Properties of the Planets

• Terrestrial Planets

– Mercury

– Venus

– Earth

– Mars

• Jovian Planets

This presentation will show you some of the important physical differences between the Terrestrial and Jovian Planets. First the

Terrestrial planets…

MercuryMercury: Heavily cratered ancient rocky surface. The innermost of the planets. We have only photographed half of its surface because the planet rotates very slowly and the flyby spacecraft (Mariner) could only photograph the sunlit portion.

VenusVenus: Covered from pole to pole with bright clouds. The surface cannot be seen from orbit at visual wavelengths. Radar instruments on the Magellan spacecraft mapped the surface and found very few craters suggesting an active geology that erases resurfaces the ancient landscapes

EarthEarth: The only planet with liquid water on its surface and the only planet with molecular oxygen in its atmosphere. The Earth’s surface, like that of Venus, has very few impact craters, due to an active geology (plate tectonics) and robust weathering from wind and rain.

Mars

Mars: The last Terrestrial planet. If has an anomolusly low density for a terrestrial planet, suggesting that it is made of a different mix of materials than the other terrestrial planets. Its surface shows signs of ancient geology, but no evidence recent wide scale activity. Where is the water on Mars is the focus of current scientific work.

Properties of the Planets

• Terrestrial Planets

– Mercury

– Venus

– Earth

– Mars

• Jovian Planets

– Jupiter

– Saturn

– Uranus

– Neptune

Now, the Jovian planets...

JupiterJupiter: The closest Jovian planet. Composed almost entirely of hydrogen and helium gas, this planet began as a giant ball of ice and rock that attracted a deep atmosphere of gas from the nebula (cloud of gasses) the Sun and planets formed from.

SaturnSaturn: Almost ten times farther from the Sun than the Earth, this could world of gasses the most spectacular set of rings of all the Jovian planets. The rings are believed to be the remains of a moon that drifted to close to Saturn abd broke apart, distributing its material around the equatorial plane.

Uranus

Unanus: The first telescopically discovered (1781) planet. It remains the most mysterious of planets. No clouds can be seen it is hydrogen and helium atmosphere tinted blue by a slight enrichment of methane. Further adding to the mystery, the rotation axis of Uranus is tipped almost 90 degrees relative to the ecliptic suggesting some catastrophic event slammed into Uranus and “knocked” it over.

NeptuneNeptune: Much like Uranus in appearance, size and compostion, although cluds can be seen throuogh the atmosphere. These most distant Jovian planets are the runts of the Jovian litter, yet they still occupy a volume more than that of 64 Earth’s.

Properties of the Planets

• Terrestrial Planets

– Mercury

– Venus

– Earth

– Mars

• Jovian Planets

– Jupiter

– Saturn

– Uranus

– Neptune

What about Pluto?We’ll cover Pluto a bit later…..

Pluto

Pluto: As we shall see shortly, Pluto is a world that doesn’t fit the pattern established by the other planets. It is far too small and of the wrong composition to be a Jovian planet and too small, too far away and the wrong composition to be a Terrestrial planet. Pluto, shown here with its moon Charon, may be pieces of a planet that was not able to finish its formation. It is considered to be a piece of debris leftover from the era of planet formation.

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto

Let’s look at the numbers. Please try to see the similarities within each class of planet and the contrasts between them.

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39

Venus 0.72

Earth 1.0

Mars 1.5

Jupiter 5.2

Saturn 9.5

Uranus 19

Neptune 30

Pluto 39

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39

Venus 0.72

Earth 1.0

Mars 1.5

Jupiter 5.2

Saturn 9.5

Uranus 19

Neptune 30

Pluto 39

Terrestrial Planets

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39

Venus 0.72

Earth 1.0

Mars 1.5

Jupiter 5.2

Saturn 9.5

Uranus 19

Neptune 30

Pluto 39

Terrestrial Planets

Jovian Planets

Earth1”

Jupiter5.2”

Uranus19”

Pluto39”

Neptune30”

Saturn10”

Meter-stick Ninja

This meter stick ninja is a cute way of visualizing the relative distances of the planets form the Sun. In this image, imagine that 1 inch equals 1 A.U. Since there are about 39 inches in a meter, the entire retinue of planets can be placed on a single meter stick at this scale.

Earth1”

Jupiter5.2”

Uranus19”

Pluto39”

Neptune30”

Saturn10”

Meter-stick Ninja

Mercury 1/3”Venus ¾”Mars 1 ½”

Notice that, at this scale, all the Terrestrial Planets are within 1½ inches from the Sun. The Jovian planets are spread between 5 inches and 30 inches.

Sunrise on the PlanetsA simulation

The next series of slides are meant to help you visualize the effect of the vast distances of the Solar

System by simulating, in a simple way, what sunrise would look like from each planet, taking

into account its distance from the Sun. At the bottom of each slide appears the amount of solar

energy available at that distance from the Sun. The solar energy follows an inverse square law like gravity. Notice how rapidly the available solar energy drops as you progress through the solar

system.

