1

Terrestrial Planets • Periods of revolution• Distances from Sun• Size• Mass• Density• Composition• Surface temperature

2

Planetary Orbits and configurations

When it is possible to see Mercury?

“Evening star” or “morning star”

Every 2 months 1-2 hrs per night

3

Max angular distance Aphelion 70 x106 km

Perihelion 46 x106 km 4

Sidereal Period

Synodic Period

Mercury’s synodicperiod : 116 days

1/Sid = 1/Syn + 1/365.25

Mercury’s sidereal period :

88 days

2

Max angular distance from Sun

Orbital Motion

Revolution around Sun = 88 days = 0.24 yr

Distance from Sun = 0.39 AU

Orbital speed = 48 km/s

Eccentricity = 0.206

Inclination of the plane of orbit

Rotation of Mercury on its axis

Doppler Effect

Speed of rotation v

T = C / v = 59 days

Rotation W to E

1 ½ rotation about its axis for 1 orbital period

59/88 ~2/3

Sun’s gravitational influence

• Mass ~1/18 Mass of Earth• Diameter = 4878 km• Density = 5.4 g/c cm• Surface gravity ~3.7 m/s2

• Structure• Magnetic field• Tidal Bulge• Atmosphere, Water• Surface Temperature (800 F to -300 F)

MercuryMercury’s Interior

DensityComposition

Magnetic Field

3

A Model for the Origin of Mercury’s Large Metallic Core Surface •Using Earth-based telescopes

•Mariner 10 (1974-1975)

•No evidence of plate tectonics

•Old

•Larger gravity than Moon

•Craters (100 m)

•Plains•Intercrater Plains•Smooth Plains

•Great scarps (cliffs)

•Atmosphere

Mercury

Mariner-10 photographed Mercury's meteorite-battered surface.

Craters

4

Intercrater plainsSmooth plains

Scarps (cliffs) 16

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Venus Clouds

Image of Venus obtained with the Galileo satellite

Radius = 6052 km

Atmosphere:•Carbon dioxide•Nitrogen

Brightness: reasonsVisibilityView through a telescopeMass, Radius, DensityAtmosphere and surface features

5

17

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Global viewof the surface of Venus :

Map based on radio-observation

Rotation of Venus on its axis

Doppler Effect

Speed of rotation

T = C / v = 243 days

Retrograde rotation E to W

1 revolution around Sun –226 days

W to E W to E

W to E

W to E E to W

W to E

Prograde rotation

Retrograde rotation1 day on Venus is ½ of one year on Venus

(Don’t confuse with retrograde motion)

Orbital Data

• Distance from Sun– 0.723 AU

• Eccentricity of orbit• Inclination of orbit• Orbital period

– 224.7 days• Rotational period

– 243 days)

Physical Parameters

• Mass• Diameter• Density• Surface Gravity• Average surface

temperature – 460 C = 860 F = 733 K

6

The Earth Atmosphere

•Basic Facts•Pressure exerted at see level•Total mass

•Structure of the atmosphere

•Atmospheric composition at the Earth’s Surface

•72% N 21% O 1% Ar•Water, CO2•Dust, water droplets

Atmosphere•Surface temperature:

•600-800 F•Temperature profile

•Horizontal: very uniform•Vertical

•Pressure at surface•92 atm; •1 atm at 50 km

•Density •Composition

•Carbon dioxide•Nitrogen

•Clouds (45-60 km)•Sulfuric acid•Not very dense but very thick•Absorb most of sun light•Strong winds (350 km/h)•Wind drops toward surface

The Green House Effect

Venus: reflects 80% Earth reflects 30 %

Venus: 2.5 % reaches the surface

Earth absorbs more, Venus surface temperature much higher

Clouds made of CO2

Exploring Venus

•Venera Series: first pictures of Venus’ surface•Vast flat regions• broken rocks, •“orange world”• real color – dark gray (Earth’s ocean floor)• silicate rocks

• Magellan spacecraft: radar maps•Low and high regions

•Vertical crustal distortion•Few impact craters•Recent massive lava flow •~500 volcanoes•No tectonic activity

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• Similarities– Mass, size, density– Initial chemical composition (N, CO2)– Climates at first – Surface

• Differences– Rotation around Sun– Present atmospheres: composition, pressure, temperature– Surface temperature– Water– Magnetic field

Venus and Earth Venus ExpressFirst European mission 11.09.2005

AtmosphereAre the volcanoes active?Why Venus is so different from Earth now?

220 million euro,5 months

486 Earth’s days