Transcript 06_terrestrial planets

Our story so far….you tell me:
0. locating heavenly/celestial objects and their
movement in the sky
1. history, early astronomers, Copernican revolution,
Newton’s laws.
2. How we extract information from the light coming
from stars and planets
3. the form and function of telescopes and what we
can learn using them
4.Mechanism of formation of the solar systems
5. using the earth and moon to learn about terrestrial
planets and their moons
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Our story so far…
1. Our ability to observe the universe is biased
to our viewpoint….but we have learned to
break free of our bias.
2. Electromagnetic radiation, “light”, is our only
tool to observe most of the universe, but we
can learn much from EM info only
3. We have physically snooped around our
own neighborhood a bit and learned alot
4. We can better understand all solar systems
by understanding how ours was formed and
what it’s like today
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Lecture Outline
Chapter 6
The Terrestrial
Planets;
“Comparative
anatomy”
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http://video.pbs.org/video/17906
21534/
Chapter 6
The Terrestrial Planets
Pheonix
lander, 2008
True color
image.
Found ice
under the
surface
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Some news from Rosetta
http://www.nytimes.com/2014/12/11/science/rosettamission-data-rules-out-comets-as-a-source-forearths-water.html?smprod=nytcoreiphone&smid=nytcore-iphone-share
The water from the comet being studied is different
from the water on earth. More evidence that earth’s
water came from inner-system asteroids rather than
outer-system comets.
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Transit of Venus, 5 June 2012, from the dock, Lumix w/ glass filters
Next time, 2117….what could we learn from this…?
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Units of Chapter 6
Orbital and Physical Properties
Rotation Rates
Atmospheres
The Surface of Mercury
The Surface of Venus
The Surface of Mars
Internal Structure and Geological History
Atmospheric Evolution on Earth, Venus, and Mars
Summary of Chapter 6
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6.1 Orbital and Physical Properties
The orbits of
Venus and
Mercury show
that these planets
never appear far
from the Sun.
Look at Stellarium to
see what the inner
planets look like from
our spot.
Look at SolarWalk to
see them move from
above.
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6.1 Orbital and Physical Properties
The terrestrial planets have similar densities and
roughly similar sizes, but their rotation periods,
surface temperatures, and atmospheric
pressures vary widely.
How fast do the planets orbit the sun?
Why does this vary with radius?
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6.2 Rotation Rates
Mercury is difficult to
image from Earth, why?
Rotation rates can be
measured by Doppler
radar.
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6.2 Rotation Rates
Mercury’s day and year are tidally locked, but with a
twist;
Mercury rotates exactly three times while going
around the Sun twice.
This is called resonance, and tidal forces
hold this pattern in place.
Why is Mercury affected this way by the
sun, and other planets are not.
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Mercury’s orbit
• How eccentric is it? Find in book
• Show on SolarWalk
• Understand table 3A in appendix A-4
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What is link of orbit to rotation
for the planets
Planet
Years in orbit of sun
Days for rotation
Mercury
0.241
59
Venus
0.612
-243
Earth
1
1
Mars
1.88
1.03
What relation is there between orbit and rotation?
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6.2 Rotation Rates
Venus
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Mars
6.2 Rotation Rates
All the planets rotate in a forward direction,
except Venus, which is retrograde.
How could that happen?
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The Rivas theory…..
6.3 Atmospheres
Mercury has no detectable atmosphere; it is too hot,
too small, and too close to the Sun. Explain each….
Venus has an extremely
dense atmosphere. The
outer clouds are similar in
temperature to Earth, and
it was once thought that
Venus was a “jungle” planet.
We now know that its surface
is hotter than Mercury’s,
hot enough to melt lead.
The atmosphere of Mars is similar to
Earth in composition, but very thin.
Why is it thinner? What effects?
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3 Jan: 6.4 The Surface of Mercury
Mercury cannot be imaged well from Earth
(why?); best pictures are from Messenger.
Cratering on
Mercury is
similar to that
on the Moon.
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6.4 The Surface of Mercury
Some distinctive
features: Scarp
(cliff), several
hundred km long
and up to 3 km
high, thought to
be formed as the
planet cooled and
shrank.
