Transcript A Planetary Overview

A Planetary Overview
Courtesy:
NASA
A Planetary Overview
Solar System Roll Call
• The Sun the is largest and brightest
object in the solar system
• The Sun is hot (5800 K on surface)
• The Sun is gaseous and converts
matter into energy in core
• The Sun has the greatest influence on
the rest of the solar system (light, solar
wind…)
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A Planetary Overview
Solar System Roll Call
• Mercury is the smallest planet in the solar
system
• It rotates every 58.6 days and revolves every
88 days and is tidally locked to the Sun
• The produces 88 days of day and 88 days of
night, making temperatures extreme (425°C
to -150°C).
• One spacecraft has visited Mercury and
another one is now in orbit around Mercury
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A Planetary Overview
Solar System Roll Call
• Venus is often called Earth’s “twin” because it is
nearly the same size as the Earth. But it’s nothing
like the Earth…
• It rotates backwards (or upside down) very slowly
• It is covered with an atmosphere of mostly CO2
which allows a runaway greenhouse effect to occur
raising the temperature to 470°C (880°F) planetwide
• Its surface pressure in 90 times greater than the
Earth and there are clouds of sulfuric acid near the
surface of the planet
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A Planetary Overview
Solar System Roll Call
• Earth is only world that we know of that has
or had life on it
• It is the only world with a significant amount of
oxygen in the atmosphere
• It is the only world with significant amounts of
liquid water
• It is the closest planet to the Sun to have a
moon and our Moon is quite large compared
to the Earth
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A Planetary Overview
Solar System Roll Call
• Mars may bear the closest resemblance to the
Earth
• It has a thin atmosphere of mostly CO2
• It has polar caps made of CO2 and water-ice
• In the past, water very likely flowed on the surface
• It has great geological wonders such as a great
canyon and the largest volcano in the solar system
• It has two tiny moons
• It is the most studied extraterrestrial planet and has
several spacecraft present and proposed to land or
orbit Mars.
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A Planetary Overview
Solar System Roll Call
• Jupiter is largest planet in the solar system
and is made mostly of gas with a Earth sized
rocky-ice core in the center
• It has more than 300 times the diameter and
1000 times the volume of the Earth
• Its atmosphere has many storms many of
which have lasted for hundreds of years
• Its four largest moons (of 67) have
interesting properties too (active volcanoes,
subsurface water, magnetic fields)
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A Planetary Overview
Solar System Roll Call
• Saturn is another gaseous giant planet
with a spectacular ring system
• The ring system is made of millions of
ice-dust chunks orbiting around the
planet
• Saturn has over 60 moons, a few of
them midsize moons and one large
one, Titan, which has a significant
atmosphere.
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A Planetary Overview
Solar System Roll Call
• Uranus (YUR-uh-nus) is a smaller gas giant with a greenblue color due to methane
• It has several dozen moons a few of which are midsize
• The entire system (planet, rings, moons) is tilted on their
side
• It has been visited by only one spacecraft (Voyager 2)
• Neptune is just a bit smaller than Uranus and bluer in
color
• It has a dozen moons, one of which is large (Triton). Triton
is the largest moon to go backward around the planet
• It has been visited by only one spacecraft (Voyager 2)
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A Planetary Overview
Solar System Roll Call
• Pluto (and the other Dwarf Planets) are round object
which orbit around the Sun
• Pluto was discovered as a planet in 1930, but was an
oddball world. One of its 3 moons is half its size
(Charon). It will be visited by spacecraft in 2015.
• Soon in the 1990s other objects out where Pluto lived
were being discovered. One of these, Eris, was found to
be a little larger than Pluto
• In 2006, the phrase “dwarf planet” was defined for these
objects and asteroids (like Ceres) which were round but
were found “nearby” other solar system objects.
Haumea and Makemake were added in 2008.
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A Planetary Overview
Solar System Features
•
Looking at the general characteristics,
there are 4 features which stand out:
1.
2.
3.
4.
Patterns of motion among large bodies
Two major types of planets
Asteroids and comets
Exceptions to the rules
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A Planetary Overview
Distances In The Solar System
Measuring Distances in the Solar System
• Copernicus used geometry to determine
relative distances to the planets.
• Today we measure planetary distances
using radar.
