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Exploring the Solar System

Middle School ScienceMrs. Dainty

The Inner Planets

Key Terms Terrestrial planets Mercury Mars Venus Earth Greenhouse effect

Key Concepts What do the inner planets have in common? What are the main characteristics that

distinguish each of the inner planets? What are scientists doing today to investigate and

explore the inner planets?

The inner planets are: Mercury, Venus, Mars, and Earth.

These four planets are more similar to each other than they are to the outer planets.

They are small. They are dense. They have rocky surfaces. Often called the terrestrial planets. (Terra

= “earth” in Latin.)

The Inner Planets - Introduction

Earth has three main layers: a core, mantle, crust. The core is made of dense iron and nickel. Earth is unique in our solar system in having

liquid water at its surface. (70% of surface!) Water can exist as solid, liquid, or gas. Earth has enough gravity to hold on to most

gases. The atmosphere extends for 100km above surface.

Most of atmosphere is Nitrogen. Oxygen makes up about 20% of atmosphere.

Earth Atmosphere & Water

Mercury is the smallest terrestrial planet and the planet closest to the sun.

Not much larger than Earth’s moon. Mercury has no moons of its own. Interior probably made of the dense

metal iron. It is hard to see since it is so close to

the sun.

Mercury

The Mariner 10 is a probe that flew by Mercury three times in 1974 and 1975.

From this probe, we learned that Mercury has many flat plains and craters on its surface.

The surface has changed little in billions of years.

Mercury

{ {The Mariner 10 Probe The Surface of Mercury

Mercury Images

NASA is beginning new missions to Mercury. On March 17th, the spacecraft MESSENGER successfully orbited the planet for the first time ever!

On May 10th of this year, NASA will hold a press conference to describe their early scientific findings of Mercury.

Mercury Exploration in 2011

MESSENGER spacecraft orbits Mercury!

Mercury has virtually no atmosphere. Daytime temps are very high, so gas

particles move very fast. Mercury’s mass is small, so gravity is

weak. Fast-moving gas particles can easily

escape into space. Mercury is a planet of extremes, and has a

greater temperature range than any other planet. Daytime temps get up to 430˚C. Because there’s no atmosphere, at night heat escapes into space. Temps drop to -170˚C.

Mercury’s Atmosphere

Venus can sometimes be seen in the west just after sunset. It is known as the “evening star” even though it isn’t a star at all!

When it’s visible in the morning before the sun rises its known as the “morning star.”

Space missions to Venus have shown us the surface is covered in craters, mountains, volcanoes, and lava plains.

Venus is similar in size, mass, and internal structure to Earth, so it’s sometimes called “Earth’s twin.” However, they are very different in other ways!

Venus

Venus From Space

It takes Venus about 7.5 Earth months to revolve around the sun. It takes about 8 months for Venus rotate once on it’s axis.

That means that Venus rotates so slowly that one “day” is longer than one “year” there!

Venus oddly enough rotates from east to west, the opposite direction from most other planets and moons.

Astronomers think its because a very large object struck Venus billions of years ago, and the collision caused Venus to change directions. Or, perhaps it’s due to Venus’s thick atmosphere.

Venus’s Rotation

Venus’s atmosphere is so thick it is always cloudy there. The clouds are made mostly of droplets of sulfuric acid.

If you could stand on the surface, you would be crushed by the weight of its atmosphere. The pressure of atmosphere is 90 times greater than that of Earth’s.

Atmosphere is mostly made of carbon dioxide, so you wouldn’t be able to breathe there.

Venus’s Atmosphere

Venus is closer to the sun than the Earth, so it receives more solar radiation.

Much of it is reflected by the atmosphere. However, some reaches the surface and is

later given off as heat. Carbon dioxide traps the heat, causing

Venus to have the hottest surface temperature of any planet. (460˚C!) It’s hot enough to melt lead.

This trapping of heat by the atmosphere is called the greenhouse effect.

Venus’s Atmosphere Cntd.

Greenhouse Effect on Earth & Venus

Mars

Mars is called “the red planet.”

When you see it in the sky, it has a slightly reddish tinge due to the breakdown of iron-rich rocks, which creates a rusty dust that covers much of Mars’s surface.

If you could stand on the surface, you would see rocks and boulders covered in red dust.

The atmosphere of Mars is more than 90% carbon dioxide.

