TtiTerrestria allPl t Planetspeople.physics.tamu.edu/depoy/astr101/Notes/lecture9.pdf · 2009-02-06 · Low-mass atoms escape firmass atoms escape fir massive ones. v esc v escapespeed

T t iTerrestriaMonday, F

l Pl tal PlanetsFebruary 9

Family portrait of

Mercury, Venus, EarthU N tUranus, Neptune,

My Very Excellent MotMy Very Excellent Mot(Extra Che

f the Solar System:

h, Mars, Jupiter, Saturn, (E i C Pl t )(Eris, Ceres, Pluto):

ther Just Served Us Ninether Just Served Us Nineeese Pizzas).

The SolarThe SolarList of Ing

IngredientIngredient

SunJupiterJupiterother planetseverything else

r System:r System: gredients

Percent of total massPercent of total mass

99.8%0 1%0.1%0.05%0.05%

The Sun dominates the Solar System

Jupiter dominaates the planets

A th SiAnother Size C ie Comparison

Object Mass1) Sun2) Jupiter

330,000320 102) Jupiter

3) Saturn4) N

3209517

101124) Neptune

5) Uranus1715

1213

6) Earth7) Venus

1.00 82

14157) Venus

8) Mars0.820.11

1516

9) Mercury 0.055 17

Object Mass

0) Ganymede 0.0250) Ganymede1) Titan2) C lli

0.0250.0230 0182) Callisto

3) Io0.0180.015

4) Moon5) Europa

0.0120 0085) Europa

6) Triton0.0080.004

7) Pluto 0.002

The terrestrial planets rock and

Mercury, Venus, Earth, & M

The terrestrial planets are: low in mass (< Earth mass)( )high in density (> 3900 kg/

Water = 1000 kg/m3

Air = 1 kg/m3Air = 1 kg/m3

Rock = 3000 kg/m3g

are made primarily of d metal.

Mars.

) )/m3).

The mass of a planet isThe mass of a planet isNewton’s version of applied to a satellite (

h d i iThe average density is volume (for a sphere,vo u e ( o a sp e e,

The density of terrestrithan that of rock, reflextremely dense metaextremely dense meta

s determined bys determined by Kepler’s Third Law, (natural or artificial).

di id d bmass divided by , V = [4/3] r3)., V [ /3] ).

ial planets is greater lecting the presence of al coresal cores.

The study of seismicthe Earth’

How can we study the deep interior of the Earth?interior of the Earth?

Average density of the Earthg y= 5500 kg/m3

Earth is too dense to be solid rock: Basalt = 3300 kg/m3

Granite = 2700 kg/m3Granite = 2700 kg/m3

waves tells us about s interior.

h

Earthquakes produce twq p

P waves [Primary, Pressurthrough solids and liquid

S waves [Secondary ShearS waves [Secondary, Shearwaves that do NOT trave

wo types of seismic waves:yp

e]: Sound waves travel s.

r]: Transverse (side to side)r]: Transverse (side-to-side) el through liquids.

Seismic waves radiating through the Earth after anthe Earth after an earthquake:

Note: S waves doNote: S waves do not travel through the outer core!

The earth is layered inner core, an

From the outside in:

1) Crust: solid rocksolid rock 5 km thick basalt (ocean35 k thi k it (35 km thick granite (con

2) Mantle:2) Mantle: partly solid rock, partly 2900 km thick

into a crust, mantle, nd outer core.

n floor) ti t )ntinents)

semisolid (plastic) rock

3) Outer (liquid) core:3) Outer (liquid) core:molten iron and nickel 2200 k thi k2200 km thick

4) Inner (solid) core:4) Inner (solid) core:solid iron and nickel 1300 km in radius

The Earth is layeredThe Earth is layered differentiation

When young, the Earth was heatedEarth was heated by the impact of

l i l Fplanetesimals. For a while, the Earth was molten.

In a liquid, denseIn a liquid, dense stuff sinks, low-density stuff floatsdensity stuff floats.

because it underwentbecause it underwent n when molten.

When differentiation was coWhen differentiation was co(partly) solidified.

