Download Terrestrial Planets

Introduction
The Solar System is ordered in that the
planets form two main families:
• solid rocky inner planets and
• gaseous/liquid/icy outer planets
From observations, astronomers believe
the Solar System formed some 4.5
billion years ago out of the collapse of a
huge cloud of gas and dust
Components of the Solar System
The Sun
• The Sun is a star, a ball of incandescent gas
whose output is generated by nuclear
reactions (fusion) in its core
• Composed mainly of H (71%) and He (27%),
and traces of nearly all the other elements
• It is the most massive object in the Solar
System – 700 X the mass of the rest of the
Solar System combined
Components of the Solar System
The Planets
• Planets shine primarily by reflected
sunlight
• Orbits are almost circular lying in
nearly the same plane – Pluto is the
exception with a high inclination
(17°) of its orbit
Components of the Solar System
The Planets
• All the planets travel counterclockwise
around the Sun (as seen from high
above the Earth’s north pole)
• Six planets rotate counterclockwise;
Venus rotates clockwise (retrograde
rotation), and Uranus and Pluto appear
to rotate on their sides
Components of the Solar System
Two types of planets
• Inner planets
–Mercury, Venus, Earth, Mars
–Small, rocky (mainly silicon and
oxygen) bodies with relatively thin
or no atmospheres
–Also referred to as terrestrial
planets
Components of the Solar
System
Outer (Jovian) planets
• Jupiter, Saturn, Uranus, Neptune,
and Pluto*
• Gaseous, liquid, or icy (H2O, CO2,
CH4, NH3) composition, do not have
a well-defined surface
• Thick atmospheres
• Ring systems
• Many moons
Components of the Solar System
Bode's Law
• Predicts the spacing of the planets in the
Solar System.
• The relationship was first pointed out by
Johann Titius in 1766
• Formulated as a mathematical expression
by J.E. Bode in 1778.
• Lead Bode to predict the existence of a
planet between Mars and Jupiter (we now
recognize as the asteroid belt).
Components of the Solar System
Asteroids and Comets
• Asteroids are rocky or metallic
bodies ranging in size from a few
meters to 1000 km across (about 1/10
the Earth’s diameter)
• Comets are icy bodies about 10 km
or less across that can grow very long
tails of gas and dust as they near the
Sun and are vaporized by its heat
Components of the Solar System
Locations of Comets and Asteroids
• Most asteroids are in asteroid belt
between Mars and Jupiter indicating that
these asteroids are the failed buildingblocks of a planet
Components of the Solar System
Locations of Comets and Asteroids
• Most comets orbit the Sun far beyond
Pluto in the Oort cloud, a spherical shell
extending from 40,000 to 100,000 AU
from the Sun
• Some comets may also come from a disklike swarm of icy objects that lies beyond
Neptune a region called the Kuiper Belt
West
Hale-Bopp
Hyakutake
McNaught
Origin of the Solar System
• It is second to Pluto in
eccentricity
• It takes 88 days to orbit the
Sun
• So if you are 10 years old on
Earth, you would be 42 years
old on Mercury!
• Mercury’s rate of rotation is
59 Earth days (tidal lock w/
sun)
• Combined effect: 1 solar day
= 176 Earth days
• Axial tilt = 0°
• Mercury has no atmosphere to
speak of
• It does trap some H and He
from the solar wind
• Extreme temperatures: 700°C
daytime and –100°C nighttime
• Ancient surface: many impact
craters (like our moon)
• Gravity = 38% of Earth’s
• If you weighed 100 pounds on
Earth, you would weigh 38
pounds on Mercury
• There are inter-crater plains
• This indicates there once was
volcanic activity on Mercury
• Presence of scarps suggest
the crust cooled, shrank and
split
• Most prominent geologic
feature: Caloris Basin
• It is a large bull’s-eye crater
caused by the impact of a
large asteroid
• Mariner 10 flew by Mercury
3 times in 1974 and 1975
• Now: Messenger – launched
in the summer of 2005; had
3 fly-bys; went into orbit in
2011
http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php
MESSENGER
The Surface of
Venus
• It takes almost 225 days for
Venus to orbit the Sun
• If you were 10 years old on
Earth, you would be 16 years
old on Venus
• Since its orbit lies within
Earth’s, it is called inferior
• The rate of rotation is 243
days
• It also shows retrograde
rotation
• So the Sun rises in the west
and sets in the east
• Atmospheric Pressure is 90
times that of Earth
• The clouds are made of
sulfuric acid
• The atmosphere is almost
entirely made of CO2
• Due to the high CO2 content,
there is a runaway greenhouse
effect
• Temperatures are >900°F at
all times
• We learned of the greenhouse
effect from Venus studies
• Venus has two “continents” –
Ishtar and Aphrodite Terras
• These “continents” rise above
the rest of the terrain
• It has a “younger” surface – it
has undergone some erosion,
etc.
• Surface gravity is 91% that
of the Earth’s
• If you weighed 100 pounds
on Earth, you would weigh
91 pounds on Venus
• Evidence of Volcanism exists
• There are shield volcanoes
• Volcanic flows imaged by the
Magellan spacecraft
• Lightning was detected by the
Venera spacecraft
Venera:
• 16 missions (1960’s – ’80’s)
• 8 were landers
Magellan:
• Orbiter (1990 – ‘94)
• Radar mapped sfc
• It takes Mars 1.88 Earth years
to orbit the Sun
• If you were 10 years old on
Earth, you would be about 5 ½
years old on Mars
• A day on Mars is 24.6 hours
• Its axial tilt is 24°
• Mars has seasons just like the
Earth, but last twice as long
• Ice caps on Mars come and go
with the seasons; made
mostly of dry ice
• The atmosphere on Mars is
very thin
• Atmospheric pressure is only
0.1 of Earth’s
• It is composed mainly of CO2
• No ozone = sterilization of
surface
Mars has 2 moons:
• Phobos (means fear)
• Deimos (means panic)
• Did not form when Mars
formed – captured by gravity
• Northern Hemisphere –
rolling volcanic plains
• Southern Hemisphere –
heavily cratered highlands
• Mars appears red due to iron
oxide rich soil
• Largest volcanoes in the solar
system are found on Mars
• The largest of these is
Olympus Mons
–It measures 700 km across its
base and is 25 km high
–It is an example of a shield
volcano
Valles Marineris
• A.K.A. Mariner Valley
• 4000 km long
• 120 km across at it widest
• 7 km deep
Two types of flow features:
• Runoff channels
• Outflow channels
Other evidence:
• Sub-surface outflows
• Erosional evidence
• Mariner (fly-by)
• Viking (landers)
• Mars Pathfinder (Lander and
rover)
• Mars Global Surveyor
Mars Exploration Rovers:
• Spirit
• Opportunity
• Both landed on Mars in early
2004
• Both are still working; Spirit is
stuck!
Phoenix Lander
• Landed in 2008
• 3-month mission turned into 5months
• Search for water, life