Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Moon? Mercury Venus
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Quote and Cartoon of the Day
“ A time will come when men will stretch out their eyes. They should see planets like our Earth.”
— Sir Christopher Wren
“ If we lived on a planet where nothing ever changed, there would be little to do. There would be nothing to figure out. There would be no impetus for science. And if we lived in an unpredictable world, where things changed in random or very complex ways, we would not be able to figure things out. But we live in an in-between universe, where things change, but according to patterns, rules, or as we call them, laws of nature. If I throw a stick up in the air, it always falls down. If the sun sets in the west, it always rises again the next morning in the east. And so it becomes possible to figure things out. We can do science, and with it we can improve our lives.”
— Carl Sagan
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Announcements
• Next Midterm 10/29
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Last Class
• Grade Status
• Debrief LT Sun Size & do questions
• Sun
• Earth
• Moon ??
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
This Class
• Moon??
• Mercury
• Venus
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
The Moon
The Moon
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Importance of the Moon
• Moderates wobble of Earth’s axis
• stabilizes climate
• Tides
• Cultural and Historical importance
• Only place aside from Earth we have visited in person
Image Credit: NASA
Galileo Image taken on way to Outer Solar
System
Apollo 16, Image Credit: NASA
CHARACTERISTICS OF THE MOON
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon Earth
• Equatorial Diameter = 3476 km
• mass = 7.35 x 1022 kg
• average density = 3.4 g/cc
• surface temp = -170°oC to
+130°C
• a = 384,400 km (from Earth!)
• P = 29.5 days (around Earth!)
• e = 0.055
• Equatorial Diameter = 12,756
km
• mass = 5.98 x 1024 kg
• average density = 5.5 g/cc
• surface temp = -50°C to +50°C
• a = 1.00 AU
• P = 1.00 y
• e = 0.0167
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Key Characteristics of the Moon
• No magnetic field
• Small core, no iron
• No atmosphere
• Too small & hot to hold onto gases
• gas molecules readily reach escape velocity!
• Very dry
• no sedimentary rock
• some ice may exist under the surface
Oblique View of the Lunar Crater Tycho
Credit: NASA/GSFC/Arizona State University
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Moon: The View from Earth
• Tidally coupled to the earth
• rotation = revolution
• always see same side
• Heavily cratered highlands
• Smoother, darker lowlands
• maria (“seas”)
• flooded by lava
• Cool
Farside from LRO
Credit: NASA/GSFC/Arizona State University
Nearside from LRO
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Craters
• Numerous!
• >300,000
• Named after people: scholars, scientists, explorers
• Typical crater morphology Tycho
CopernicusKepler
Plato
Aristarchus
MareTranquillitatis
MareSerenitatis
MareCrisium
MareImbrium
Oceanus
Procellarum
MareNubium
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Maria
• large, dark, basaltic plains
• lava flooded low-lying areas
• more prevalent on near side
• 1.2-4.2 billion y.o.
• radiometric dating
• crater counting
Tycho
CopernicusKepler
Plato
Aristarchus
MareTranquillitatis
MareSerenitatis
MareCrisium
MareImbrium
Oceanus
Procellarum
MareNubium
LET’S PRACTICE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
There is very little atmosphere on the Moon because
A. dry rocks on the moon absorb gases as soon as they are created.
B. it was blown away by meteor bombardment.
C. its low mass and high temperature allowed most gases to escape.
D. the gravitational tidal forces from the Earth stripped it away.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Moon
A. always points the same face towards the Sun.
B. does not rotate.
C. rotates at the same rate as the Earth rotates -- once per day.
D. rotates at the same rate as it revolves around Earth -- once per month.
LUNAR EXPLORATION
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
History of Lunar Exploration
• 1st visited by the USSR's Luna 1 and Luna 2 in 1959.
• These were followed by a number of U.S. and Soviet robotic spacecraft. US sent:
• Rangers (1961-1965) were impact probes,
• Lunar Orbiters (1966-1967) mapped the surface
• Surveyors (1966-1968) were soft landers.