Crust of the ocean floor floaCrust of the ocean floor floaon cocoa”; lower-density “marshmallo s”“marshmallows”.

omplete, Earth cooled andomplete, Earth cooled and

ats on the mantle “like skinats on the mantle like skin continents are the

The lithosphere is brThe lithosphere is brmove relative

The crust plus the upper mantle form the lithosphermantle form the lithospher(solid but brittle).

Beneath the lithosphere is theasthenosphere (plastic)asthenosphere (plastic).

The asthenosphere, p ,heated from below, undergoes convectionundergoes convection.

roken into plates thatroken into plates that to each other.

rere

e

Conveection

Convection currents in thethe lithosphere into

There are 1

e asthenosphere have broken o sections called plates.

5 large plates.

Continuing convection inContinuing convection in plates to move relative t

The study of plate motion

The motion of continents was first suspected by p ySir Francis Bacon (17th

Best known for leadingBest known for leading scientific revolution witnew 'observation and experimentation' theory

the asthenosphere causesthe asthenosphere causes to each other.

n is called plate tectonics.

cent). thethe

th his .

America and EuropeAmerica and Europe are moving apart by 3 centimeters per year (= 30 km per million ( pyears).

This “continental drift” is measured using gGPS (global positioningpositioning systems).

Earth &

Moon diameter = 0 27 E h di0.27 x Earth diameter

Earth-Moon distance = 380,000 km = 30 x Earth diameter 30 x Earth diameter

& Moon

Apollo MissionsApollo Missions to the Moon (1969-1972)

h b kBrought back 382 kg of rocks 38 g o oc sfor chemical analysis, radioactiveradioactive dating.

CurrentCOLLISIONAL EJ

A protoplanet the size of MA protoplanet the size of Man oblique blow, just o

t favorite:JECTION THEORYMars struck the young EarthMars struck the young Earth over 4.5 billion years ago.

Computer simulationComputer simulation of impact:

Mantle of the colliding body wascolliding body was ejected to form the MMoon.

Iron core of theIron core of the colliding body sank t th E th’ tto the Earth’s center.

This dramatic collision likeThis dramatic collision likewas almost completely fol ld halmost as old as the age o

● Age of oldest Earth rocks● Age of oldest Earth rocks

● Age of oldest Moon rocks

● Age of oldest meteorites (th l t E th) 4 5the plunge to Earth) = 4.5

ly happened when Earthly happened when Earth ormed. Age of the Moon f h ld iof the oldest meteorites:

= 4 billion years 4 billion years

s = 4.5 billion years

(meteoroids that survive 56 billi56 billion years

Mercury’s uy

Orbital period = 87.969 day

Rotation period = 58.646 d

Mercury is NOT in synchroy yper orbit).

Instead, it has 3-to-2 spin-ofor 2 orbits).

unusual orbit

ys

days = (2/3) x 87.969 days

onous rotation (1 rotation (

orbit coupling (3 rotations

3-to-2 spin-orbit coupling(RIGHT!)(RIGHT!)

Synchronous yrotation

(WRONG!)(WRONG!)

Time between one noonand the next is 176 days176 days.

Sun is above the horizonfor 88 days at the time

Daytime temperatures reDaytime temperatures re700 Kelvin (800 degre

Nighttime temperatures 100 Kelvin ( 270 degr100 Kelvin (-270 degr

n

n e.

each as high as:each as high as: ees F).

drops as low as: rees F)rees F).

Mercury has no permanMercury has no permanit is too hot (and has

Temperature is a measure of themeasure of the random speed of atoms (oratoms (or molecules).

At a given temperature, massive atoms move more slowly than low-mass atoms.

HOT/COLD

nent atmosphere becausenent atmosphere because s low escape speed).

3kT3

mkTv

(Kelvin)retemperatu atom of speed typical

Tv

(molecule) atomot mass (Kelvin)retemperatu

mT

nature ofconstant a k

If an atom’s speed is greateIf an atom s speed is greatewill fly away on a hype

Low mass atoms escape firLow-mass atoms escape firmassive ones.

vesc

speedescapev

esc

planet of mass speedescape

Mv

planet of radius p

rconsta universal G

er than the escape speed, iter than the escape speed, it erbolic orbit.rst then “sluggish”rst, then sluggish ,

2GMr

n gravitatio ofant

Daytime on Earth:Daytime on Earth:T = 300 Kelvin, vesc = 11H d d h liHydrogen and helium esc

Daytime on Mercury:Daytime on Mercury:T = 700 Kelvin, vesc = 4.3AllAll gases escape.

