The Solar System

The Sun’s Family - the Giants

The Sun’s Family - the Dwarfs

Earth Venus

Mars

Ganymede Titan Mercury Callisto

Io Moon Europa Triton Pluto

Object Actual Size Scaled Size Actual Distance Scaled DistanceSun 1,393,000 km 9.762 cm 0 0

Mercury 4878 0.034 57,900,000 km 4.1 mVenus 12,104 0.085 108,200,000 7.6Earth 12,712 0.089 149,500,000 10.5Mars 6746 0.047 227,900,000 16

Jupiter 143,000 1.002 778,300,000 54.5Saturn 120,500 0.845 1,427,000,000 100Uranus 51,100 0.358 2,869,600,000 201Neptune 49,500 0.347 4,497,000,000 315

Pluto 2274 0.016 5,914,000,000 414

Planet Types

TerrestrialMercuryVenusEarthMars

Jovian JupiterSaturnUranusNeptune

Overall System Properties

Orbits coplanar Orbit in same direction Most rotate in same direction Moons tend to orbit parent body in

the same direction Lenticular “laws”

DiameterNumber of moons

Orbital Inclinations

Comparing the Planet Types

Distance from Sun

Diameter Mass Density Composition Rotation Rate

Terrestrial

JovianClose Far

Small Large

Small

Large

Large Small

Rocky Solar

Slow Rapid

Planetary Observations

Mass Follow the orbit of a moon. Follow the trajectory of a

spacecraft. Perturbations in the orbit of a

nearby planet.

Planetary Observations

Radius Angular Diameter and

Distance

Angular Diameter and Distance

Telescope Field of View

Angular Diameter

(seconds of arc)

Radius Angular Diameter and

Distance Stellar Occultations

Planetary Observations

Stellar OccultationsLight Curve

Rings of Uranus

The Discovery of Uranus

William Hershel 1781 Perturbations in the orbit discovered

Must be due to another planetFg M/d2

Mass from trends in the outer solar system

i Assumed about the mass of UranusDistance from Bode’s Law

Bode-Titius Law47

10162852

100196

036

12244896

192

0.40.71.01.62.85.2

10.019.6

Mercury dVenus eEarth Mars f

Jupiter gSaturn hUranus i

Asteroids

384 388 38.8

Neptune Found Position predicted by John Couch

Adams and Urbain Jean Joseph Le Verrier

Observed by Johann Gottfried Galle and Heinrich Louis d’Arrest on Sept 23, 1846

Two moons found quicklyMass 17.2 M

Distance 30 AU

The search for Planet IX Soon became apparent that Neptune

didn’t solve all the problems New search conducted by Percival Lowell

Looking for a small Jovian planetMass 6.6 M

Magnitude 10Clyde Tombaugh succeeds in 1930

Named Pluto Fainter than expected

Pluto Found

The Mass of Pluto

Pre-discovery 6.6 M

1968 0.911968 0.91

1976 0.111976 0.11

1978 0.00021978 0.0002

More Planets?

Reanalysis of Voyager 2 data suggests that all perturbations are accounted for In fact the hunt for Pluto need not

have been conducted if more accurate data had been available

The Kuiper Belt

Radius Angular Diameter and

Distance Stellar Occultations Radar

Planetary Observations

Radar

Radius by Radar Send out very short pulse

One nanosecond is typical Signal reflects off of different parts

of the planet at different timesReturned signal spread out in time

Planetary Observations

Rotational Period Radar

Rotational Rate by Radar

Send out signal of only one wavelengthSignal is Doppler shifted by surface of

a rotating planetSignal received spread out in

wavelengthBlue Shift

hereRed Shift

here

Rotation of Mercury

Rotation of Venus

Orbital Period=224.7d

Rotational period=243d retrograde always presents the same face

toward Earth when the two planets are at their closest approach.

Radar Map of Mercury

Comparing Twins

Venus

Other Radar Findings

JupiterNo solid surface

SaturnNature of Rings

Rotational Period Radar Surface features

Planetary Observations

Planetary Observations

Rotational Period Radar Surface features Slant of spectral lines

Spectrum of SaturnRings

Rings

Planet

Slit of Spectrograph

Planetary Observations

Rotational Period Radar Surface features Slant of spectral lines Light variations

Asteroid Ida

Planetary Observations

Albedo Information required

Sun-Planet distance Planet-Earth distance Brightness of Sun Brightness of Planet

Basic Information on surface, atmosphere, clouds, ice

caps

Albedos Mercury 0.11 Venus 0.65 Earth 0.37 Mars 0.15 Jupiter 0.52 Saturn 0.47 Uranus 0.50 Neptune 0.5 Pluto 0.6

End of Section