Moon? Mercury Venus - Los Angeles Mission College · • Rangers (1961-1965) were impact probes,...

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

Announcements

• Next Midterm 10/29

Last Class

• Grade Status

• Debrief LT Sun Size & do questions

• Sun

• Earth

• Moon ??

This Class

• Moon??

• Mercury

• Venus

Spring F2015

The Moon

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

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

• mass = 5.98 x 1024 kg

• surface temp = -50°C to +50°C

• a = 1.00 AU

• P = 1.00 y

• e = 0.0167

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

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

Lunar Craters

• Numerous!

• >300,000

• Named after people: scholars, scientists, explorers

• Typical crater morphology Tycho

CopernicusKepler

Aristarchus

MareTranquillitatis

MareSerenitatis

MareCrisium

MareImbrium

Oceanus

Procellarum

MareNubium

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

CopernicusKepler

Aristarchus

MareTranquillitatis

MareSerenitatis

MareCrisium

MareImbrium

Oceanus

Procellarum

MareNubium

LET’S PRACTICE

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.

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

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

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

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

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

Moon Landing Remastered

• https://www.nasa.gov/multimedia/hd/apollo11_hdpage.html

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

Must Explain

• Similar oxygen isotopic composition to Earth

• But different chemical composition -- low density

• All igneous rock

• Same age as Earth

• Maria and Highlands

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

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

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

Spring F2015

Mercury

Mercury and the Moon

Credit: NASA/Johns

Enhanced-color Image from

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

Mercury Moon • Equatorial Diameter = 4878 km

• M = 3.31 x 1023 kg

• 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

• surface temp = -170oC to +130oC

• A = 384,400 km (from Earth!)

• P = 29.5 days (around Earth!)

• e = 0.055

Comparison of Earth and Mercury

Image Credit: NASA/Johns

Hopkins University

Applied Physics Laboratory/

Carnegie

Press Clip Water on Mercury

Surface of Mercury -- Cratering

• Heavily cratered, some large basins

• Most craters formed after era of heaviest bombardment

• Possible water ice in craters

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

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

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

Mercury (surprisingly) has been found to have ______ on its surface.

A. life forms

B. petroleum deposits

C. diamonds

D. water ice

Mercury is most like which other solar system body?

A. the Earth

B. Venus

C. the Moon

D. Mars

Spring F2015

Key Characteristics of Venus

• Similar to Earth in size

• Covered in toxic clouds

• Very VERY hot!

• Runaway Greenhouse effect

• Rotates backwards!

• No moons

• Recent volcanic activityPioneer Venus

Pioneer Visible Light Image of Venus

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

• 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

Venus & Runaway Greenhouse

Let’s Practice

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.

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.

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

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

Surface of Venus

Smooth lowlands

Highland regions:

Maxwell Montes are

~50 % higher than Mt. Everest!

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

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

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

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)

Moons of Venus

• None

• Zero

• Zip

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

Spring 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

Greenhouse Gasses

• Carbon dioxide & other gasses

• transparent to visible light

• absorb IR light

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

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

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

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

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

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

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

TED Talk, Jun 2009

WRAP-UP

Topic for Next Class

• Mars

• Jupiter & moons

• Saturn & moons

Reading Assignment

• Astro: 7

• Astropedia: 8

Homework

• No new HW yet

Moon? Mercury Venus - Los Angeles Mission College · • Rangers (1961-1965) were impact probes,...

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