Daytime on the Moon:Daytime on the Moon:T = 260 Kelvin (no green

2 4 k /vesc = 2.4 km/sec Because vesc is low, all ga

.2 km/sec cape.

3 km/sec

nhouse effect)

ases escape, despite low T.

Only one spacecraft y phas visited Mercury: MarinerMercury: Mariner 10 (a fly-by).

It has only imaged 45% of Mercury’s surface.

Like the Moon MeLike the Moon, Mehighlands and smooth

h h i h fThe hemisphere of Mercury that has been photographed resembles the Moon: (Crater walls are slightly lower.)slightly lower.)

ercury has crateredercury has cratered h, lava-covered plains.

Highlands areHighlands are heavily cratered.

L l i i tLow-lying impact basins, such as the Caloris basin arebasin, are covered with

h lsmoother lava flows.

Unique mercU que e cOpposite the Caloris ba

fill d i h lfilled with clo

curian feature:cu e u easin is “jumbled terrain”,

l d hillosely spaced hills.

“Jumbled terrain” was creafrom the Caloris impact co

(Planet acts as(Planet acts as

ated when seismic waves onverged on the antipodes. a giant “lens”).a giant lens ).

Mercury has an extreMercury has an extrecor

Mercury is exceptionall400 k / 35400 km/m3.

The Earth is slightly deThe Earth is slightly deit is compressed by its

Mercury must have a hu(probably mostly iron

emely large iron-richemely large iron rich re.

ly dense:

enser but only becauseenser, but only because s own strong gravity.

uge dense core n, like Earth’s).

Radius of Mercury = 2400 km.

R di f iRadius of iron core = 1800 km.

Return to Mercury:Return to Mercury:

The MESSENGER spacecraft (MErcury Surface(MErcury Surface, Space ENviroment, GE h i t dGEochemistry and Ranging)

Launched 2004: M bit iMercury orbit in 2011

Venus: Revolut

Orbital period = 225 days

Rotation period = 243 days

Rotation of Venus is retrogg

On Venus, the time from no

tion and Rotation

s

grade.g

oon to noon = 117 days

Venus is sometimes

Radius = 95

Mass = 82%

Surface gravity =

s called Earth’s twin:

% of Earth’s

% of Earth’s

= 90% of Earth’s

The surface of Venusclouds of su

Venus has 100% cloud covercover.

Its rotation speed can be pfound from radar signals which pierce the cloudswhich pierce the clouds (the same method used for Mercury, using Doppler effect).pp )

s is hidden from us by ulfuric acid.

The atmosphere of Vee at osp e e o Vea runaway gree

Dense and high-pre

Air pressure at the surface pressure on Earth (2/3

• 96.5% carbon dioxide 3 5% it (N )• 3.5% nitrogen (N2)

• 0.015% sulfur dioxide • almost no water vapor

enus is hot because of e us s ot because oenhouse effect.

essure atmosphere:

of Venus = 90 times air of a ton per square inch).

(CO2)

(SO2)r

CO2 is a greenhouse gas: soCO2 is a greenhouse gas: soGARGANTUAN green

Surface temperature = 733 (860 degrees Fahrenhei

Even hotter than Mercury!y

Temperatures drop very littTemperatures drop very littthanks to the thick atmo

Escape velocity for Venus p y

o Venus has ao Venus has a nhouse effect.

Kelvin it)

tle during the long nighttle during the long night, ospheric blanket.

= 10.4 km/sec

Venus was once cooler,Venus was once cooler,

Volcanoes produced large (all are gree

Air temperature rose.Air temperature rose.

CO2, SO

RUNAWAY grRUNAWAY gr

and may have had seas.and may have had seas.

amounts of H2O, CO2, S02

enhouse gases)

H2O evaporated from seas;

O2 released from seas, rocks.

eenho se effect!eenhouse effect!

The surface of VenThe surface of Venactivity but no

Because clouds are opaque surface ofopaque, surface of Venus has been

d i dmapped using radar, by the spacecraft Magellan.

Round-trip travel timeRound trip travel time gives us the distance:

d (t t )/2d=(t2-t1)/2c

nus shows volcanicnus shows volcanic plate tectonics.

