrate.
• About 80 percent of Venus’s surface consists of plains covered by volcanic flow.
Venus’ Surface
Venus’ Atmosphere
• Venus has the densest atmosphere (93 times denser than Earth’s) of all the terrestrial planets, consisting mostly of carbon dioxide (97%).
• Venus is covered with an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light.
Revolution and Rotation
• Venus’ orbital length is 224.7 Earth days.
• Venus’ rotational period is 243 Earth days (slowest of any major planet).
• Also, Venus is the only planet to rotate clockwise!!!
Surface Temperatures
The average surface temperature of Venus reaches 475oC. There is little variation between night and day because of the thick atmosphere and slow rotation.
There is minimal tilt so essentially no seasons.
Mariner 10 Images
Mars (taken by the Hubble)
Mars is the Red Planet because of the iron oxide in the crust . Iron oxide is reddish in color.
Mars: The Red Planet!
The Martian Atmosphere
• The Martian atmosphere has only 1 percent of the density of Earth’s.
• Although the atmosphere of Mars is very thin, extensive dust storms occur and may cause the color changes observed from Earth.
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.
Mars’ Moons
• Mars has two moons, Phobos and Deimos, which are small and irregularly shaped.
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.
Mars
• The Polar Landers have determine water on Mars!!!
Water on Mars
Jupiter: Giant Among Planets
23.3 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 and the Great Red Spot
Jupiter: Giant Among Planets
23.3 The Outer Planets
• Jupiter’s satellite system, including the 28 moons 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’s Largest Moons
Saturn: The Elegant Planet
23.3 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.
Cassini Approaching Saturn
Saturn: The Elegant Planet
23.3 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’s Rings
Uranus: The Sideways Planet
23.3 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.
Uranus
Neptune: The Windy Planet
23.3 The Outer Planets
Winds exceeding 1000 kilometers per hour encircle Neptune, making it one of the windiest places in the solar system.
Neptune
Pluto: Planet X
23.3 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.
Asteroids: Microplanets
23.4 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
23.4 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
23.4 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
23.4 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
23.4 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
23.4 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
23.4 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