• Apollo program -- Men on the Moon
• Lunar exploration resumed in the 1990s
• Clementine & Lunar Prospector
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Manned Lunar Exploration
• May 25, 1961 -- President John Kennedy committed the United States to landing a human being on the moon by 1970.
• Vehicle hefty enough to get to moon would be difficult to land: Two-module design with “disposable” lander • Command module
• The lunar landing module ( LM )
• The first human- piloted lunar landing was made July 20, 1969.
• July 1969 -- December 1972,: • 12 people reached the lunar surface
• collected 380 kg ( 840 lb) of rocks and soil
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Apollo Landing Sites
• First Apollo missions landed on safe, smooth terrain.
• Apollo 11: Mare Tranquilitatis; lunar lowlands
• Later missions explored more varied terrains.
• Apollo 17: Taurus-Littrow; lunar highlands
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Apollo Missions
• Hoax Believers, please check out Mr. “Bad Astronomy” Phil Platt’s extensive rebuttal:
• http://www.badastronomy.com/bad/tv/foxapollo.html
• And this filmmaker’s assessment of why faking it would have been harder than making it
• http://www.space.com/19531-moon-landings-faked-filmmaker-says-not-video.html
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon Landing Remastered
• https://www.nasa.gov/multimedia/hd/apollo11_hdpage.html
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon Rocks
• Igneous (solidified lava)
• No sedimentary rock
Vesicular (= containing holes
from gas bubbles in the lava) basalts, typical of
dark rocks found in maria
Breccias (= fragments of different types of rock
cemented together), also containing anorthosites (= bright, low-density rocks
typical of highlands)
Older rocks become pitted
with small micrometeorite
craters.
LUNAR FORMATION
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Must Explain
• Similar oxygen isotopic composition to Earth
• But different chemical composition -- low density
• No magnetic field
• All igneous rock
• Same age as Earth
• Maria and Highlands
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon formation
• Fission Hypothesis
• Earth broke in two (if it were spinning quickly enough)
• Condensation Hypothesis
• Earth & Moon formed as a double planet system
• Capture Hypothesis
• Earth gravitationally captured a pre-existing body
• Large-impact hypothesis
• Early earth and moon formed from the glancing collision of two protoplanets
• Resulting large body became the earth and ejected debris formed the moon
• Could have caused Earth’s 23° tilt
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Large Impact Hypothesis
• Impacting body about the size of Mars — Theia
• Impact heated material enough to melt it
• consistent with “sea of magma”
• Collision not head-on
• Large angular momentum of Earth-moon system
• Collision after differentiation of Earth’s interior
• Different chemical compositions of Earth and moon
• Earth absorbed iron core of impactor
• Molten remnant material coalesced into Moon
LET’S PRACTICE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which proposed explanation for the Moon’s origin was ruled out when the Apollo mission revealed similar abundances of isotopes of oxygen in lunar rock as on Earth?
A. that the Moon broke off from the Earth
B. that the Moon and Earth formed together out of the same material
C. that the Moon was a passing body that was gravitationally captured by the Earth
D. that the Moon was formed when a large object impacted the proto-Earth
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Mercury
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Mercury and the Moon
Credit: NASA/Johns
Enhanced-color Image from
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Mercury Key Characteristics
• Many similarities to Moon
• Tidal Resonance
• Revolution period = 3/2 times rotation period
• Extreme day/night temperature contrast
• 100 K - 600 K
• Weak magnetic field
• stronger than Venus & Mars
• Most eccentric planetary orbit (0.206)
• Smallest planet
Credit: NASA/Johns
Enhanced-color Image from
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Mercury Moon • Equatorial Diameter = 4878 km
• M = 3.31 x 1023 kg
• average density = 5.44 g/cc
• surface temp = -173°C to +430°C
• A = 0.4 AU (5.98 x 107 km)
• P = 88 Days
• e = 0.21
• Equatorial Diameter = 3476 km
• M = 7.35 x 1022 kg
• average density = 3.4 g/cc
• surface temp = -170oC to +130oC
• A = 384,400 km (from Earth!)
• P = 29.5 days (around Earth!)