Most of Venus is covered wMost of Venus is covered ware two large highland reg

Ishtar Terra (noAphrodite Terra (p (

with rolling plains but therewith rolling plains, but there gions:orth) ~ Australia(equator) ~ Africa( q )

Venus: many volcanoVenus: many volcanoMore than 1600 major volcaEstimated average age of cru

(older than Earth, much young

Perspective view of (Warning: vertical scale is(Warning: vertical scale is

es few impact craterses, few impact craters.anoes. ust = 500 million years ger than Mercury or Moon).

f Venusian volcanoes exaggerated by a factor of 10):exaggerated by a factor of 10):

About 1000 largAbout 1000 larg(more than Earth, mPerspective view o

Older craters have been o

ge impact cratersge impact craters much less than Moon). of Venusian craters:

obliterated by lava flows.

On the Earth, the cold rigid lithosphere isrigid lithosphere is broken into plates:

On Venus, the hot plastic lithosphereplastic lithosphere does not break:

No plate tectonics on Venus.

Levels of Vol

Earth: extremely active

Venus: mildl acti eVenus: mildly active

Moon: volcanically dead

Mercury: most likely volc

canic Activity

canically dead

Venus in extrImage returned

spacecraspacecra

reme closeup:d by Venera 13

aft (1982)aft (1982).

The interior of VenusThe interior of Venusthe E

Uncompressed density of Venus =density of Venus = uncompressed densit of Earthdensity of Earth = 4200 kg/m3.

Venus probably has a metal core andmetal core and rocky mantle, like the Earththe Earth.

s is similar to that ofs is similar to that of Earth.

Mars is a fairlyMars is a fairly

Radius of Earth =

Radius of Mars = 2

y small planet:y small planet:

2 x radius of Mars

2 x radius of Moon.

Mars is easy to ob

Mars can be seen at opposition whenopposition, when it is high in the sky at midnightat midnight.

Only a few wispy clouds, so the surface of Mars is easily seen (next page):

bserve from Earth.

Our current presen

Mars is currently host tspacecraft: Mars GlobOdyssey Mars ExpreOdyssey, Mars ExpreReconnaissance Orbiany planet other than home to the two Marshome to the two Mars(Spirit and Opportuni

nce near/on Mars:

to four orbiting bal Surveyor, Mars ess and Marsess, and Mars ter. This is more than Earth has. It is also

s Exploration Roverss Exploration Rovers ity).

Mars: Revoluti

Orbital period = 1.9 years

Rotation period = 24 hours

Rotation axis of Mars is tilt

Martian seasons similar to

ion and Rotation

, 37 minutes

ted by 25 degrees.y g

Earth seasons (only longer).

Mars has a tenuous atwater vapor an

Average air pressure on M0 6% of sea level pressur0.6% of sea level pressur

Escape speed from Mars isMercury; Mars is much cthe more massive molecu

95% carbon

3% nitrog

0 03% sul0.03% sul

tmosphere, with little nd few clouds.

Mars = re on Earthre on Earth.

s comparable to that of cooler, so it has retained ules like CO2.2

n dioxide (CO2)

gen (N2)

lfur dioxide (H O)lfur dioxide (H2O)

Little or no liquid

Boiling point of water decreBoiling point of water decreSea level: 100o Celsius Mt Everest: 75o CelsiusMt. Everest: 75o Celsius Mars: 5o Celsius = 278 Kelvin278 Kelvin

On Mars, liquid water can extemperature rangetemperature range.

d water on Mars.

ases as pressure dropsases as pressure drops.

xist only in a very limited

Little water vapor in th

There is little water vapor inThere is little water vapor inbecause ultraviolet light br

H2O + UV pho

Hydrogen escapes into spaceHydrogen escapes into space

Oxygen bonds with iron in t

he Martian atmosphere.

n the Martian atmospheren the Martian atmosphere reaks it up:

oton H2 + O

ee.

the soil, making rust.