Sunrise on Mercury

Available Solar Energy ~9,350 W/m2

Sunrise on Earth

Available Solar Energy ~1,350 W/m2

Sunrise on Jupiter

Available Solar Energy ~50 W/m2

Sunrise on Saturn

Available Solar Energy ~15 W/m2

Sunrise on Uranus

Available Solar Energy ~4 W/m2

Sunrise on Neptune

.

Available Solar Energy ~1.6 W/m2

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06

Venus 0.72 0.82

Earth 1.0 1.0

Mars 1.5 0.11

Jupiter 5.2 318

Saturn 9.5 95

Uranus 19 14

Neptune 30 17

Pluto 39 0.002

Now we’ll compare the masses of the planets. Note that we will use the Earth as a standard mass for convenience.

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06

Venus 0.72 0.82

Earth 1.0 1.0

Mars 1.5 0.11

Jupiter 5.2 318

Saturn 9.5 95

Uranus 19 14

Neptune 30 17

Pluto 39 0.002

Terrestrial Planets

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06

Venus 0.72 0.82

Earth 1.0 1.0

Mars 1.5 0.11

Jupiter 5.2 318

Saturn 9.5 95

Uranus 19 14

Neptune 30 17

Pluto 39 0.002

Terrestrial Planets

Jovian Planets

Imagine a “planetary balance” that could weight the planets in terms of Earth masses. How would the other planets compare?

About 9 planet Mars’ to equal

one Earth

About 17 planet Earth’s to equal

one Neptune

About 318 planet Earth’s to equal

one Jupiter

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38

Venus 0.72 0.82 0.95

Earth 1.0 1.0 1.00

Mars 1.5 0.11 0.53

Jupiter 5.2 318 11.2

Saturn 9.5 95 9.5

Uranus 19 14 4.0

Neptune 30 17 3.9

Pluto 39 0.002 0.18

Now, we’ll

examine the radii

of the planets.

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38

Venus 0.72 0.82 0.95

Earth 1.0 1.0 1.00

Mars 1.5 0.11 0.53

Jupiter 5.2 318 11.2

Saturn 9.5 95 9.5

Uranus 19 14 4.0

Neptune 30 17 3.9

Pluto 39 0.002 0.18

Terrestrial Planets

Terrestrial Planet Radii

These images of the

Terrestrial planets are

approximately to scale.

Earth

Venus

Mars

Mercury

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38

Venus 0.72 0.82 0.95

Earth 1.0 1.0 1.00

Mars 1.5 0.11 0.53

Jupiter 5.2 318 11.2

Saturn 9.5 95 9.5

Uranus 19 14 4.0

Neptune 30 17 3.9

Pluto 39 0.002 0.18

Terrestrial Planets

Jovian Planets

Jovian Planets radiiThese images of the Jovian planets are

approximately to scale.

Jupiter

Saturn Saturn

Uranus

Neptune

Jovian Planets compared to Earth

Jupiter

Saturn

Uranus

Neptune

Earth

Notice how large all the

Jovian planets are

compared to the largest Terrestrial

Planet, Earth

A Mnemonic for the Radii of Terrestrial Planets

Pluto R 51

Moon R 41

Mercury R 31

Mars R 21

Venus R 1

…and FriendsThis is a useful memory aid for the radii of Terrestrial Planets.

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38 5.4

Venus 0.72 0.82 0.95 5.2

Earth 1.0 1.0 1.00 5.5

Mars 1.5 0.11 0.53 3.9

Jupiter 5.2 318 11.2 1.3

Saturn 9.5 95 9.5 0.7

Uranus 19 14 4.0 1.3

Neptune 30 17 3.9 1.6

Pluto 39 0.002 0.18 2.0

Now, We’ll examine density. Density of an object tells a scientist something about the composition of the object. Some bench mark densities follow:

Material Density

Water 1.0 g/cm3

Rock 3 to 5 g/cm3

Iron 7.8 g/cm3

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38 5.4

Venus 0.72 0.82 0.95 5.2

Earth 1.0 1.0 1.00 5.5

Mars 1.5 0.11 0.53 3.9

Jupiter 5.2 318 11.2 1.3

Saturn 9.5 95 9.5 0.7

Uranus 19 14 4.0 1.3

Neptune 30 17 3.9 1.6

Pluto 39 0.002 0.18 2.0

Most Terrestrial Planets have densities around 5.3 g/cm3 indicating a composition of mostly rock with a smaller

amount of iron

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38 5.4

Venus 0.72 0.82 0.95 5.2

Earth 1.0 1.0 1.00 5.5

Mars 1.5 0.11 0.53 3.9

Jupiter 5.2 318 11.2 1.3

Saturn 9.5 95 9.5 0.7

Uranus 19 14 4.0 1.3

Neptune 30 17 3.9 1.6

Pluto 39 0.002 0.18 2.0

Most Terrestrial Planets have densities around 5.3 g/cm3 indicating a composition of mostly rock with a smaller

amount of iron

Mars, however, has a anomalously low density. We’ll try to explain why the density is

low when we discuss planet formation.

