The Solar System

The Sun’s Family - the Giants

The Sun’s Family - the Dwarfs Earth Venus Mars GanymedeTitanMercury Callisto Io Moon EuropaTriton Pluto

Planet Types  Terrestrial  Mercury  Venus  Earth  Mars  Jovian  Jupiter  Saturn  Uranus  Neptune

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”  Diameter  Number of moons

Orbital Inclinations

Comparing the Planet Types  Distance from Sun  Diameter  Mass  Density  Composition  Rotation Rate TerrestrialJovian CloseFar SmallLarge Small Large Small Rocky Solar SlowRapid

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 Occultations Light Curve

Rings of Uranus

The Discovery of Uranus  William Hershel 1781  Perturbations in the orbit discovered  Must be due to another planet  F g  M/d 2  Mass from trends in the outer solar system iAssumed about the mass of Uranus  Distance from Bode’s Law

Bode-Titius Law Mercury d Venus e Earth  Mars f Jupiter g Saturn h Uranus i Asteroids

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 quickly  Mass 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 planet Mass 6.6 M  Magnitude 10  Clyde Tombaugh succeeds in 1930 Named Pluto Fainter than expected

Pluto Found

The Mass of Pluto  Pre-discovery 6.6 M 

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 times  Returned signal spread out in time

Planetary Observations Rotational Period  Radar

Rotational Rate by Radar  Send out signal of only one wavelength  Signal is Doppler shifted by surface of a rotating planet  Signal received spread out in wavelength Blue Shift here Red Shift here

Rotation of Mercury

Rotation of Venus  Orbital Period=224.7 d  Rotational period=243 d 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  Jupiter  No solid surface  Saturn  Nature of Rings

Rotational Period  Radar  Surface features Planetary Observations

Rotational Period  Radar  Surface features  Slant of spectral lines

Spectrum of Saturn 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  Mercury0.11  Venus0.65  Earth0.37  Mars0.15  Jupiter0.52  Saturn0.47  Uranus0.50  Neptune0.5  Pluto0.6

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