The Solar System - Information Technology Servicesmason.gmu.edu/~pbecker/lectures/lecture15_handouts.pdf · 2014-11-07 · 3 The Solar System The Solar System •The distance between

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Lecture 15: The Solar System

The Solar System•All planets orbit the Sun in the same general direction, which is counterclockwise as viewed from the north celestial pole

•Most planets orbit the Sun in nearly the same plane as the Earth (the ecliptic plane)

•Mercury and Pluto are the exceptions

Venus

Mercury

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto

Asteroid Belt

The Solar System•Tilt of Mercury’s orbit is 7 degrees

•Tilt of Pluto’s orbit is 17 degrees•Most of the planetary orbits are near-perfect circles centered on the Sun

•The “eccentricity” e determines how far from circular (how elliptical) the orbit is

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aSemi-major axis

The Solar System

•Mercury and Pluto have the most eccentric (elliptical) orbits

•Mercury has an eccentricity e = 0.21 and Pluto has an eccentricity e = 0.25

Rmin= a (1-e) Rmax= a (1+e)

a = 0.5 (Rmin + Rmax)

•The eccentricity is related to the minimum and maximum distances Rmin and Rmax

•We see that

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The Solar System

The Solar System•The distance between the Earth and the Sun is one astronomical unit (AU), which is about 93,000,000 miles, or 150,000,000 km

•The distance between the Sun and Pluto is 40 AU

•Light takes about 8 minutes to travel from the Sun to the Earth

The Solar System•Light takes about 320 minutes (over 5 hours) to travel from the Sun to Pluto

•The distance to Pluto is about 0.001 light-years

•The nearest star is thousands of times farther away than Pluto

Empty Space

Nearest StarSun

Solar System

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The Solar System

Each planet is unique…

Comparative Planetology•The planets have very different sizes:

VenusSaturn

Comparative Planetology•The planets have very different appearances:

Earth

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Comparative Planetology•The planets have very different internal structures:

Saturn

Comparative Planetology•The planets have very different atmospheric structures:

EarthVenus

Comparative Planetology•The planets have very different obliquities (tilt angles):

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The Solar System•We see that the planets have different

Distances from the SunMasses

Eccentricities

Orbital inclinations

Obliquities (tilt angles)

Spin Periods

The Solar System

The Solar System•They also have different

Atmospheric temperatures

Surface pressures

Surface gravities

Compositions

Formation historiesSatellites (moons)

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•First we focus on radius, mass, and average density:

Planet Mass Radius Density

Mercury 0.06 0.38 0.98

Venus 0.8 0.95 0.95

Earth 1.0 1.0 1.00

Mars 0.11 0.53 0.71

(Ceres) 0.0002 0.07 0.5Jupiter 318 11 0.24

Saturn 95 9 0.13

Uranus 15 4 0.23

Neptune 17 4 0.30

Pluto 0.002 0.18 0.37

(where we have used Earth units)

The Solar System

•Next we focus on distance, orbital period, and spin period:

Planet Distance Orbit P Spin P

Mercury 0.4 0.24 59

Venus 0.7 0.62 -243

Earth 1.0 1.0 1.0

Mars 1.5 1.9 1.03

(asteroid) 2.8 4.7Jupiter 5.2 11.9 0.41

Saturn 9.5 29.5 0.44

Uranus 19.2 84.0 -0.72

Neptune 30.1 164.8 0.67

Pluto 39.5 248.6 -6.4

(where we have used Earth units)

The Solar System

•There are two classes of planets in the Solar System:

The Terrestrial planets are small and have high densities:

MercuryEarth

Venus

Mars

The Jovian planets are large and have low densities:

Jupiter

SaturnUranus

Neptune

•Pluto doesn’t really fit into either category very well!

The Solar System

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•The properties also differ somewhat for planets in the same group

Atmospheres

DensitiesLength of Day

•Earth is the only planet with free oxygen in its atmosphere, andwith liquid water on its surface!

•The length of the day on Earth and Mars is 24 hours, but Mercuryand Venus take months to rotate just once

•Earth and Mars have moons, but Mercury and Venus do not

•Nonetheless, the Terrestrial planets seem quite similar to each other when compared with the Jovian planets

Comparative Planetology

Comparative Planetology•The general characteristics of planets within the Terrestrial and Jovian groups are quite different:

Terrestrial

Close together in

inner solar system

Small, dense, rocky

Solid surfaces

Weak magnetic fields

Only three moons

Jovian

Widely spaced in outer solar system

Large and gaseous

No solid surfaces

Strong magnetic fields

Lots of moons

•The Sun is the dominant object in the Solar System

•It contains over 1,000 times the mass of Jupiter•The Sun contains 99.9% of the material in the Solar System

The Solar System

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•The Sun is about 10 times larger (radius) than Jupiter

•Jupiter is about 10 times larger (radius) than the Earth

The Solar System

•Interplanetary debris

Leftover from the formation of the Solar System

Ranges from large asteroids and comets to microscopic dust

Rocky material resembles the outer layers of the terrestrial planets

The Solar System

The Solar System•Interplanetary debris

The total mass of the debris is less than that of the Moon

These objects are nearly unchanged since the formation of the Solar System

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The Solar System•Meteorites allow us to study material from the early Solar System here on Earth

•Meteorites come in two groups, made mainly of either carbon or silicon

http://www.washingtonpost.com/wp-dyn/articles/A13698-2003Oct11.html

The Solar System

•Comets fall into two major groups, depending on the period of their orbits (short- and long-period comets)

•Comets are made of ice and rock, similar to the moons of the outer planets – they are also composed of ancient material

Earth

Sun

Comet Comet’s orbit

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Views of Mars

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Solar System Satellites

Jupiter and its Satellites

•The moons of Jupiter form something like a “miniature Solar system” around Jupiter

•The properties of Jupiter’s moons vary with the distance from the planet

Jupiter’s Moons

•The densities of the moons decrease with increasing distance from Jupiter

•This is called differentiation and it is similar to what we find in the progression of planetary properties in the Solar System

Io Europa Ganymede Callisto

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Jupiter’s Moons

Jupiter’s Moons

Voyager

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Solar System family portrait, February 14, 1990, by Voyager 1

Cassini’s Path

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Gravitational encounter

Voyagers 1 & 2

•Voyager 1 & Voyager 2 are the most distant man-made objects from Earth

•They are currently at distances of 88 AU and 70 AU from the Sun, respectively – and still sending and receivingsignals!

Voyagers 1 & 2

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•Voyager 1 & Voyager 2 are traveling at speeds of 3.6 AU/year and 3.3 AU/year, respectively

•At this rate, they will reach the Heliopause – the edge of the solar system – in about 2017

Voyagers 1 & 2

•The Heliopause is where the pressure of the Solar Wind equals the pressure of interstellar space

Voyagers 1 & 2