Why are we excited to
see these features?
A: tells us about the
interior of planet
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6.4 The Surface of Mercury
Caloris Basin,
very large impact
feature; ringed
by concentric
mountain ranges
Asteroid strike
Volcanism
History
Structure
Why are the images of
mercury’s surface so
clear?
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6.5 The Surface of Venus
For venus, we have to rely
on radar (radio detection
and ranging). Why?
This map of the
surface features of
Venus is on the same
scale as the Earth map
below it.
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6.5 The Surface of Venus
Venus, imaged by the
Magellan probe
Venus does not
show tectonic
plate motion, even
though it has
volcanoes. What
explanation can
you give for this?
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5 Jan: 6.5 The Surface of Venus
Top: Lava domes on
Venus
Bottom: the volcano Gula
Mons
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6.5 The Surface of Venus
Venus corona,
with lava domes
Does Venus have
erosion? What
kind?
Wind
Liquid flow
Glacial
Dust blast
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6.5 The Surface of Venus
A photograph of the surface, from the Venera
lander (it lasted only an hour….why?)
Why can this be visible?
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9 jan: Why does our local temp vary
with daylight hours like this chart
shows?
oC
Hrs of sun
per day
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Missions to Mars
Imagine the future, if this was the recent
past! See page 174 for source….
http://www.planetary.org/blogs/emily-
lakdawalla/2012/12100800-mariner-4-mars.html
This progress is only because we kept
trying:
http://en.wikipedia.org/wiki/List_of_missions_to_Mars
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6.6 The Surface of Mars
Big topic because it is
earthlike, hospitable for life,
well studied, much history,
and interestingly variable
(volanoes, erosion, craters,
liquid water, ice)
Major feature:
Tharsis bulge, size
of North America
and 10 km above
surroundings
Minimal cratering;
youngest surface
on Mars
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Why asteroids striking mars
are useful to us
http://www.redorbit.com/news/space/1112712003/met
eorite-mars-atmosphere-101212/
Meteorites that fell in morocco in winter have been
analyzed. These are rare because the fall was
observed, they were recovered quickly before
weathering and chemical contamination could occur,
and they are from a known set of martian meteorites.
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6.6 The Surface of Mars
• Northern hemisphere (left) is rolling volcanic terrain.
• Southern hemisphere (right) is heavily cratered
highlands; average altitude 5 km above northern.
• Assumption is that northern surface is younger than
southern.
• Means that northern hemisphere must have been
flooded with lava.
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The Martian canal system
• Science ultimately arrives at an
accurate description and understanding
of nature, but rarely the first time.
• What is the story?
– 1877: Italian astronomer views “canali”
– Press stories sensationalize into “canals”
– Percival Lowell made it his mission to
prove that intelligent life made the canals
– Idea finally dies in 1970s
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A base map
shows the
locations of
all of Mariner
4's images
of Mars, shot
on July 1415, 1965.
Your eyes
are not
deceiving
you: the
base map on
which the
footprints are
drawn has
canals on it.
This was,
indeed, the
map used by
NASA to
plan the
encounter.
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6.6 The Surface of Mars
This map shows the main surface features of
Mars. There is no evidence for plate tectonics.
scarp
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6.6 The Surface of Mars
Mars has largest volcano in Solar System;
Olympus Mons:
Why are martian
• 700 km diameter at base
• 25 km high
• Caldera 80
km in diameter
Three other
Martian
volcanoes are
only slightly
smaller.
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volcanoes so
high?
6.6 The Surface of Mars
Was there running water on Mars? Probably
Runoff
channels
resemble
those on
Earth.
Left: Mars
Right: Earth
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6.6 The Surface of Mars
No evidence of connected river system;
features probably due to flash floods
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6.6 The Surface of Mars
This feature may be
an ancient river
delta. Or it may be
something entirely
different.
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6.6 The Surface of Mars
Much of northern
hemisphere may have
been ocean.
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6.6 The Surface of Mars
Recently, gullies have been seen that seem to
indicate the presence of liquid water;
interpretation is still in doubt.