Similar in composition to Venus’ but thinner. You could walk around on Mars, but you’d have

to wear an airtight suit and carry your own oxygen. (Like a scuba-diver!)

Mars has few clouds, thin compared to Earth’s. Because Mars has a transparent atmosphere we

can view the surface of Mars with a telescope. Temps on the surface range from -140˚C to

20˚C

Mars’s Atmosphere

In 1877, Giovanni Schiaparelli announced that he had seen long, straight lines on Mars.

In the 1890s and 1900s, Percival Lowell convinced many people these channels were build by intelligent Martians to carry water.

Astronomers now know Lowell was mistaken; there are not canals on Mars.

Water on Mars

Images of mars do show a variety of features that look like they were made by ancient streams, lakes, or floods.

There are huge canyons and features that look like the remains of ancient coastlines.

Scientists think that large amounts of liquid water flowed on Mars’s surface in the distant plants. (They think Mars much have been warmer and had a thicker atmosphere at the time.)

Water on Mars cntd.

Melas Chasma on Mars

The photo shows the Melas Chasma on Mars, which reaches a depth of 5.6 miles; it’s part of the staggering the Valles Marineris rift valley, which stretches almost 2,500 miles across the surface of the red planet.

(For comparison’s sake, our earthly Grand Canyon is 1.1 miles deep and 277 miles long.)

At present, liquid water cannot exist on the surface of Mars for long. The atmosphere is so thin that liquid quickly turns into gas because of radiation from the sun.

Mars’s water is now located at two polar ice caps, which consist of frozen water and carbon dioxide.

Some exists as water vapor in the atmosphere, and some of that may have escaped into space.

Scientists think that there must be a large amount of water frozen underground.

Water on Mars cntd.

Northern Ice Cap of Mars

Mars has a tilted axis as Earth does, so it experiences seasons.

During the Martian winter, the ice cap grows larger as a layer of frozen CO2 covers it.

Windstorms arise as seasons change, blowing dust around.

Seasons on Mars

Many space probes have visited Mars. In 2004, NASA’s Spirit and Opportunity rovers

explored opposite sides of the planet. They examined rock and soil samples. At both locations, they found evidence that liquid water was once present.

NASA’s Mars Odyssey has been orbiting Mars since 2001! The Odyssey is monitoring season changes and making detailed maps of the planet.

Exploring Mars

 In 2002, the Odyssey detected hydrogen just below the surface throughout Mars' high-latitude regions.

“The deduction that the hydrogen is in frozen water prompted NASA's Phoenix Mars Lander mission, which confirmed the theory in 2008.

Odyssey also carried the first experiment sent to Mars specifically to prepare for human missions, and found radiation levels around the planet from solar flares and cosmic rays are two to three times higher than around Earth. ”

Exploring Mars Cntd.

“Odyssey will support the 2012 landing of the Mars Science Laboratory (MSL) and surface operations of that mission. MSL will assess whether its landing area has had environmental conditions favorable for microbial life and preserving evidence about whether life has existed there. The rover will carry the largest, most advanced set of instruments for scientific studies ever sent to the Martian surface. ”

(Quotations taken from NASA release on Dec. 10, 2010. See NASA.gov.)

Exploring Mars Cntd.

Mars Exploration Cntd.

For most of this month (March 2011) the rover Curiosity is in a sealed chamber that will simulate conditions on March in preparation for the landing of the MSL.

The Curiosity is scheduled to launch in the fall of 2011 and land on Mars in August of 2012.

Volcanoes on Mars

There are regions of Mars that have giant volcanoes.

Astronomers see evidence that lava flowed from the volcanoes in the past, but they are no longer active.

Olympus Mons on Mars is the largest volcano in the solar system. It is about three times as tall as Mount Everest – the tallest mountain on Earth!

Mars’s Moons

Mars has two very small moons: Phobos and Deimos.

Phobos is closer than Deimos.

Phobos is slowly spiraling towards Mars, and scientists predict it will smash into Mars in 40 million years.

They are covered with craters like Earth’s moons.

List the four inner planets in order of size, from smallest to largest.

How are the four inner planets similar? Describe an important characteristic of

each inner planet. Compare and contrast the atmospheres

of the four inner planets. Why are the average temps on Venus

much higher than those of Mercury even though Mercury is closer to the sun?

Review Questions

The Outer Planets

{ {Key Terms

Gas Giant Ring Jupiter Saturn Uranus Neptune Pluto Dwarf Planet Asteroid Belt

Key Concepts

What characteristics do the gas giants have in common?