• Average distances to the planets from
the Sun range from .387 AU for Mercury
to 39.53 AU for Pluto.
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A Planetary Overview
Feature 1: Patterns
of Motion
• All planetary orbits are ellipses, but all are
nearly circular.
• Each of the planets revolves around the Sun
in the same direction.
• All planets - except Venus, Uranus - rotate in
a counterclockwise direction.
• Most of the satellites revolving around
planets also move in a counterclockwise
direction, though there are some exceptions.
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A Planetary Overview
Feature 1: Patterns
of Motion
• Inclination of a planet’s orbit is the
angle between the plane of a planet’s
orbit and the ecliptic plane (the plane of
the Earth’s orbit).
• The elliptical paths of all the planets are
very nearly in the same plane
(inclination about 0°), though Mercury’s
orbit is inclined at 7° and Pluto’s at 17°.
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A Planetary Overview
Planet Diameters
Diameters of Non-Earth Planets
• Diameters are determined from distances
(from the Earth to the planet) and the planet’s
angular size via the small angle formula
(Cosmic Calculations 2.1)
• Diameter of Sun (1.39 × 106 km) is over 100
times that of Earth (1.3 × 104 km).
• Jupiter’s diameter is 11 times that of Earth.
• Pluto’s diameter is 1/5 that of Earth.
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A Planetary Overview
Planet Masses
Mass of the Planets
• Kepler’s third law was reformulated by Newton
to include masses (Cosmic Calculations 4.1):
a3/p2 = K (M1 + M2)
• Newton’s statement of Kepler’s third law allows
us to calculate the mass of the Sun.
• Consider the orbits of planets around the Sun.
Since one of the masses to the Sun (the other
being a planet), the sum of the two is essentially
equal to the mass of the Sun, and the equation
can be rewritten as:
a3/p2 = KM
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A Planetary Overview
Planet Masses
• We can do the same sort of calculation for
planets as long as they have satellites
orbiting them
• The masses of 6 of the 8 known planets can
be calculated based on the distances and
periods of revolution of these planets’ natural
satellites.
• For Mercury and Venus, which do not
possess any natural satellites, accurate
determinations of their respective masses
had to await orbiting or flyby space probes.
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A Planetary Overview
Feature 2: Classifying
the Planets
• The planets (except Pluto) fit into two groups:
the inner terrestrial planets and the outer
Jovian planets.
Size, Mass, and Density
• The Jovian planets have much bigger
diameters and even larger masses than the
terrestrial planets.
• Terrestrial planets are more dense, however.
• Earth is the densest planet of them all.
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A Planetary Overview
Classifying the Planets
Satellites and Rings
• The Jovian planets have more satellites than
the terrestrials.
• 4 Jovian planets: 170 total satellites as of
July 2013 (67 for Jupiter, 62 for Saturn, 27 for
Uranus, and 14 for Neptune).
• 4 terrestrial planets: 3 total satellites.
• Pluto has 5 satellites. Eris has one satellite.
Haumea has 2. Each Jovian planet has a ring
or ring system. None of the terrestrial planets
do.
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A comparison of planetary characteristics
Terrestrial
Jovian
Near the Sun
Small
Mostly solid
Low mass
Slow rotation
No rings
High density
Thin atmosphere
Few moons
Far from the Sun
Large
Mostly liquid & gas
Great mass
Fast rotation
Rings
Low density
Dense atmosphere
Many moons
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A Planetary Overview
Feature 3: Asteroids
and Comets
Asteroids
• These rocky bodies orbit the Sun, but are
much smaller than planets. Most lie between
Mars and Jupiter
Comets
• Small icy (water, ammonia, methane) objects
which occasionally visit the inner solar system
and become visible
• Comets originate from two regions: the Kuiper
Belt and the Öort Cloud
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A Planetary Overview
Feature 4: Exceptions
to the Rules
• There are objects in the solar system that are
unusual or have characteristics which are unusual as
compared to the rest of the solar system. Some
examples:

Venus and Uranus rotate differently (backwards and on its
side, respectively)
 Small moons of Jupiter and Saturn and the large moon
Triton (around Neptune) revolve in the opposite direction of
the rotation of the host planet.
 While other terrestrial planets have no moons (Mercury,
Venus) or tiny moons (Mars) The Earth’s moon is large
compared to the Earth.
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The End
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