general astronomy the solar system the inner worlds

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


Rotational Period (days) -243.0187


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’ 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


Rotational Period (days) 0.99727 (23.9345 hrs)


Eccentricity 0.0167

Tilt of Axis 23.45


Albedo 0.37

Mean Surface Temperature

15 ºC (59 ºF)


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


Rotational Period (days) 1.025957


Eccentricity 0.0934

Tilt of Axis 25.19


Albedo 0.15

Minimum Surface Temperature

-140 ºC (-220 ºF)

Maximum Surface Temperature

20 ºC (68 ºF)


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

general astronomy the solar system the inner worlds

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