What characteristics distinguish each of the outer planets?

How is Pluto different from the gas giants?

How are dwarf planets different from planets?Key Terms and

Concepts

Introduction to the Outer Planets

There are four outer planets: Jupiter, Saturn, Uranus, and Neptune. They are called the gas giants.

These four planets are much larger and more massive than Earth (see picture of earth vs. Jupiter)

They do NOT have solid surfaces.

Pluto is now called a “dwarf planet” though it was classified as a planet previously. It is small and rocky like the terrestrial planets.

The four gas giants are composed mainly of hydrogen and helium. (Like the sun!)

Because they are so massive, they exert a strong gravitational force. This gravity keeps their gases from escaping, so they have thick atmospheres.

Much of the H and He is in liquid form because of the enormous pressure inside the planets.

Because they are so far from the sun, the outer layers of the gas giants are very cold. Temperatures inside the planets increase greatly.

All gas giants have many moons. Each is surrounded by a set of rings. Rings are

thin disks of small particles of ice and rock.

Introduction to the Gas Giants

Jupiter

Jupiter is the largest and most massive planet!

Atmosphere Thick atmosphere of H and He. There is a Giant Red Spot, a storm larger than

Earth. The storm’s swirling winds blow hundreds of km per hour, similar to a hurricane but without land to weaken it

The weather on Jupiter is caused by the Sun’s heat and Jupiter’s internal gravity.

Jupiter

{ {Diagram of Internal Structure Jupiter’s Structure

Astronomers think Jupiter probably has a dense core of rock and iron at its center. The core is 10 times the size of Earth.

A thick mantle of liquid H and He surrounds the core.

Above the liquid is the gaseous atmosphere.

The pressure at the core of Jupiter is 30 million times greater than pressure at Earth’s surface due to the crushing weight of Jupiter’s atmosphere.Jupiter’s Internal

Structure

Jupiter’s Moons

Galileo discovered Jupiter’s four largest moons: Io, Europa, Ganymede, and Callisto.

Those four are all larger than Earth’s moon.

They are all different from each other.

Since Galileo’s time, astronomers have discovered dozens more moons orbiting Jupiter. (60+ moons!) Many are very small.

{ {Io’s surface is covered with large, active volcanoes. An eruption of sulfur lava gives it unusual color.

Callisto’s surface is icy and covered with craters.

Jupiter’s Moons cntd.

{ {Ganymede is the largest moon in the solar system. It is larger than Mercury and Pluto.

Jupiter’s Moons cntd.

Jupiter’s Moons cntd.

Europa “…made out of ice and there are

hypothetical liquid oceans underneath the surface. It is the smallest of the Galilean moons and its name comes from the daughter of an ancient Phoenician king.

The surface is made out of ice and is covered in dark streaks that cover the whole surface. The origin of these streaks is unknown.

This moon is probably the likeliest candidate for extrasolar life that might live underneath the ice. It would be difficult for a space probe to drill through the ice and then survive while submerged in the ocean although it is possible in the future.”

–starsurfin.com

Saturn is the second-largest planet in the solar system.

The Voyager probes showed that Saturn, like Jupiter, has a thick atmosphere of H and He.

Saturn’s atmosphere also has clouds and storms, but less dramatic than those of Jupiter.

Saturn is the only planet whose average density is less than that of water.

Saturn

Galileo saw something sticking out on the sides of Saturn, but he didn’t know what it was.

A few decades later, when better telescopes were invented, we saw that Saturn has rings.

The rings are made of chunks of ice and rock, each traveling in its own orbit around Saturn.

Saturn has the most spectacular rings of any planet.

Saturn’s Rings

Saturn’s Rings

Saturn's rings are composed of many different rings. Some of these rings have empty spaces known as divisions. The rings are primarily made out of ice and they are so bright that they light up the nightside of Saturn.

The rings were probably formed from debris and rubble from moons or comets that got too close to Saturn and were ripped apart by its gravity.

{The space probe Cassini flew behind Saturn’s shadow and saw this image of the eclipsed sun. We learned that the dark side of Saturn is partly lit by it’s own ring system.

Saturn’s Rings cntd.

Saturn’s largest moon is called Titan. Titan is larger than Mercury.

Titan has an atmosphere so thick that little light can pass through it.

Four other moons of Saturn are each over 1,000km in diameter.

