The Solar System

• Section 1: An Overview of The Solar System• Section 2: The 9 Planets of The Solar System

Early views of the organization of Space were much different than ours.

Early astronomers believed that the Earth was the center of our Universe, and that the Earth was

surrounded by a ball, called a Celestial Sphere, on which were fixed most of the objects of the heavens.

This interpretation of our solar system is called a Geocentric Model, meaning Earth-centered.

Early astronomers noticed groups of stars that were visible at the same time every year. These were named

constellations, and were used as a basis for calendars.

The Orion Constellation

Astronomers noticed that some celestial bodies did change position relative to the constellations.

They called these “wandering stars” planets.

Notice the planet Mars moving across the constellations Gemini and Leo over the course of 11 months.

Astronomers also noted that, periodically, these planets which normally moved eastward, moved backward for a few weeks, then resumed their path eastward.

In 200 A.D., the Greek astronomer Ptolemy explained this “retrograde’ motion by stating that the planets

orbited the Earth in a circle, but also orbited another point in a circle, what he called an epicycle.

In the late 1400’s, the astronomer Copernicus proposed what was to become known as the

Heliocentric Model.

Copernicus stated that the Sun was the center of the Solar System, the Earth was a planet, and

that it orbited the Sun.

And, here is how he explained retrograde motion.

Mars retrograde motion Venus retrograde motion

In the 16th –century, the astronomer Johannes Kepler developed three laws to describe the way in

which planets move through Space.

Kepler’s 1st Law: Planets move through Space in an elliptical orbit, not a circular one. This causes the

distance from a planet to the Sun to vary.

Kepler’s 2nd Law: When a planet is closer to the Sun, it moves faster. (centrifugal

force and gravity at work!)

Kepler’s 3rd Law states that the further a planet is from the Sun the longer its period

of revolution (its year) will be.

In the 1600’s, Isaac Newton stated that a force called gravity was causing the planets to behave

as Kepler had observed.

He stated that all objects with mass exerted a force of attraction on other objects with mass, and that the

strength of that force is proportional to the mass of the objects and their distances from one another.

What’s in Our Solar System?

• Our Solar System consists of a central star (the Sun), the nine planets orbiting the sun, moons, asteroids, comets, meteors, interplanetary gas, dust, and all the “space” in between them.

• The nine planets of the Solar System are named for Greek and Roman Gods and Goddesses.

The Sun

• The Sun’s age is about 5 billion years. • Its energy comes from nuclear fusion (where hydrogen

is converted to helium) within its core. This energy is released from the Sun in the form of heat and light.

• Stars are the only solar bodies that generate their own light. Very bright planets, such as Venus and our moon, appear bright because they are reflecting sunlight. Remember: Stars produce light. Planets reflect light.

• Our sun is classified as a yellow main sequence star. A star’s temperature determines its “color.” The coldest stars are red. The hottest stars are blue.

The Relative Size of the Planets in the Solar System

Characteristics of Small Rocky Planets

• They are made up mostly of rock and metal.• They are very heavy.• They move slowly in space.• They have no rings and few moons (if any).• They have a diameter of less than 13,000 km

Mercury

• Mercury has a revolution period of 88 days. A revolution period is the time it takes for a planet to complete one full orbit around the sun. This is also called a year.

• Mercury has extreme temperature fluctuations, ranging from 800F (daytime) to -270F (nighttime).

• Even though it is the closest planet to the sun, recent radar info suggests there is ICE on Mercury! Scientists believe the ice is protected from the sun’s heat by crater shadows. It is covered with meteorite impacts and barely has a trace of an atmosphere.

Venus

• Venus is the brightest object in the sky after the sun and moon because its atmosphere reflects sunlight so well. People often mistake it for a star.

• The atmosphere of Venus has a large amount of carbon dioxide gas. Carbon dioxide traps heat in Venus’s atmosphere, causing the surface temperatures to increase greatly. We call this effect the Greenhouse Effect. Venus’s Greenhouse Effect is so strong that its maximum surface temperature may reach 900F.

• Venus has no moons. It has thick yellowish clouds composed of sulfuric acid driven by fast winds. Its surface is dry and dusty with craters, mountains, and volcanoes.

Earth• Earth is the only planet known to support living

organisms.• Earth’s surface is composed of 71% water.

– Water is necessary for life on Earth.– The oceans help maintain Earth’s stable temperatures.– Water is a primary cause of Earth’s surface weathering.

• Earth has a distinct atmosphere.– It helps screen harmful radiation from the sun.– It prevents meteorites from reaching Earth’s surface.– It traps heat to help maintain Earth’s stable temperatures.

• Earth has one moon.

Earth’s Moon• It takes the same amount of time for the moon to rotate

once on its axis as it does for it to orbit the earth (27.3 days). Thus, the same side of the moon always faces us.

