Transcript The Planets and Solar System Objects - Coca

Mead
Observatory
Earth
•Earth Stats:
•Radius = 6378 km
Mass = 6 x 1024 kg
Density = 5.5 g/cm3
•Knowledge of the Earth's interior comes from
seismology - the study of ground vibrations.
•Seismic waves can be reflected and refracted at
boundaries, just like light waves. Using this fact, and
other evidence, geologists have modeled the Earth's
Interior.
Earth
Above: Sumatran Earthquakes, April 2012, recorded at the
CSU’s Coca-Cola Space Science Center
Earth
Earth's structure has three primary layers.
The Core
•
About twice the size of the Moon, ~ 3400 km in radius.
•
Composed mostly of iron & nickel
•
The inner portion is solid. ~ Moon-sized.
•
The outer portion is liquid (very dense).
Convection + rotation = Dynamo effect - Magnetic field
•
The inner core rotates slightly faster than the outer
core. This may contribute to changes in Earth's
magnetic field.
Earth
The Mantle
•
Layer of composed of dense rock and metal oxides.
•
The mantle behaves as a plastic - properties of a solid
but can flow under pressure.
•
It is ~ 2900 km thick.
•
Contains 65% of Earth's mass! (Density ~ 3.5 - 5.8
g/cm3)
The Crust
•
A thin layer of silicates - granite(quartz) &
basalt(feldspar)
•
Has a relatively low density, 2.5 - 3.5 g/cm3
•
Is only between ~ 10 km & 70 km thick
Earth
Isotopes - atoms of an element with the same properties but
different masses (more neutrons)
Some isotopes are unstable and decay radioactively, releasing
energy.
Earth's interior is heated by radioactive decay.
Core temp. = 7500 K, hotter than the Sun's surface!
Differentiation - process by which a homogeneous body
becomes stratified.
This process gave Earth its layered structure.
Above: Image of
Earth and Moon
together from
NASA's Mars
Reconnaissance
Orbiter
Earth
Earth
As the Earth was heated, it became molten.
Heavier (more dense) elements sank.
Lighter (less dense) elements rose.
Tides - result from differences in gravitational force depending
on distance. Tidal forces are differential forces.
Aurora Borealis - Charged particles guided by Earth's magnetic
field toward the North Pole, which hit our atmosphere causing
it to glow. Northern Lights: Aurora Australis - southern lights
Magnetosphere - region around the Earth in which the
magnetic field keeps out charged particles flowing from the
Sun.
The Moon
The Moon
•Moon Stats:
Radius 1738 km = Rm = ¼ RE
Mass 7.4x1022 kg = Mm = 1/81 ME (gM = 1/6 gE)
Density 3.34 gm/cm3 = Dm
•Albedo - ~6%
•Lunar Temperatures: 265 F in sun and -170 F in
shade!
Lunar Rilles
Hadley
Rille
The Moon’s Features
•Highlands: ancient, heavily cratered terrain
on the moon with higher average elevation.
•Maria: lowlands; large, flat, relatively crater-free
plains on the moon. (singular = Mare) Younger
terrain. (Latin = “Seas”)
•Mountain Ranges and Valleys: Formed by impacts
and debris, not by tectonics as on Earth.
•Crater: circular depression caused by an impact.
•
Some lunar craters ~ 300 km across!!!
•
Deeper than Grand Canyon!!
Lunar
Highlands
Mountain Range
Mare or “Sea”
Rayed Crater
Rayed Crater
Central Peak Crater
The Moon
•Terminator: line separating day from night.
•Features more easily observed near the terminator.
Longer shadows!!
•Lunar interior is differentiated.
1.
It has a core with little or no iron (no magnetic
field).
2.
It has a large mantle where moonquakes occur.
3.
It has a thick crust ~ 12% of its volume.
The Moon’s Origin
Giant Impact: A Mars-sized impactor hit the protoEarth off-center. Lighter debris from the impact was
scattered into orbit and coalesced to form the Moon.
•
Explains the Moon’s small iron core
•
Explains the similarities AND the differences in
isotope abundances
•
Any volatiles would have been driven off the
Moon by the heat of the collision.
•
Collision is consistent with the present angular
momentum of the Earth-Moon system.
Mysterious
Mercury
Mercury
•Mercury Stats:
Radius: 2439 km = 0.38 RE
Mass: 0.055 ME (5.5% ME)
Density: 5.43 g/cm3
Eccentricity of Orbit: 0.206
Average distance from the sun: 0.40 AU
Maximum angle from the sun: 28 degrees
• Thus, the sun always rises or sets within ~ 2 hours
of Mercury.
• Mercury always viewed in twilight or daylight or
through thick turbulent air!
MESSENGER
Spacecraft
Mercury
•The sidereal rotation period to be ~ 59 days.