• e = 0.055
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Comparison of Earth and Mercury
Image Credit: NASA/Johns
Hopkins University
Applied Physics Laboratory/
Carnegie
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Press Clip Water on Mercury
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Surface of Mercury -- Cratering
• Heavily cratered, some large basins
• Most craters formed after era of heaviest bombardment
• Possible water ice in craters
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Surface of Mercury -- Lobate Scarps
• Lobate scarps:
• huge curving cliffs
• shrinkage of the cooling core & “cracking” of the crust
Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Surface of Mercury -- Caloris Basin
• Largest Basin -- giant impact similar to crater which became Mare Imbrium
• On exact opposite side of planet -- lineated terrain
http://media.skyandtelescope.com/images/Mercury+false-color+l.jpg
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Mercury has a very thin, almost nonexistent atmosphere. This is likely to be because
A. it is hot enough to produce gas, but not big enough to hold onto it.
B. it is so dense the gas can’t escape to the surface.
C. it is rotating so fast that inertia causes the gasses to fly off the surface.
D. All of these
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Mercury (surprisingly) has been found to have ______ on its surface.
A. life forms
B. petroleum deposits
C. diamonds
D. water ice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Mercury is most like which other solar system body?
A. the Earth
B. Venus
C. the Moon
D. Mars
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Venus
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Key Characteristics of Venus
• Similar to Earth in size
• Covered in toxic clouds
• Very VERY hot!
• Runaway Greenhouse effect
• Rotates backwards!
• No moons
• No magnetic field
• Recent volcanic activityPioneer Venus
Pioneer Visible Light Image of Venus
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Basic Statistics
Venus • Equatorial Diameter =
12,104 km
• M = 4.87 x 1024 kg
• avrg. density = 5.24 g/cc
• surface temp = 472oC
• Rotation 243 dEarth
• A = 0.7 AU
• P = 225 dEarth
• e = 0.0068
Earth • Equatorial Diameter =
12,756 km
• M = 5.98 x 1024 kg
• avrg. density = 5.5 g/cc
• surf. T = -50oC to +50oC
• Rotation 1 dEarth
• A = 1.00 AU
• P = 365.256 dEarth
• e = 0.0167
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Venus
• 4 Thick Cloud Layers
• high speed winds due to convection
• Inhospitable Composition • 96% Carbon Dioxide
• 3.5% Nitrogen
• balance water, hydrochloric acid, hydroflouric acid…
• Air pressure crushing
• 90x that of Earth
• Hot enough to melt lead
• 470°C -- 880°F
Pioneer UV Light Image of Venus
Pioneer
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Venus & Runaway Greenhouse
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Why is Venus so hot?
A. Because it is so close to the Sun.
B. Because of the composition and thickness of its atmosphere.
C. Because the multitude of volcanoes produced so much hot lava.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Why is the atmospheric pressure at the surface of Venus so high?
A. It is hot, so it creates a lot of pressure.
B. Gravitational force acting on the thick, dense atmosphere.
C. The solar wind presses the atmosphere against the planet.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Unusual Rotation of Venus
• Venusian “year” 225 d
• Venusian “day” 243d
• Rotation is BACKWARDS (“retrograde”)
• “left-handed” where revolution is “right-handed”
• Off-center collision?
• Solar tides in dense atmosphere? http://www.meteormaverick.com/Venus.html
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Surface of Venus
• Can’t see through clouds -- radar
• Volcanos
• Lava plains
• Craters
• actual color is dark grey
Magellan Radar Map of Venus Looking down on North Pole
Credit: SSV, MIPL, Magell
an Team, NASA,
Planet
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Surface of Venus
Smooth lowlands
Highland regions:
Maxwell Montes are
~50 % higher than Mt. Everest!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Craters on Venus
• ~ 1000 large impact craters
• Surface not very old
• no water, no erosion
Magellan Image of Dickinsen Impact Crater
Credit: JPL/Magellan/NASA
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Magellan Radar Map
~ 400 km (250 miles)
JPL/NASA
Image Credit: JPLCredit: NASA Planetary Photojournal
Synthesized 3D view from Magellan Data
Terrestrial Example of Shield Volcano
Vulcanism on Venus
• Shield Volcanos
• directly over hot spot
• fluid magma chamber just below surface
• repeated eruptions
• Hawaiian islands are an example
• May be active
• Maat Mons
• Sapas Mons
• 2 calderas
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Baltis Vallis: 6800 km long lava flow channel (longest in the solar system!)
