General AstronomyThe Solar System
The Inner Worlds
The Solar SystemGenerally speaking, the Solar System may be
considered to be everything bound by the gravitational influence of the Sun.
This, of course, includes• Planets• Moons• Comets• Meteoroids• Asteroids• Dust and gas• And anything else confined to orbit the Sun
The Solar SystemWe begin by examining the largest
bodies in the solar system (excluding the Sun itself) --- The Planets
All orbit the Sun in accordance with Kepler’s Laws
From antiquity to the 1700's, the known planets were
MercuryVenusEarthMarsJupiterSaturn
The Planets
• In 1781, the list became…
The Planets
MercuryVenusEarthMarsJupiterSaturnUranus
• In 1801, the list was extended to
The Planets
MercuryVenusEarthMarsCeresJupiterSaturnUranus
• By 1841, the list of planets is …
MercuryVenusEarthMarsJupiterSaturnUranusNeptune
The Planets
The PlanetsFor the last 70 years, since 1930, the order of increasing distance from the Sun has been…
Mercury
VenusEarthMarsJupiterSaturnUranusNeptunePluto
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Inner Planets
Outer Planets
Defining a PlanetOn August 24, 2006, the IAU resolved that planets and other Solar
System bodies would be defined in the following way:
• A planet is a celestial body that– is in orbit around the Sun, – has sufficient mass for its self-gravity to overcome rigid body forces so
that it assumes a hydrostatic equilibrium (nearly round) shape, and– has cleared the neighborhood around its orbit.
• A dwarf planet is a celestial body that– is in orbit around the Sun, – has sufficient mass for its self-gravity to overcome rigid body forces so
that it assumes a hydrostatic equilibrium (nearly round) shape, – has not cleared the neighborhood around its orbit, and– is not a satellite.
• All other objects except satellites orbiting the Sun shall be referred to collectively as Small Solar-System Bodies.
The Planets
Mercury
VenusEarthMars
Ceres
JupiterSaturnUranusNeptune
Eris
Pluto
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The Dwarf Planets
Haumea
Makemake
The Solar System
Viewing from above the Earth's north pole, the inner planets' orbits are too small to make out
The Inner Planets
The Inner Planets
We begin by looking at the Inner Planets and attempt to categorize their main features:
MercuryVenusEarthMars
Things to look for…• Size• Composition• Atmosphere• Temperature• Moons• Magnetic Fields• Liquid Water• Density
– A combination of size and composition
Density
The average density of an object is its mass divided by its volume
Water 1.0 gram/cubic centimeterPine wood 0.5 g/ccIron 7.9 g/cc
Substance/Object
Albedo
Enceladus 0.8
Europa 0.6
forest0.05-0.10
granite0.30-0.35
grass0.05-0.30
Mars 0.25
Moon 0.12
sand0.20-0.40
snow 0.6
soil0.05-0.30
urban areas0.05-0.20
60% of incident light is reflected
Albedo
Albedo0.0
Albedo1.0
Eccentricity
Most planetary orbits have eccentricities near 0 (a perfect circle)
MercuryMercury is a rocky, nearly airless world.
Closest to the Sun, it is both heat-seared and frozen.
There are no moons and Mercury is heavily cratered.
Physically it is smaller than Jupiter's moon, Ganymede, but it is the second densest planet in the Solar system thanks to its large, solid iron core
There is a very small magnetic field, about 1% of the Earth's. This implies that Mercury's iron core is at least partially liquid.
Mercury StatisticsMass (Kg) 3.303E+23
Radius (Km) 2439.7
Density (g/cc) 5.43
Orbital Radius (AU) 0.3871
Rotational Period (days) 58.6462
Orbital Period (days) 87.969
Eccentricity 0.2056
Tilt of Axis (degrees) 0
Orbital Inclination (degrees)
7.004
Albedo 0.10
Minimum Surface Temperature
-173 ºC (-279 ºF)
Maximum Surface Temperature
+427 ºC (801 ºF)
Atmospheric Composition Helium 42%Sodium 42%Oxygen 15%Other 1%
Mercury's DayFor many years it was thought that Mercury was 'tidal locked' to the Sun. That means it always keeps one face to the Sun, rotating in synchronization with its orbit.
We now know that this is wrong.