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38 5.4

Venus 0.72 0.82 0.95 5.2

Earth 1.0 1.0 1.00 5.5

Mars 1.5 0.11 0.53 3.9

Jupiter 5.2 318 11.2 1.3

Saturn 9.5 95 9.5 0.7

Uranus 19 14 4.0 1.3

Neptune 30 17 3.9 1.6

Pluto 39 0.002 0.18 2.0

The Jovian planet densities are MUCH lower than the

Terrestrial planets. These densities are consistent with a compositon of compressed gas.

Density Trend in the Solar System

0

1

2

3

4

5

6

0 5 10 15 20 25 30 35 40

Distance from Sun, AU

Den

sity

, gm

/cc

Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

This graph displays the density vs. distance from the Sun for each planet

Density Trend in the Solar System

0

1

2

3

4

5

6

0 5 10 15 20 25 30 35 40

Distance from Sun, AU

Den

sity

, gm

/cc

Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

This trend can be model by the dotted line.

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38 5.4

Venus 0.72 0.82 0.95 5.2

Earth 1.0 1.0 1.00 5.5

Mars 1.5 0.11 0.53 3.9

Jupiter 5.2 318 11.2 1.3

Saturn 9.5 95 9.5 0.7

Uranus 19 14 4.0 1.3

Neptune 30 17 3.9 1.6

Pluto 39 0.002 0.18 2.0

This slide contrasts Pluto’s properties with the other planets. You can see that it does not fit the pattern of the Jovian planet in mass, radius or density. Neither does it fit the Terrestrial planets.

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38 5.4

Venus 0.72 0.82 0.95 5.2

Earth 1.0 1.0 1.00 5.5

Mars 1.5 0.11 0.53 3.9

Jupiter 5.2 318 11.2 1.3

Saturn 9.5 95 9.5 0.7

Uranus 19 14 4.0 1.3

Neptune 30 17 3.9 1.6

Pluto 39 0.002 0.18 2.0In my on-site class I ask my students to memorize the numbers you can see on this slide. I expect no less of you.

PlanetDistance from

Sun, AU

Mass

MEarth

Radius

REarth

Density

gm/cm3

Mercury 0.39 0.06 0.38 5.4

Venus 0.72 0.82 0.95 5.2

Earth 1.0 1.0 1.00 5.5

Mars 1.5 0.11 0.53 3.9

Jupiter 5.2 318 11.2 1.3

Saturn 9.5 95 9.5 0.7

Uranus 19 14 4.0 1.3

Neptune 30 17 3.9 1.6

Pluto 39 0.002 0.18 2.0

Please notice that the closest Jovian planet, Jupiter, is also the largest in mass and radius. We will have an explanation for why the closest Jovian planet is the largest and why the succeeding Jovian planets tend to get smaller in mass and radius when we look at the formation of the Solar System.

Planetary Systems are characterized by two classes of planets with mutually exclusive properties.

Planetary Systems are characterized by two classes of planets with mutually exclusive properties.

• Terrestrial Planets– Close to the central star

– Small in mass and radius

– High density

Planetary Systems are characterized by two classes of planets with mutually exclusive properties.

• Terrestrial Planets– Close to the central star

– Small in mass and radius

– High density

• Jovian Planets– Far from the central

star

– Large in mass and radius

– Low density

Planetary Systems are characterized by two classes of planets with mutually exclusive properties.

• Terrestrial Planets– Close to the central star

– Small in mass and radius

– High density

• Jovian Planets– Far from the central

star

– Large in mass and radius

– Low density

Why are planetary systems organized in this manner?

Is there an over-arching principle that explains this pattern?

How common are planetary systems around other stars and how common are Earth-like planets?

Planetary Systems are characterized by two classes of planets with mutually exclusive properties.

• Terrestrial Planets– Close to the central star

– Small in mass and radius

– High density

• Jovian Planets– Far from the central

star

– Large in mass and radius

– Low density

Why are planetary systems organized in this manner?

Is there an over-arching principle that explains this pattern?

How common are planetary systems around other stars and how common are Earth-like planets?

Planetary Systems are characterized by two classes of planets with mutually exclusive properties.

• Terrestrial Planets– Close to the central star

– Small in mass and radius

– High density

• Jovian Planets– Far from the central

star

– Large in mass and radius

– Low density

Why are planetary systems organized in this manner?

Is there an over-arching principle that explains this pattern?

How common are planetary systems around other stars and how common are Earth-like planets?

Planetary Systems are characterized by two classes of planets with mutually exclusive properties.

• Terrestrial Planets– Close to the central star

– Small in mass and radius

– High density

• Jovian Planets– Far from the central

star

– Large in mass and radius

– Low density

Why are planetary systems organized in this manner?

Is there an over-arching principle that explains this pattern?

How common are planetary systems around other stars and how common are Earth-like planets?

We will answer these questions later.