A Planetary Overview Courtesy: NASA. 2© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call The Sun the is largest and brightest

A Planetary Overview

Courtesy: NASA

2© Sierra College Astronomy Department


Solar System Roll Call

• The Sun the is largest and brightest object in the solar system

• The Sun is hot (5800 K on surface)• The Sun is gaseous and converts

matter into energy in core• The Sun has the greatest influence on

the rest of the solar system (light, solar wind…)




• Mercury is the smallest planet in the solar system

• It rotates every 58.6 days and revolves every 88 days and is tidally locked to the Sun

• The produces 88 days of day and 88 days of night, making temperatures extreme (425°C to -150°C).

• Two spacecraft has visited Mercury including one which orbited around Mercury




• Venus is often called Earth’s “twin” because it is nearly the same size as the Earth. But it’s nothing like the Earth…

• It rotates backwards (or upside down) very slowly

• It is covered with an atmosphere of mostly CO2 which allows a runaway greenhouse effect to occur raising the temperature to 470°C (880°F) planetwide

• Its surface pressure in 90 times greater than the Earth and there are clouds of sulfuric acid near the surface of the planet




• Earth is only world that we know of that has or had life on it

• It is the only world with a significant amount of oxygen in the atmosphere

• It is the only world with significant amounts of liquid water

• It is the closest planet to the Sun to have a moon and our Moon is quite large compared to the Earth




• Mars may bear the closest resemblance to the Earth

• It has a thin atmosphere of mostly CO2

• It has polar caps made of CO2 and water-ice

• In the past, water very likely flowed on the surface

• It has great geological wonders such as a great canyon and the largest volcano in the solar system

• It has two tiny moons

• It is the most studied extraterrestrial planet and has several spacecraft present and proposed to land or orbit Mars.




• Jupiter is largest planet in the solar system and is made mostly of gas with a Earth sized rocky-ice core in the center

• It has more than 300 times the mass and 1000 times the volume of the Earth

• Its atmosphere has many storms many of which have lasted for hundreds of years

• Its four largest moons (of 67) have interesting properties too (active volcanoes, subsurface water, magnetic fields)




• Saturn is another gaseous giant planet with a spectacular ring system

• The ring system is made of millions of ice-dust chunks orbiting around the planet

• Saturn has over 60 moons, a few of them midsize moons and one large one, Titan, which has a significant atmosphere.




• Uranus (YUR-uh-nus) is a smaller gas giant with a green-blue color due to methane

• It has several dozen moons a few of which are midsize• The entire system (planet, rings, moons) is tilted on their

side• It has been visited by only one spacecraft (Voyager 2)• Neptune is just a bit smaller than Uranus and bluer in

color• It has a dozen moons, one of which is large (Triton). Triton

is the largest moon to go backward around the planet• It has been visited by only one spacecraft (Voyager 2)



Solar System Roll Call• Pluto (and the other Dwarf Planets) are round object

which orbit around the Sun• Pluto was discovered as a planet in 1930, but was an

oddball world. One of its 3 moons is half its size (Charon). It was visited by spacecraft in 2015.

• Soon in the 1990s other objects out where Pluto lived were being discovered. One of these, Eris, was found to be a little larger than Pluto

• In 2006, the phrase “dwarf planet” was defined for these objects and asteroids (like Ceres) which were round but were found “nearby” other solar system objects. Haumea and Makemake were added in 2008.



Solar System Features

• Looking at the general characteristics, there are 4 features which stand out:

1. Patterns of motion among large bodies

2. Two major types of planets

3. Asteroids and comets

4. Exceptions to the rules



Distances In The Solar System

Measuring Distances in the Solar System

• Copernicus used geometry to determine relative distances to the planets.

• Today we measure planetary distances using radar.

• Average distances to the planets from the Sun range from .387 AU for Mercury to 39.53 AU for Pluto.



Feature 1: Patterns of Motion

• All planetary orbits are ellipses, but all are nearly circular.

• Each of the planets revolves around the Sun in the same direction.

• All planets - except Venus, Uranus - rotate in a counterclockwise direction.

• Most of the satellites revolving around planets also move in a counterclockwise direction, though there are some exceptions.



Feature 1: Patterns of Motion

• Inclination of a planet’s orbit is the angle between the plane of a planet’s orbit and the ecliptic plane (the plane of the Earth’s orbit).

• The elliptical paths of all the planets are very nearly in the same plane (inclination about 0°), though Mercury’s orbit is inclined at 7° and Pluto’s at 17°.



Planet Diameters

Diameters of Non-Earth Planets• Diameters are determined from distances

(from the Earth to the planet) and the planet’s angular size via the small angle formula

• Diameter of Sun (1.39 × 106 km) is over 100 times that of Earth (1.3 × 104 km).

• Jupiter’s diameter is 11 times that of Earth.• Pluto’s diameter is 1/5 that of Earth.



Planet MassesMass of the Planets• Kepler’s third law was reformulated by Newton

to include masses:

A3/P2 = K (M1 + M2)• Newton’s statement of Kepler’s third law allows

us to calculate the mass of the Sun.• Consider the orbits of planets around the Sun.

Since one of the masses to the Sun (the other being a planet), the sum of the two is essentially equal to the mass of the Sun, and the equation can be rewritten as:

A3/P2 = KM



Planet Masses

• We can do the same sort of calculation for planets as long as they have satellites orbiting them

• The masses of 6 of the 8 known planets can be calculated based on the distances and periods of revolution of these planets’ natural satellites.

• For Mercury and Venus, which do not possess any natural satellites, accurate determinations of their respective masses had to await orbiting or flyby space probes.



Feature 2: Classifying the Planets

• The planets (except Pluto) fit into two groups: the inner terrestrial planets and the outer Jovian planets.

Size, Mass, and Density• The Jovian planets have much bigger

diameters and even larger masses than the terrestrial planets.

• Terrestrial planets are more dense, however.• Earth is the densest planet of them all.



Classifying the Planets

Satellites and Rings• The Jovian planets have more satellites than

the terrestrials.• 4 Jovian planets: 170 total satellites as of July

2013 (67 for Jupiter, 62 for Saturn, 27 for Uranus, and 14 for Neptune).

• 4 terrestrial planets: 3 total satellites.• Pluto has 5 satellites. Eris has one satellite.

Haumea has 2. Each Jovian planet has a ring or ring system. None of the terrestrial planets do.


Terrestrial JovianNear the Sun Far from the Sun

Small Large

Mostly solid Mostly liquid & gas

Low mass Great mass

Slow rotation Fast rotation

No rings Rings

High density Low density

Thin atmosphere Dense atmosphere

Few moons Many moons

A comparison of planetary characteristics



Feature 3: Asteroids and Comets

Asteroids• These rocky bodies orbit the Sun, but are

much smaller than planets. Most lie between Mars and Jupiter

Comets• Small icy (water, ammonia, methane) objects

which occasionally visit the inner solar system and become visible

• Comets originate from two regions: the Kuiper Belt and the Öort Cloud



Feature 4: Exceptions to the Rules

• There are objects in the solar system that are unusual or have characteristics which are unusual as compared to the rest of the solar system. Some examples: Venus and Uranus rotate differently (backwards and on its

side, respectively) Small moons of Jupiter and Saturn and the large moon

Triton (around Neptune) revolve in the opposite direction of the rotation of the host planet.

While other terrestrial planets have no moons (Mercury, Venus) or tiny moons (Mars) The Earth’s moon is large compared to the Earth.


The End

Documents

A Planetary Overview Courtesy: NASA. 2© Sierra College Astronomy Department A Planetary Overview Solar System Roll Call The Sun the is largest and brightest