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6.6 Where did the water go?
Crater below was made when surface was liquified by
impact, so points to permafrost as current home for
water.
Water is also stored in
polar ice caps. We
cannot know how much
total water is stored, but
could be oceans-worth
of water.
Why do we care
whether water is or
was there?
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6.6 The Surface of Mars: robotic missions
Left: Viking (1975-76) orbiter and lander
Right: Mars rover Sojourner, approaching rock, from
Pathfinder mother ship (1996)
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6.6 The Surface of Mars
Landscape and close-up
by Opportunity rover
(2004- )
Spirit Rover (2004- )
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Curiosity: 2012 -
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Excellent summary: http://historicspacecraft.com/Probes_Mars.html
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Cameras and Instruments on Curiosity
Mast Camera (Mastcam) - A pair of cameras mounted on the mast, approximately two meters
above the planets surface. Each camera has a different fixed focal length. The cameras are
equipped with a variety of filters and are capable of taking color images.
Chemistry & Camera (ChemCam) - The ChemCam consists of two components. The Induced
Breakdown Spectrometer (LIBS) uses laser pulses and a spectrometer to remotely gather
elemental composition data on rock and soil samples within several meters of the rover. The
Remote Micro-Imager (RMI) serves as a context imager for the LIBS instrument. The ChemCam
is mounted on the mast.
Alpha Particle X-ray Spectrometer (APXS) - Mounted on the robotic arm turret, the APXS is a
spectrometer capable of determining elemental chemistry of rock and soil samples. Less capable
versions of this experiment equipped the earlier Sojourner and Mars Exploration Rovers.
Mars Hand Lens Imager (MAHLI) - A camera imager capable of close-up, high resolution, color
images of rock and soil samples. The imager is mounted on the robotic arm turret.
Mars Descent Imager (MARDI) - A downward pointing color video camera that will image the area
around the landing site as the rover descends to the surface. The data gathered will be used to
identify local terrain features and to help plan an exploration strategy.
Radiation Assessment Detector (RAD) - An instrument to detect various forms of high-energy
radiation near the Martian surface. Information gathered will be used to better understand the
radiation levels that future human Mars missions will encounter.
Dynamic Albedo of Neutrons (DAN) - Funded by Russia, the DAN experiment will measure
hydrogen concentrations beneath the surface. Detected hydrogen might indicate the presence of
water.
Chemistry & Mineralogy X-Ray Diffraction/X-Ray Fluorescence Instrument (CheMin) - Will be
used to identify and measure concentrations of minerals in Martian rock samples.
Sample Analysis at Mars (SAM) - The SAM is a suite of sophisticated instruments designed to
analyze soil and rock samples collected from the surface and delivered to the instruments. Included
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within
the SAM is a mass spectrometer, a tunable laser spectrometer and a gas chromatograph.
This oblique, southward-looking view of Gale crater shows the landing site and the mound of
layered rocks that NASA's Mars Science Laboratory will investigate. The landing site is in the
smooth area in front of the mound (marked by a yellow ellipse, which is 12.4 miles [20
kilometers] by 15.5 miles [25 kilometers]).
Gale crater is 96 miles (154 kilometers) in diameter and holds a layered mountain rising about
Copyright(5
© 2010
Pearson Education,
Inc. the crater floor.
3 miles
kilometers)
above
6.7 Internal Structure and
Geological History
Venus
Magnetic field = 0
Melted iron core
Soft mantle
Soft crust, no techtonics
Magnetic field = 0.01 Earth
Solid mantle
Iron core
Magnetic field = 0.001 Earth
Solid mantle
Thick crust
Iron sulfide core, partly
melted
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6.8 Atmospheric Evolution on Earth,
Venus, and Mars
At formation, planets had primary atmosphere –
hydrogen, helium, methane, ammonia, water
vapor – which was quickly lost because these
are light gasses.
Secondary atmosphere – water vapor, carbon
dioxide, sulfur dioxide, nitrogen – comes from
volcanic activity and are heavier or also in form
of liquid and ice
Earth now has a tertiary atmosphere, 20 percent
oxygen, due to the presence of life.