Mercury does rotate on its axis in about 59 earth days (while its orbital period is about 88 days; this is a 3 to 2 ratio, 3 mercury "days" every 2 mercury "years"
Mercury's Rotation and Year
Click the Sun to start a cycle
MercuryMercury has the most eccentric orbit of all the planets.
There is an odd phenomenon however…
Mercury's orbit precesses.
The point of perhelion changes very slightly each year.
Note that this cannot be explained using Newton's Laws.
Mercury's Interior
Crust
Mantle
Iron Core
Surface Features
Fault Line
Caloris Basin
(Looks a lotlike the Moon)
Transit
Venus• No magnetic field, perhaps because of
its slow rotation. • No satellites• Venus' rotation is somewhat unusual in
that it is both very slow (243 Earth days per Venus day, slightly longer than Venus' year) and retrograde
• The pressure of Venus' atmosphere at the surface is 90 atmospheres. It is composed mostly of carbon dioxide. There are several layers of clouds many kilometers thick composed of sulfuric acid.
• Venus' surface temperature is over 740 K (hot enough to melt lead).
• Physically it is close to earth only slightly smaller in size and less massive
Venus' StatisticsMass (Kg) 4.869E+24
Radius (Km) 6051.8
Density (g/cc) 5.25
Orbital Radius (AU) 0.7233
Rotational Period (days) -243.0187
Orbital Period (days) 224.701
Eccentricity 0.0068
Tilt of Axis 2.64
Orbital Inclination 3.394
Albedo 0.65
Mean Surface Temperature 482 ºC (900 ºF)
Atmospheric Pressure (bars)
92
Atmospheric Composition Carbon Dioxide 92%Nitrogen 3+ %Other trace
Venus' Interior
Atmosphere
Crust
Mantle
Core
Topography
While we can't see through Venus' cloud cover with visible light, radar is able to show us what the surface 'looks' like…
Venus
Venus’ Surface
Earth• A moderate atmosphere• A magnetic field• Geologically active• A single moon, but it is the
largest in the solar system relative to its parent body.
• Prograde rotation• 23.5 degree inclination to
the ecliptic• Presence of liquid water• Prograde orbit• Rocky
Earth's StatisticsMass (Kg) 5.976E+24
Radius (Km) 6378.14
Density (g/cc) 5.515
Orbital Radius (AU) 1.0
Rotational Period (days) 0.99727 (23.9345 hrs)
Orbital Period (days) 365.256
Eccentricity 0.0167
Tilt of Axis 23.45
Orbital Inclination 0.00
Albedo 0.37
Mean Surface Temperature
15 ºC (59 ºF)
Atmospheric Pressure (bars)
1.013
Atmospheric Composition
Nitrogen 77%Oxygen 21%Other 2%
Earth - Radar View
The Night Sky of Earth
North America by Night
Mars• Rocky• Very thin atmosphere• Magnetic field• 2 small moons, Phobos and
Deimos• Prograde rotation and orbit• Possible presence of water
frozen in deep gullys• Geologically inactive at present,
but has extinct volcanoes including Mons Olympus – largest, so far, in the explored solar system.
Mars' StatisticsMass (Kg) 6.421E+23
Radius (Km) 3397.2
Density (g/cc) 3.94
Orbital Radius (AU) 1.5237
Rotational Period (days) 1.025957
Orbital Period (days) 686.98
Eccentricity 0.0934
Tilt of Axis 25.19
Orbital Inclination 1.850
Albedo 0.15
Minimum Surface Temperature
-140 ºC (-220 ºF)
Maximum Surface Temperature
20 ºC (68 ºF)
Atmospheric Pressure (bars)
0.007
Atmospheric Composition Carbon Dioxide 95.3 %Nitrogen 2.7 %Other 1+ %
The Martian Family
Weather on Mars
Mar's Interior
Crust
Mantle
Core
The ExplorersCuriosity self-portrait
Opportunity simulated
Spirit
Pathfinder
Mars’ SurfaceMartian rovers Opportunity and Spirit are uncovering more and more evidence of an ancient wet planet
Spirit’s path as seen from Mars Global Explorer
Mars’ Surface
Approaching Columbia Hills
Mars’ Surface
EnduranceCrater
Mars – From 'Spirit'
Mars – From 'Spirit'
The next image was sent from the 'Spirit' rover from the Martian surface just before breaking down.
Size Comparisons