Saturn has 31+ moons total.

Saturn’s Moons

Saturn’s Moons: Titan

A recently launched probe has revealed liquid lakes on Titan; we do not know what the liquid is. Earth is the only other known planetary body to have liquid lakes ar the surface.

Because atmospheric pressure is high, and gravity is low on Titan, a person could fly through the air if they jumped!

Uranus is four times the diameter of Earth. (Much smaller than Jupiter & Saturn.)

Uranus is twice as far from the sun as Saturn, so its much colder.

It looks blue-green because traces of methane in the atmosphere. (Methane absorbs red light from the sun, so the planet appears to be turquoise.)

Surrounded by thin, flat rings. It was discovered in 1781 by William Herschel

in England. (First new planet discovered since ancient times.)

Uranus

About 200 years after Herschel died, the Voyager 2 arrived at Uranus and sent back close-up views of the planet.

Images showed few clouds on the surface.

We learned that Uranus’s axis of rotation is tilted at an angle of about 90 from the vertical. (It rotates top to bottom instead of side to side.)

Astronomers think that billions of years ago Uranus was hit by an object that knocked it on its side.

Exploring Uranus

What would seasons be like on Uranus?

Uranus has 25+ moons. The five larges have icy, cratered

surfaces. (Craters show that rocks have hit the moons.)

They also have lava flow on their surfaces, suggesting that material has erupted from inside each moon.

Uranus’s Moons

Neptune is similar to Uranus in size and color.

Neptune is a cold, blue planet. It’s atmosphere contains visible clouds.

Scientists think that Neptune is slowly shrinking, causing its interior temperature to heat up. As the energy rises towards the surface, it produces clouds and storms in the planet’s atmosphere.

Neptune

{ {Discovery of Neptune Neptune was discovered as

the result of a mathematical prediction.

(Uranus was not following it’s predicted orbit; they figured it must be because another planet’s gravitational force was acting on it.)

In 1846, mathematicians predicted the location or the unseen planet. Shortly after, it was observed.

Exploring Neptune The Voyager 2 flew by

Neptune and photographed a Great Dark Spot about the size of Earth. Probably a giant storm, but it didn’t last long.

Five years later, the spot was gone.

Other smaller spots and regions of clouds seem to come and go.

Neptune cntd.

Pluto is very different from the gas giants. Pluto has a solid surface and is much smaller and

denser than the other outer planets. Pluto is smaller than Earth’s moon. Pluto has a single moon of it’s own, Charon. Since

Charon is more than half the size of Pluto some astronomers consider them to be a double dwarf-planet instead of a planet and a moon.

Pluto was once classified as a planet, but is now called a dwarf-planet.

Pluto’s orbit is very elliptical, bringing it closer to the sun than to Neptune at one point. It’s orbit takes 248 Earth years because Pluto is 3.5 billion miles from the sun.

Pluto

This was necessary because a number of planet-like bodies at the edges of our solar system were discovered. Without a new definition of “planet” the solar system might end up with thousands of planets!

In 2006, a new definition of planet was written.

Pluto: A new definition of planet

{ {Planet A body that orbits the

sun. (Or another star.) It must be round. It must have cleared all

objects, such as other planets and asteroids, out of its path.

8 in our solar system.

Dwarf Planet A body that orbits the

sun. (Or another star.) It must be round. Its gravity isn’t strong

enough to push other objects out of its path.

4 in our solar system. (Pluto, Charon, Ceres, Eris)

Planets vs. Dwarf Planets

{ {Asteroid Belt Ceres Ceres was discovered back in

1801. It was the first object to be

discovered in the asteroid belt. (Region between inner and outer planets.)

There are million of asteroids in the belt. Most are less than a mile wide and appear in many odd shapes.

Ceres is different because it is big and has a round shape.

In 2006, scientists decided to call it a dwarf planet.

Dwarf Planets: Ceres

{ {A New Dwarf Planet Eris

Eris is the largest dwarf planet. It is also the most recently discovered.

It was found in 2005. It is almost 10 billion

miles from the sun at the farthest point in its orbit. It takes Eris 557 Earth years to complete its orbit.

Dwarf Planets: Eris

How are the gas giants similar to each other?

Why do the gas giants have thick atmospheres?

Describe an important characteristic of each of the outer planets that helps distinguish it from other planets.

How is Pluto different from the gas giants? What is the difference between a planet

and dwarf planet?

Review Questions