THE SOLAR SYSTEM
• The solar system consists of the Sun, the planets (including our
Earth), their satellites, plus many smaller objects, including
asteroids and comets.
• The entire solar system, including the Sun and Earth, is believed to
have been created about 4.6 billion years ago.
• The size of the solar system is not well defined; however, one
could (until recently) state it as being at least as large as the orbit
of the planet Pluto, which can be as much as 40 times Earth’s
distance from the Sun.
• Recently, detections of other objects comparable to and larger than
Pluto, at even larger distances (in the zone known as the Kuiper
Belt), have greatly extended the known size of the solar system.
• One could also define the size of the solar system to include the
entire zone in which the “solar wind” (gas outflowing from the Sun)
dominates over the gas constituting the interstellar medium (as
determined most recently by the Voyager 1 spacecraft) to about 95
times the diameter of Earth’s orbit around the Sun.
• However, the size of the solar system is quite small compared to
the distance to the closest star other than our Sun, which is
about 9000 times Neptune’s distance from the Sun.
THE SUN
• The Sun is the central object of the Solar System, around which
all the planets and other objects revolve.
• The Sun is 109 times Earth’s diameter (and 10 times the
diameter of Jupiter, the largest planet), and has more than
300,000 times Earth’s mass.
• The Sun is composed of 90% hydrogen and 10% helium (by
number of atoms), with less than 1% of all heavier elements.
• The composition of the Sun is similar to those of other stars, and
of the interstellar medium.
• The Sun derives its energy by thermonuclear fusion, in which
four atoms of hydrogen are combined to make one atom of
helium.
• The Sun and solar system are about 4.6 billion years old, but
the total lifetime of the Sun (before depleting its supply of
hydrogen fuel) is about 10 billion years.
The Sun
Jupiter to Scale
Jupiter to Scale
Earth to Scale
Earth to Scale
THE INNER SOLAR SYSTEM
MERCURY
• Mercury is the planet closest to the Sun, has a highly
eccentric orbit, and rotates on its axis 3 times for each 2
orbits around the Sun.
• Mercury has no significant atmosphere, and like the
Moon, is heavily cratered by meteoroid impacts.
• Mercury is about 1/3 Earth’s diameter, has a larger iron
core (relative to its size) than Earth, and has a weak
magnetic field.
• Close-up images of Mercury were obtained in the Mariner
10 fly-by space mission in 1974-1975.
• Currently, a new space mission, Messenger, was
launched August 2, 2004, and is due to arrive at Mercury
March 18, 2011.
Mariner 10 Images of Mercury
Mariner 10 Close-Up View of Mercury (Caloris Basin)
Mercury’s Southern Hemisphere
Mercury’s South Pole
MESSENGER MISSION TO MERCURY
• The Messenger mission to Mercury, the first since the Mariner
10 mission, was launched August 2, 2004 and is due to arrive at
Mercury March 18, 2011.
• Messenger’s mission will include two flybys of Venus and three
flybys of Mercury, before it enters orbit around Mercury in 2011.
• The primary mission, in orbit around Mercury, is planned to last
for one year.
• Scientific objectives include finding answers to the following
questions:
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Why is Mercury so dense?
What is the geologic history of Mercury?
What is the structure of Mercury’s core?
What is the nature of Mercury’s magnetic field?
What are the unusual materials at Mercury’s poles?
What volatiles are important at Mercury?
VENUS
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Venus, the second planet outward from the Sun, is nearly the same size
and mass as Earth.
The atmosphere of Venus is quite different from that of Earth; it consists
mostly of carbon dioxide with a surface pressure 90 times Earth’s sealevel atmospheric pressure, and has a surface temperature of about 750
K (= 480o C or 900o F).
Nitrogen constitutes about 3% of the atmosphere of Venus, or nearly 3
times the amount in Earth’s atmosphere.
There is very little water vapor or free oxygen in the atmosphere of
Venus.
The lack of water is thought to be one reason for the predominance of
CO2 in the atmosphere of Venus.
The surface of Venus is completely obscured, in visible light, by a dense
cloud layer containing droplets of sulfuric acid (H2SO4).
Russian lander spacecraft have imaged and otherwise studied the
surface environment of Venus at two locations.
The surface of Venus has been mapped, using radar imaging, by the
Magellan spacecraft. Both volcanic and asteroid-impact features are
present.
TWO VIEWS OF VENUS
Near UV (Pioneer Venus)
Radar (Magellan)
Soviet Venera Lander Images of the Surface of Venus
• These are, to date, the only visible-light images obtained
from the surface of Venus (at two separate locations, by two
landers).