• The moon’s surface is covered in dust and rocky debris from meteor impacts. It has no water or atmosphere. The dark areas of the moon are called Maria (Maria is a Latin word meaning “seas”). Maria are large craters which have been filled by solidified lava.

• The moon reflects light from the sun onto the earth’s surface. Sometimes the moon may appear reddish-brown in color as the sunlight is deflected through dust in the earth’s atmosphere.

• The moon’s gravitational effects on the earth are most apparent in the “coming” and “going” of the tides

• Mars has permanent ice caps at its poles. The ice caps are composed mostly of frozen carbon dioxide (what we call “dry ice”).

• Mars has the largest volcano in our solar system: Olympus Mons. Olympus Mons is approximately 24 km high (15 miles).

• Atmospheric dust makes Mars’s sky pink in color.

• Mars has two moons: Phobos and Deimos

Mars

Asteroid Belt

• Separates the Terrestrial planets from the Gas

• Composition of Asteroids– Rocky

Characteristics of Gas Giants

• They are made up mostly of gases (primarily hydrogen & helium).

• They are very light for their size.• They move quickly in space.• They have rings and many moons.• They have a diameter of less than

48,000 km

Jupiter• Jupiter is the largest and most massive planet: it’s

diameter is 11 times bigger than that of the Earth’s. Overall, Jupiter is about 318 times the size of Earth. Jupiter is composed almost entirely of hydrogen and helium.

• Because Jupiter rotates so quickly, it’s clouds form belts (low-lying, relatively warm cloud layers) and zones (bright, high-altitude, cooler cloud layers) that encircle the planet.

• Jupiter’s characteristic Great Red Spot is an enormous storm, consisting of a spiraling column of clouds big enough to contain three Earths. The clouds are colder than the surrounding areas, and so the Great Red Spot sits about five miles above the upper cloud layer.

• Jupiter has 16 known moons.

Saturn

• Saturn, like Jupiter, is composed almost entirely of hydrogen and helium. Saturn is the least dense of all the planets. In fact, Saturn’s density is less than that of water.

• Saturn has many rings composed primarily of ice with some ice-coated rocky particles. Saturn’s rings are very wide (they extend outward to about 260,000 miles from the surface) but very thin (less than 1 mile thick).

• Saturn has 18 known moons, some of which orbit inside the rings!

Uranus

• Uranus is tilted on its axis at 98. Because of its strongly tilted axis of rotation, Uranus essentially spins on its side as it orbits the sun.

• Uranus is blue in color due to methane gas in its atmosphere.

• Uranus has 11 dark rings surrounding it. These rings contain some of the darkest matter in our solar system.

• Uranus has 15 known moons, and scientists suspect more lurk within its rings.

Neptune

• Neptune has the fastest winds on the solar system: up to 2000 km/hr.

• Neptune is also blue in color due to methane gas in its atmosphere.

• Neptune has a Great Dark Spot in its atmosphere. The Great Dark Spot is a huge storm the size of Earth.

Pluto• Pluto is the only planet not visited by spacecraft. We

are not sure of its composition. Based on current data, scientists believe it is a small, rocky planet.

• Pluto seems to lie on its side: its equator points straight up, and one of its poles points directly at the sun.

• Pluto has only one moon (Charon). Pluto’s moon is half the size of Pluto itself, which is unusually large for a moon. Because they are so close in size, sometimes Pluto and its moon are considered to be a double planet system.

• Pluto was located and named in 1930.

Neither Gas or Rocky Planet

Comets• Comets are small rock,

dust and ice objects that orbit the Sun.

• As the comet approaches the Sun, the ices in the nucleus sublime to form the coma, a dense cloud of gas and dust particles around the nucleus. The coma contains water, carbon dioxide and other neutral gases.

Comet Tail direction• When comets are near

the Sun, the pressure of the Sun's radiation on the coma blows the dust and gas in the coma back into a long tail or tails.

• Due to the Solar winds the

tail always points away from the sun. This means as the comet orbits back into deep space the tail will be leading it.

Asteroidscomplex mixtures of metals, and carbon and silicon compounds, asteroids are not just dull grey lumps of cratered rock

METEOROIDS, METEORS, METEORITES

• Meteoroids – is a rock or icy fragment traveling inspace. (much smaller than asteroids • Meteors – this is what a meteoroid is called when it enters into Earth’s atmosphere. Also called a shooting star.Meteorite – is the part of a meteoroid that has survived its trip through the atmosphere and strikes Earth’s surface.

Meteorite Types

Iron primarily iron and nickel; similar to type M asteroids

Stony Iron mixtures of iron and stony material like type S asteroids

Chondriteby far the largest number of meteorites fall into this class; similar in composition to the mantles and crusts of the terrestrial planets

Carbonaceous Chondrite

very similar in composition to the Sun less volatiles; similar to type C asteroids

Achondritesimilar to terrestrial basalts; the meteorites believed to have originated on the Moon and Mars are achondrites

Solar Eclipse

Tides