Aine Corona
Other Surface Features of Venus
• Associated with Vulcanism
• Lava Flows
• Some collapsed forming channels
• Coronae
• Circular bulges
• Pancake Domes
• Associated with formation of Coronae
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Venus Below the Surface
• Inferred
• Mantle
• Dense Molten Basalt
• Core
• Nickel Iron
• May be Partially Molten -- or not
• BUT no intrinsic Magnetic field
The probable structure of Venus.
(portion of image from NASA Multimedia Gallery)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moons of Venus
• None
• Zero
• Zip
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Evolution of Venus
• Complicated, poorly understood
• Venus is similar to Earth in mass, size, composition, density and distance from Sun
• No intrinsic magnetic field
• No protection from Solar Wind
• Carbon dioxide atmosphere
• runaway greenhouse effect
• Any surface water evaporated
• Surface evolution mostly volcanic
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Greenhouse Effect
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Greenhouse Effect
• Glass:
• transparent to visible light
• opaque to IR light
• Greenhouse
• visible light enters through glass
• warms ground & air
• ground & air give off IR
• IR can’t exit through glass
• Greenhouse gets warmer than outside
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Greenhouse Gasses
• Carbon dioxide & other gasses
• transparent to visible light
• absorb IR light
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Greenhouse Effect
• Sunlight energy comes in mostly as visible light
• Warms atmosphere & ground which emit IR
• IR light is absorbed by greenhouse gasses in the atmosphere
• “recycles” some of the energy — warms earth
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Greenhouse Effect
• More greenhouse gasses, more recycled energy
• Some natural/necessary to keep Earth comfortably warm
• Venus has a thick carbon dioxide atmosphere — VERY HOT
WARMUP QUESTION
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which of the following is part of the Earth’s natural greenhouse effect?
A. Earth’s atmosphere continually becomes thicker with greenhouse gases.
B. Infrared light becomes permanently trapped in our atmosphere by greenhouse gases.
C. The ozone hole causes significant increases in surface temperature.
D. Earth’s surface and atmospheric gases absorb energy and then give off infrared light.
E. Heat is transferred in the atmosphere through the circulation of greenhouse gases.
LECTURE-TUTORIAL GREENHOUSE EFFECT
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which of the following is part of the Earth’s natural greenhouse effect?
A. Earth’s atmosphere continually becomes thicker with greenhouse gases.
B. Infrared light becomes permanently trapped in our atmosphere by greenhouse gases.
C. The ozone hole causes significant increases in surface temperature.
D. Earth’s surface and atmospheric gases absorb energy and then give off infrared light.
E. Heat is transferred in the atmosphere through the circulation of greenhouse gases.
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
If Earth’s atmosphere were able to completely absorb visible light, which of the following would be true?
A. The Earth’s surface temperature would be cooler than it is today.
B. The Earth’s surface temperature would be warmer than it is today.
C. The Earth’s surface temperature would be the same temperature as it is today.
D. There is not enough information to answer this question.
HUMANS AND CLIMATE CHANGE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Greenhouse Effect
• Is a natural process
• Essential to maintain Earth’s temperature
• HOWEVER
• Human activity has dramatically increased the level of greenhouse gasses
• Esp. via the internal combustion engine
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Global Warming
• Beyond any reasonable doubt, the average temperature on Earth is increasing.
• loss of glaciers & polar ice caps
• rising sea water levels
• global climate change
NASA Goddard Institute for Space Studies
ICE MELT
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
TED Talk, Jun 2009
WRAP-UP
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Topic for Next Class
• Mars
• Jupiter & moons
• Saturn & moons
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Reading Assignment
• Astro: 7
• Astropedia: 8
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Homework
• No new HW yet