• Both landers were only able to operate for a short period of
time before being disabled by the extreme heat of the surface
environment.
Magellan Radar Images of the Surface of Venus
Pancake-like Volcanic Lava Domes
Asteroid Impact Crater
Magellan False-Color Radar Maps of the Surface of Venus
EARTH AND MOON
• Our home planet, Earth, is unique in many respects, but is also
average among the planets of our solar system in other respects.
• Earth, as the largest of the four inner planets, is about average in
size and mass in the solar system (four planets are smaller, and
four are larger).
• Earth is the only planet in the solar system with an atmosphere
containing a significant proportion of molecular oxygen.
• Earth is also the only planet having liquid water on its surface.
• As far as we know, Earth is the only planet having living
organisms.
• With the exception of Pluto, Earth has the largest satellite (our
Moon) relative to the size of its primary.
• Our Moon is actually somewhat larger than Pluto (as are some
satellites of Jupiter and Saturn), which has led some to consider
Pluto not to be a major planet.
MARS
• Mars, the fourth planet from the Sun, is about half Earth’s
diameter and 0.1 times Earth’s mass.
• The atmosphere of Mars has less than 1% of Earth’s surface
pressure, and consists mostly of carbon dioxide.
• Mars has a colder climate than Earth; the day to night
temperature range at its equator is about the same as the
summer to winter temperature range at Earth’s south pole.
• During winters in the north or south polar regions, CO2 can
freeze to form dry ice.
• In contrast to Venus, there is evidence of water on Mars, in the
form of water ice (polar caps), as hydrated surface minerals, and
probably as underground permafrost.
• Dry riverbeds on Mars indicate that in the distant past, Mars had
a much denser atmosphere and a warmer climate than it has at
present.
• Mars has been studied by several spacecraft missions, including
orbiters and landers, and is the target of several new missions.
Mars Opposition, October 2005
Observed by Hubble Space Telescope
Composition of the Lower Atmosphere of Mars
from Viking Lander Measurements
Gas
Carbon Dioxide (CO2)
Nitrogen (N2)*
Argon (Ar)*
Oxygen (O2)
Carbon Monoxide (CO)
Water Vapor (H2O)
Neon (Ne)*
Krypton (Kr)*
Xenon (Xe)*
Ozone (O3)
*Discovered by Viking lander experiments
**Variable
Proportion
95.32%
2.7%
1.6%
0.13%
0.07%
0.03%**
2.5 ppm
0.3 ppm
0.08 ppm
0.03 ppm**
Viking Orbiter Views of Mars
Dry River Beds?
Extinct Volcano- Olympus Mons
Viking Lander Views of Mars’ Surface
Mars Pathfinder Views of Mars’ Surface
Mars Global Surveyor Images of Mars
Valles Marineris Detail
Evidence for Recent Liquid Water
South Polar Cap as Viewed by Mars Global Surveyor
Mars Odyssey Infrared Image of Mars’ Southern Hemisphere
Mars Odyssey Map of Epithermal Neutron Emission
from Mars Near-Surface Regions
Blue areas are zones indicating sub-surface water ice (permafrost).
2003 Mars Exploration Rover
(with Mars Pathfinder Sojourner rover, for scale, at right)
Mars Exploration Rover in Action (Artist’s Concept)
Map of Mars Opportunity Rover Landing Site Region
View of the Martian Surface (Gusev Crater) from Mars Rover Spirit
View of Mars Surface from Rover Opportunity,
showing Rock Outcrops
View of Mars “Bounce Rock” from Opportunity
Rover, and Rock Abrasion Tool Studies
Closeup Microscope Views of Mars Rock “Robert E”
by Opportunity Rover
Layered texture and “blueberries” indicate the rock formation was deposited
in liquid water in the distant past (sedimentary rock).
Mars Rovers Explore Their Surroundings
Mars Rover Spirit Panorama of Columbia Hills
and Gusev Crater
Mars Rover Opportunity Panorama of Olympia
Mars Reconnaisance Orbiter
• The Mars Reconnaisance
Orbiter (MRO) is the most
recent, and most technically
advanced, Mars space
mission launched by the
United States.
• MRO was launched in
August, 2005 and is planned
to go into orbit around Mars
in March, 2006.
• MRO science objectives
include studies of the
distribution of water on Mars,
in the forms of ice, liquid, and
in combination with rocks and
minerals.
• MRO will observe the entire
surface of Mars, with higher
resolution than any previous
Mars-orbiting missions.