Chapter 23: Touring Our Solar System

The Sun The Sun is the center of our solar system. The Sun makes up 99.85% of all the mass of our solar system. The Sun’s gravitational force holds the planets in their orbits around the Sun.

The Planets: An Overview Terrestrial (Earth-like) Planets – Mercury, Venus, Earth, and Mars are relatively small and rocky. Jovian (Jupiter-like) Planets – Jupiter, Saturn, Uranus, and Neptune are huge gas giants. Differences between the Terrestrial and Jovian planets include size, density, chemical makeup, and rate of rotation. The Terrestrial planets are dense, consisting mostly of rock and metallic substances, and only minor amounts of gas and ices. Jovian planets are less dense and contain large amounts of gases and ices.

Formation of the Solar System Nebula – a cloud of dust and gas in space. Nebular Theory – the sun and the planets formed from a rotating disk of dust and gases. Planetesimals – solid bits of matter collided and clumped together through a process called accretion forming small, irregular shaped bodies.

Nebular Theory

Section 23.2 The Terrestrial Planets Mercury

Mercury Planet closest to the sun. Smallest planet in the solar system. Has an orbit period of 88 days. The shortest of any planet. Takes 59 days to rotate once on its axis. Temperature may reach as high as 427oC (800.6oF) during the day (hot enough to melt lead) and plunge to -173oC (-279.4oF) at night. Mercury has the greatest temperature extremes of any planet.

Venus

Venus Second planet from the sun called Earth’s twin. Orbit period of 225 days. Rotates once on its axis every 244 days! Rotates the opposite of all the other planets. The Sun rises in the west and sets in the east. Average surface temperature is 462oC (863.6oF) making it the hottest planet. Atmospheric pressure is about 90 times that of Earth. Venus’s atmosphere is 97% carbon dioxide.

Earth

Earth Our planet, the third planet from the sun. Orbit period is 365.24 days. Completes one rotation in 23 hours and 56 minutes. Only known planet with liquid water. Average surface temperature of 14oC (~59oF) Only planet known to support life.

Mars

Mars

Mars Fourth planet from the sun. Orbit period of 687 days. Rotates on its axis once in 24 hours 37 minutes. Mars has seasons like Earth. Mars has two moons, Phobos and Deimos Mars has the largest known volcano in the solar system, Olympus Mons, which is three times higher than Mt. Everest. Mars also has the largest canyon, Valles Marineris, which is as long as the United States.

Mars Evidence has been found on Mars of erosion by liquid water. Water is frozen in the Martian soil and icecaps. Temperatures range from 20oC (~68oF) in the summer to -130oC (~ -200oF) in the winter.

Section 23.3 The Outer Planets (and Pluto)

Jupiter

Jupiter Fifth planet from the sun. By far the largest of all planets. Its mass is 2.5 times greater than all of the other planets and moons combined! Orbit period is about 12 years, but it rotates faster than any other planet – once every 9 hrs and 50 minutes! Jupiter has at least 50 moons and counting! The 4 largest moons, Europa, Io, Ganymede, and Callisto, are called the Galilean moons, because they were discovered by Galileo.

Jupiter Temperatures in the interior of Jupiter may raise as high as 30,000oC (~54,000oF) It is composed of mostly hydrogen and helium, much like that of the sun, but Jupiter was not massive enough for nuclear fusion to begin. The Great Red Spot on Jupiter is a giant rotating storm in the atmosphere that has been raging for several hundred years. Wind speeds reach as high as 540 km/hr.

Saturn

Saturn Sixth planet from the sun. The second largest planet. Average temperature is -176oC (~ -285oF). Has at least 53 moons and 9 provisional moons and an immense, complex ring system. Orbit period of 29.5 years Rotates once every 10 hrs and 30 minutes The least dense planet in the solar system. It would float in water!! Its largest moon is Titan, which is larger than Mercury and has an atmosphere.

Uranus

Uranus Seventh planet from the sun Discovered in 1781. Orbit period of 83.8 years Has at least 27 moons and at least 9 small rings. The only planet in the solar system that rotates horizontal to its plane of orbit, like a rolling ball! Rotates once in 17hr 14min Average surface temperature is about -214oC (~ -350oF)

Neptune

Neptune Eighth planet from the sun. Orbit period of 163.7 years Rotates once in 16 hrs 07 min Neptune has 13 moons and possibly 4 rings The largest of these moons is Triton. The upper atmosphere is composed of white clouds of frozen methane. Has an Earth sized storm called the Great Dark Spot with winds exceeding 1,000 km/hr. Average surface temperature is about -225oC (~ -373oF).

Pluto

Pluto: Dwarf Planet Pluto has actually been recently removed from the list of planets. Ninth “planet” from the sun discovered in 1930. Clyde Tombaugh discovered Pluto by accident. Orbit period is 248.6 years Rotates once every 6.4 days Has one large moon called Charon. Average surface temperature of -236oC

Dwarf Planets Along with Pluto, there are 4 other dwarf planets: Eris, Ceres, Haumea, and Makemake.

Dwarf Planets

Section 23.4 Minor Members of the Solar System

Asteroids Asteroid – small rocky bodies that have been likened to “flying mountains” Most asteroids lie between the orbits of Mars and Jupiter. They have orbital periods of 3 to 6 years. Some have very eccentric orbits, a few regularly pass Earth and our moon Many asteroids have irregular shapes, and some planetary geologists believe the asteroids are fragments of a broken planet (pulled apart by the immense gravity of Jupiter)

Asteroids

Orbits of Asteroids

Known Impacts on Earth

Comets

Comets Comets – pieces of rocky and metallic materials held together by frozen gases Most comets travel in elongated orbits, taking them past Pluto and take hundreds of thousands of years to go around the sun. Coma – glowing head of a comet, caused by the solar energy vaporizing frozen gases 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 develop a tail that extends for millions of kilometers. The tail of the comet always points away from the sun, this is accounted for by the solar wind and radiation pressure

Comet Origins Kuiper Belt – where most short-period comets are thought to originate from, it is a belt of material orbiting outside the orbit of Neptune. Oort Cloud – Unlike the Kuiper Belt comets, these comets have longer orbital periods and aren’t confined to the plane of the solar system. The Oort Cloud appears as a spherical shell of comets and other materials surrounding our solar system.

Comet Origins

A Comet’s Tail Always Points Away from the Sun

Meteoroids Meteoroid – a small solid particle that travels through space Most meteoroids originate from any one of the following sources: (1) interplanetary debris that was not gravitationally swept up 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 Meteor – meteoroids that enter Earth’s atmosphere and burn up, a “shooting star” The light that we see is caused by the friction between the meteor and the air Meteorite – a meteoroid that reaches Earth’s surface A few meteorites have blasted out craters on Earth’s surface

Meteoroids, Meteors, Meteorites

Dates of Meteor Showers

Meteorites and the Age of the Solar System How did scientists determine the age of the Solar System? They use radiometric dating to determine that the oldest meteorites found on Earth formed more than 4.54 billion years ago Scientists believe that the composition of these meteorites is similar to the composition of other materials in the inner solar system during its formation The oldest moon rocks are believed to be ~4.5 billion years old The oldest known Earth rocks are found in Canada ~4 billion years old