Physics 320: Astronomy and Astrophysics – Lecture XII

NJIT

Physics 320: Astronomy and Astrophysics – Lecture XII

Carsten DenkerPhysics DepartmentCenter for Solar–Terrestrial Research

November 19th, 2003NJIT Center for Solar-Terrestrial Research

Problem 18.1

Mass[MMercury]

Radius[RMercury]

Moon 0.223 0.712Io 0.270 0.744Europa 0.148 0.643Ganymede 0.452 1.078Callisto 0.327 0.984Titan 0.409 1.055Triton 0.065 0.555Pluto 0.040 0.460


Problem 18.510

10

11

10

( ) 0.0016 s 1.92 10 d100 yr 1 yr

1.92 10 d47 d 1 d1 yr

2.4 10 yr( ) The main-sequence life-time of the Sun is about 10 yr

Earth is not likely to become fully synchronizedbefore

a Tt

t

tb

the sun becomes a red giant star


Problem 18.7

3

3M M EM

3ES

3ESM3

EM

( ) ˆ ˆ2cos sin with const.

F /F /

2.2

( ) Spring Tides:

or

Neap Tides:

M

M

M

a GMmRF i jrM rM r

rMM r

b F F

F F

F F


The Terrestrial PlanetsMercuryVenusEarthThe MoonMars


Mercury The four terrestrial

planets are small, rocky, and rotate slowly cf. moons

@ 0.34 AU Kepler’s laws break down Einstein’s theory of special relativity

Eccentricity of orbit: e = 0.206

Rotation period: T = 58.65 days Doppler effect

Orbital period: 87.97 days = 3/2 T

Mariner 10 found strong resemblance to the moon

Proximity to Sun and size very tenuous atmosphere


Mercury and Caloris Basin


3-to-2 Spin-Orbit Coupling Tidal Evolution Strongest tidal force

at perihelion Energy dissipation

due to friction

Circularization of Mercury’s orbit

3-to-2 spin-orbit coupling become instable

1-to-1 resonance of synchronous rotation


Venus Earth’s sister planet Mass: 0.82 MEarth Radius: 0.95 REarth Retrograde atmospheric

circulation (100 m/s at cloud tops near equator)

Hadley cells (“y”-shaped cloud pattern at equator)

Retrograde rotation of the planet

Sidereal rotation period: 243 days

Orbital period: 224.7 days


Phases


Atmosphere 96.4% carbon dioxide CO2 3.4% molecular nitrogen

N2 Traces of sulfur dioxide

SO2, water H2O, and clouds of sulfuric acid

Temperature 740 K and pressure 90 atm at base of atmosphere

Optically thick in the infrared

Volcanism and/or material delivered by comets and meteorites

2H O H OH


Greenhouse Effect


Surface


Earth Condensation of water

forms oceans early in the history of Earth

No conversion of liquid water into vapor!

Carbon dioxide dissolved in water or chemically bound, e.g., carbonate rocks

72% molecular nitrogen N2

21% molecular oxygen O2

1% water H2O Traces of argon AR,

carbon dioxide CO2, … Photosynthesis: CO2

organic materials + O2

Increase of greenhouse gases

Annual oscillation of CO2 due to vegetation cycles

Rainforest Ozone O3 layer


Structure and Atmosphere


Gravity Map of Earth


Methane EarthRecent evidence holds that methane (CH4) is second only to carbon dioxide (CO2) in creating a warming greenhouse effect but is easier to control. Atmospheric methane has doubled over the past 200 years, and its smothering potency is over 20 times that of CO2.


Seismic Activity


Moon Moon quakes due

to tidal strain (magnitude 1 on Richter scale)

The Moon’s “ringing” after being struck by meteorites

Craters and maria “seas”

Crust is thinner on near side


Structure and Formation


Radioactive Dating235 231 4 92 90 2

81/ 2

231 227 4 91 89 2

41/ 2

U Th He

and 7.04 10 yr

Pa Ac He

and 3.28 10 yr

, ,1/ 2

ln 2 with tA f A iN N e

, , , ,A f B f A i B iN N N N

, , ,1tB f B i A fN N e N

, , ,1B f A f B it

C C C

N N Ne

N N N


Mars “Canali” Giovanni

Virginio Schiaparelli (1835 – 1910)

Lowell (1855 – 1916) observatory, Flagstaff, AZ

Intelligent life on Mars? LGM? (H. G. Wells “War of the Worlds” broadcasted on October 30th, 1938)

Surface temperature: 140° C to 20° C

95% carbon dioxide CO2

2.7% molecular nitrogen N2

Atmospheric pressure: 0.001 atm

Water in layers of permafrost or frozen in polar ice caps

Polar caps predominantly “dry ice” frozen carbon dioxide

General relativity required to explain tilt of Mars spin axis

No large Moon!


Atmosphere and Volcanism


Deimos and Phobos


Ancient Streams and Dunes


(Happy) Faces and Hearts


Homework Class Project Continue improving the PPT presentation. Use the abstract from the previous assignment as

a starting point for a PowerPoint presentation. The PPT presentation should have between 5 and

10 slides. Bring a print-out of the draft version to the next

class as a discussion template for group work Homework is due Wednesday December 3rd,

2003! It would be good to have your final versions by then in order to have the final grades on December 10th, 2003.

Exhibition name competition (Final)!


HomeworkNo homework!!!The Final Exam will be due on

December 3rd, 2003 at the beginning of the lecture.

Please feel free to contact me with any questions concerning the final exam.

Documents

Physics 320: Astronomy and Astrophysics – Lecture XII