•The revolution period is 88 days. (88/3 = 29.3)
•This is a 2:3 relationship.
•Albedo – the fraction of sunlight hitting a planet that
is reflected.
•The albedo of a planet can be compared with the
albedos of materials on Earth to determine of what
material the surface of the planet is made.
•Mercury and the moon both have low albedos ~ 6%.
Mercury
•Mercury has a large core: Made of iron
~ 42% of its volume
~ 70% of its mass
• Mercury undergoes the greatest surface
temperature variations in the solar system:
during the day 427 C (800 F)
at night -183 C (-300 F)
•Mercury has almost no atmosphere.
•Mercury has no moons.
Mercury
•Mercury’s Surface:
1.
Heavily cratered in general
2.
Has large, smooth plains (like Maria)
3.
Has heavily cratered terrain (like Highlands)
4.
Has lightly cratered intercrater plains in
between.
•Mercury has very long scarps – lines of cliffs formed
as Mercury’s core cooled and shrank – “wrinkles.”
(Much longer than on the moon).
•Caloris Basin: 1300 km wide impact plain (like Mare
Imbrium) bounded by 2 km high mountains.
Caloris
Basin
Image from
MESSENGER
Spacecraft
Mercury
•Mercury has a very slight atmosphere, consisting of
Hydrogen, Helium (from the sun – solar wind),
oxygen, argon, sodium and potassium (Sodium is the
major constituent of Mercury’s atmosphere) Both
sodium and potassium are found because of
“sputtering” by solar wind).
•Mercury has a magnetc field = 0.1% BE – a partially
molten core.
Beautiful
Venus
Venus
•Earth’s “sister” planet
•“Evil step sister” --Dr. C.
•Approximately equal sizes masses and densities.
•Venus Stats
Radius – 6,052 km ~ 0.95 RE
Mass – 0.82 ME
Density – 5.24 g/cm3
Orbital Period – 225 days (sidereal!!)
Rotational Period – 243 days (retrograde!) (sidereal!)
Ave. Orbital Radius: 0.7 AU
Surface Temperature: ~ 900 F (would melt lead!!!)
Venus
• Spectra reveal the composition of the atmosphere:
carbon dioxide ~96% (<0.1% on Earth); nitrogen
nearly 4% with 02 and <1.0% H20
•Atmospheric pressure ~ 90 * Patm -E (due to CO2)
•Where’s the CO2 on Earth?
It mixed with rain and minerals to form rocks such
as limestone. Some organisms aided in this
process. It is also trapped in our ocean waters.
•Venus has no oceans and no life; CO2 is free!
Venus
• What happened to Venus’s H2O “Oceans”?
•A.
Closer to the sun
•B.
Lower atmosphere; hotter
•C.
More water vapor rose to the upper atmosphere
•D.
Solar UV broke it into H & O
•E.
H is very light and easily escaped into space!!
•F. O combined with other gasses or with iron on
the surface
Venus
• Clouds of Venus contain some H2O
but much H2SO4 – Sulfuric Acid
•Surface Temperature: intensity of emitted
radiation increases with surface temperature (black
body radiation)
•
Radio waves penetrate Venusian clouds. Radio
intensity yields surface temperature 900 F!!
•“Runaway Greenhouse Effect”
•Heat energy, released as I.R. is “trapped” by a
nearly opaque atmosphere.
•Surface temperature must climb very high before
escaping I.R. = (balances) incoming visible energy.
Mars,
The
Red
Mars
• MARS STATS
Radius – 3397 km ~ 0.53 RE
Surface Temperature -- -190 F to 80 F
Mass – 0.11 ME (~ 1/10 ME)
Density – 3.94 g/cm3 (Mars has a much smaller
core and thicker crust than Earth!)
Orbital Period – 687 days
Rotational Period (sidereal) – 24 hrs. 37 min.
Ave. Orbital Radius -- ~ 1.5 AU (semimajor axis
= 1.523 AU)
Tilt of the Axis – 25 degrees (Thus, Mars has
similar seasons! Four seasons twice as long as
Earth’s)
Mars’ atmosphere ~ 1% PatmE. Mostly CO2
How does Mars compare to
the Earth?
• The diameter of Mars is about half
that of the Earth.
• Its mass is only 1/10 of Earth’s.
The Colossal
Olympus
Mons
The largest volcano
in the solar system.
375 miles across
16 miles high
The
Valles
Marineris
The Mariner Valley
2500 miles long
125 miles wide
5 miles deep
Here are some of the
photographs from
MGS.
Notice how these features resemble gullies made
by flash flooding on the Earth.
Flash flooding creates a recognizable
formation with 3 parts.
• Groundwater erodes
away the topsoil forming
an alcove.
• Water gushes downhill
from the alcove cutting a
channel, and clearing it
of debris.
• Material swept out by the
water forms an apron of
debris at the bottom of
the formation.