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6.8 Atmospheric Evolution on Earth,
Venus, and Mars
Earth has a small
greenhouse effect; it is
in equilibrium with a
comfortable (for us)
surface temperature.
Started with much more
CO2, but much
absorbed into liquids
and solids on the
surface; this didn’t
happen in Venus
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6.8 Atmospheric Evolution on Earth,
Venus, and Mars
Venus’s atmosphere is
much denser and
thicker; a runaway
greenhouse effect has
resulted in its present
surface temperature of
730 K.
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Why is Mars’ atmosphere
different from Earth’s?
• Plate tectonics and volcanism is low,
keeping less CO2 trapped in surface
chemistry
• Planet cooled, freezing out more gasses
and reducing the total atmosphere
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Earth’s good luck for an
atmosphere that favors life
You should be able to explain specifically
how each of these benefit our
atmosphere
1.Not too close to sun
2.Not too far from sun
3.Magnetic field is strong
4.Tectonic activity
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Summary of Chapter 6
• Mercury is tidally locked in a 3:2 ratio with the
Sun.
• Mercury has no atmosphere; Venus has a very
dense atmosphere, whereas the atmosphere of
Mars is similar to Earth in composition but very
thin.
• Mercury has no maria, but does have extensive
intercrater plains and scarps.
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Summary of Chapter 6, cont.
• Venus is never too far from the Sun, and is
the brightest object in the sky (after the Sun
and Moon).
• It has many lava domes and shield volcanoes.
• Venus is comparable to Earth in mass and
radius.
• Large amount of carbon dioxide in
atmosphere, and closeness to the Sun, led to
runaway greenhouse effect and very hot
surface.
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Summary of Chapter 6, cont.
• Northern and southern hemispheres of Mars
are very different.
• South is higher and heavily cratered.
• North is lower and relatively flat.
• Major features: Tharsis bulge, Olympus Mons,
Valles Marineris
• Strong evidence for water on Mars in the past
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Summary of Chapter 6, cont.
• Mercury has very weak, remnant magnetic field.
• Venus has none, probably because of very slow
rotation.
• Neither Venus nor Mars show signs of
substantial tectonic activity.
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New year, new calendar, old
calendar
• See the handout
• question about September1752
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Quiz questions
1. Why does Mercury have such
extremes in temperature?
2. Why is Venus hotter than Mercury?
3. Why doesn’t Venus have a magnetic
field even though it has a molten iron
core?
4. Give some reasons why Venus has a
thicker and deeper atmosphere than
earth.
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From exam for chapters 5 and 6
105 pts: 12 short answer, 13 MX, 1 diagram
• Explain how the ocean tides are formed on earth, and
how they are more extreme at the beach than out in
the open ocean.
• Explain how the greenhouse effect works. What
gasses are necessary for this to happen? How is the
greenhouse effect important for life on earth
• Which major planetary layer of the Earth is unique
among the terrestrial planets?
• The scarps on Mercury were probably caused by…
…
The tertiary atmosphere.
cooling and
shrinking of the planet
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What diminishes an
atmosphere?
•
•
•
•
•
•
•
Heat
Solar wind
Weak mag field
Less gas available at formation
Low gravity to collect gas
Lack of volcanism
Chemical fixing of gas into rock or liquid
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Quiz and on test
• What are similarities among all the
terrestrial planets?
– All had atmosphere at early stage
– All have iron core
– All have rocky silicates as main component
– All have crust
– All have planet quakes
– All have craters
– All rotate around the sun in same direction
– All orbit the sun in same plane
– All are smaller than the jovian planets
– All have been visited by probes from earth
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Exam 1, term 2
• Chapters 5 and 6 plus calendar
• Calendar
– Leap year, leap second,
– Which parts are artificial
– Why 7-day week
– Why 12 months in a year
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Exam questions (be specific
and complete in your answers)
1. Explain how the ocean tides are
formed on earth, and how they are
more extreme at the beach than out in
the open ocean.
2. Explain how the greenhouse effect
works. What gasses are necessary for
this to happen? How is the
greenhouse effect important for life on
earth.
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