Low density atmosphere imLow density atmosphere im(1) small greenhouse ef(2) large temperature sw(2) large temperature sw

Summer on Mars:High = 260 Kelvin Low = 200 Kelvin

Summer in Earth’s desertHigh = 310 KelvinHigh = 310 Kelvin Low = 290 Kelvin

mplies:mplies: ffectwingswings.

ts:

Martian

Martian clouds are mfrozen H2O2

n Clouds

made of ice crystals: , frozen CO2., 2

Martian

Icecaps at the north and somade of ice: froze

Icecaps shrink in sump

Icecaps

outh poles of Mars are also en H2O, frozen CO2.mmer, grow in winter., g

Mars has large volcaa s as a ge vo cavalley, but no p

Two hemispheres of Mars each othereach other.

North:recent volcanic activity (likrecent volcanic activity (lik

S thSouth:heavily cratered highlands

anoes and a huge rift a oes a d a uge tplate tectonics.

are very different from

ke Earth and Venus).ke Earth and Venus).

(like Moon and Mercury).

Topographicall map of Mars

BIGGEST VOLCANOOlymp

About the size of Arizona (~Last eruption about 300 mp

O in the Solar System: us Mons

~600 km across). million years ago: extinct.y g

Olympus Mons, like MauHawaii, is located over

Olympus Mons is 27 km tally p(height above ocean floor)

una Loa or Mauna Kea on a hot spot on the mantle.

l; Mauna Kea is 10 km tall ;). Both are shield volcanos.

BIGGEST VALLEY Valles M

Over 4,000 km long (LA to k d (G d Ckm deep (Grand Canyon:

A rift valley, caused when th

in the Solar System: Marineris

Boston), 200 km wide, 7 800 k l 30 k id )800 km long, 30 km wide).he crust was pulled apart.

MarsMars interior:

Robotic “rovers” havRobotic rovers havlook at

Spirit and OpportunityOpportunity(operated since J 2004)January 2004) are taking images and spectra of Mars procks.

Success!!Success!!

ve given us a close-upve given us a close up t Mars.

What have Spirit and OWhat have Spirit and O• Sent back spectacular pict

• Found sedimentary rocks tyevidence of having been s

Opportunity done for us?Opportunity done for us?tures:

that show chemical oaked in water.

Mars has two smalMars has two smalPhobos and

Phobos (“fear”): 28 kilometers long28 kilometers long.

Deimos (“panic”): ( p )16 kilometers long.

Irregular in shape, undifferentiated. Probably captured asteroidsasteroids.

ll irregular moons,ll irregular moons, d Deimos.

Random FacRandom FacPhobos orbits Mars in less th

Mars takes more than 24 hou(M ti ld Ph b(Martians would see Phob

Tidal bulge of Mars lags beha smaller orbit (Crush! In

ct of the Dayct of the Dayhan 8 hours.

urs for one rotation b i i t t i t!)bos rise in west, set in east!)hind Phobos, tugging it onto

n 40 million years).

Few closingFew closing

1) How do we know the maVenus?

2) Which one is denser: Mo

3) Can density of a planet bwater?water?

g questions:g questions:

ass of Mars? Mass of

oon or Earth?

be lower than density of


1) Name the major differenbetween Mars and the E

2) How dense is the atmosp

3) Are there volcanoes on M

4) Are there quakes on Mar


nces and similarities Earth.

phere of Mars?

Mars?

rs?


1) Name the major differenbetween Venus and the


3) What is the name of Ven

4) Are there volcanoes on V

5) Are there quakes on Ven5) Are there quakes on Ven


nces and similarities Earth.

phere of Venus?

nus’ moon?

Venus?

nus?nus?


1) Name the major differenbetween Mercury and thy

2) Name the major differenbetween Mercury and th

3) How dense is the atmosp3) How dense is the atmosp

4) What is the name of Mer)

5) Are there volcanoes on M


nces and similarities he Moon.

nces and similarities he Earth.

phere of Mercury?phere of Mercury?

rcury’s moon?y

Mercury?


1) Name the major differenMoon.

2) Is there still volcanic act


4) Is there water on the Mo

5) Why are there moonquak5) Why are there moonquak

6) Any other consequences


nces between Earth and

tivity on the Moon?

phere of the Moon?

oon?

kes?kes?

s of the Moon formation?

TtiTerrestria allPl t Planetspeople.physics.tamu.edu/depoy/astr101/Notes/lecture9.pdf · 2009-02-06 · Low-mass atoms escape firmass atoms escape fir massive ones. v esc v escapespeed

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