•These same
structures are
observed in the
formations found on
Mars.
•Currently, scientists
find water to be the
most likely cause.
The formations on Mars seem to be
geologically recent.
Mars
Mars has two Moon.
• *Phobos (27 km across)
orbits 7h 40 min.
albedos ~ 6%
• *Deimos (15 km across)
orbits ~ 30h
albedos ~ 6%
Jupiter
Jovian Planets
In the inner solar nebula, condensation of volatile
elements was not possible because of the high
temperatures.
Only dust grains of metals, silicates, oxides, etc.,
were able to survive.
But Jupiter (5.4 AU) is 5 times and Saturn (9.4 AU) is
10 times further from the Sun than is the Earth.
Temperatures were much lower in this part of the
solar nebula.
Thus, volatile elements, including hydrogen & helium
(the most abundant) became more important
constituents of these planets.
Jovian Planets
The Jovian planets probably formed in two steps:
1. Dust grains, coated with frozen gasses, accreted
quickly to form 4 large protoplanets, each several
times more massive than the Earth.
2. The strong gravitational attraction of these
protoplanets accreted and retained large amounts
of hydrogen, helium and other volatile elements.
Rotation
All of the gas giants rotate in less than 18 hours!
Jupiter, the largest planet in the solar system, rotates in less than 10 hours!
(About 9 hr 55 min).
This rapid rotation makes the Jovian planets more oblate
Jovian Planets
The Jovian planets experience differential rotation –
different latitudes rotate at different rates.
Example: Jupiter
Near the poles
9 hr 55 min
Near the equator 9 hr 50 min
This differential rotation contributes to the banded
appearance of the Jovian atmospheres.
Belts and Zones – More easily visible on Jupiter and Saturn.
Zones – bright bands; rising gas; the tops are approximately
20 km higher than the belts; ~ 10K colder than the belts.
Belts – dark bands; falling gas; lower than the zones (thus,
about 10K warmer – getting ready to rise up again!).
Jupiter
Jupiter Stats
Radius ~ 71,500 km ~ 11.2 RE
Mass ~ 318 ME
Revolution ~ 11.9 years
Jupiter has at least one dark ring.
Jupiter has at least 17 moons, including the 4 Galilean satellites – Io,
Europa, Ganymede & Callisto
Io
very few impact craters  young surface
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hundreds of volcanic calderas – many are active
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sulfur dioxide plumes erupt 300 km high!
Europa
Jupiter
•
very smooth surface; only a few hundred meters variation in altitude 
very young surface.
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Photographs of the surface resemble images of sea ice on Earth.
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There may be liquid H2O under the icy surface; 20 km – 50 km deep
Comet Shoemaker-Levy 9
•
Collided with Jupiter in 1994 - Original body was 2 – 10 km in diameter.
•
It was broken into 21 fragments by Jupiter’s gravity - Largest
fragments 1 – 3 km in diameter.
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1st time a collision between extraterrestrial bodies was “observed” by
astronomers.
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The Great Red Spot of Jupiter – A high-pressure, anti-cyclone (rotates
counter-clockwise in the Southern Hemisphere) that protrudes above
the surrounding cloud tops.The Red Spot is about 12,000 km by 25,000
km (~ 2.5 to 3 DEarth) & has lasted for more than 300 years!
Io
Comet ShoemakerLevy 9
Saturn
Saturn
•The beautiful rings are easily visible
•Notice the gap in the rings - Cassini Division
•The shadow of the rings on the planet can be seen
•As many as six moons can be seen, including Titan
Saturn
Radius ~ 60,300 km ~ 9.4 RE
Mass ~ 95 ME
Rotation ~ 10 hr 40 min
Revolution ~ 29.4 years
Saturn has thousands of tiny ringlets; combined they form the rings.
Particle size ranges from 10-2 m to 10 m (a few km sized).
Saturn’s moons include Titan, second largest moon in the solar system.
Saturn’s rings are
actually made up
of thousands of
smaller “ringlets.”
Uranus
Uranus
Radius ~ 25,600 km ~ 4.0 RE
Mass ~ 14.5 ME
Rotation ~ 17 hr 14 min
Revolution ~ 83.75 years
Semimajor Axis ~ 19.2 AU
Uranus has (at least) 9 rings. Discovered by Occultation
Neptune
Neptune
Radius ~ 24,800 km ~ 3.9 RE
Mass ~ 17.2 ME
Rotation ~ 16 hr 7 min
Revolution ~ 163.7 years
Semimajor Axis ~ 30.1 AU
Neptune has at least 3 rings. Discovered by Voyager
Neptune’s Great Dark Spot:
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Half the size of Jupiter’s Great Red Spot
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Photographed in 1989 by Voyager 2
The Sun
Hyakutake & Hale-Bopp
Spring 1996
Spring 1997
Meteor
Showers
Tunguska