Venus: Our Sister Planet

Transcription

1 Venus: Our Sister Planet Like Mercury close to the Sun. Maximum angle from Sun ~47 Hence seen at most for 3 hours before sunrise or after sunset. Venus reflects ~70% of its sunlight.

2 Property Earth Venus Radius 6378km 6052km 5.97x10 24 kg = 1 M E 0.82 M E Mass 4.87x10 24 kg = Average Density 5520kg/m kg/m 3 Gravity Earth s Escape Speed 11.2km/s 10.4km/s Average Temperature 290K / 17C 720K / 447C Eccentricity

3 Venus Retrograde Rotation Hard to establish rotation rate due to dense clouds (use Radar Doppler techniques) Sidereal rotation rate: 243 days Retrograde backwards with respect to Earth Tilt angle is Earth is 23.5 Large angle due to definition that Planets always rotate from East to West North is therefore below the plane of ecliptic.

4 Venus Strange Rotation

5 Consequences: Length of Day Slow backwards rotations means Solar Day (noonto-noon) is 117 Earth days. Sidereal rotation period is 243 Earth days. Venus year is 225 Earth days.

6 Why Retrograde Rotation? Don t really know! Possible that it was hit by a large object in its early evolution (like Earth?) which slowed it down to near zero. Venus has near perfect 5:1 synchronism between rotational and synodic orbital motion (117 days to 584 days). But no Earth-Venus gravitational interaction can account for this weird coincidence. This inhibits Earth based observations.

7 Cloudy Venus Best Earth-based photographs show an opaque planet in the visible wavelengths. But origin is not due to water vapour!

8 Venus in Ultra Violet Light Large fast moving clouds like our jet streams. Move around the planet in ~4 days. Hot ~ 730K 457C Sulphuric Acid cloud droplets!

9 The Atmosphere of Venus 96.5% Carbon Dioxide 3.5% Nitrogen Traces of Argon, water, CO, SO 2 No oxygen very different from Earth Clouds of sulphuric and hydrochloric acids, as well as Carbon Dioxide Atmosphere 90x more massive than Earth.

10 Earth Venus Comparison

11 The Greenhouse Effect Given its distance from Sun, why is Venus so hot? Carbon dioxide traps heat from the Sun. CO 2 clouds absorb ~99% of all radiation released from the surface. ~ 450C Temperature all over the planet (poles and equator) and little variation between day and night!

12 Greenhouse Effect on Earth and Venus

13 Why is Venus Atmosphere so Different from Earth s? If all the CO 2 that is either dissolved or chemically locked to minerals were to be released, Earth s atmosphere would be 98% CO 2! Ocean formation on Earth crucial. Postulate that Venus and earth had similar atmospheres in the past.

14 Atmospheric Evolution on Venus Venus was hotter than Earth due to it being ~30% closer to the Sun. More atmospheric water vapour on Venus. Water is a greenhouse gas too trapping more heat. Oceans never form. (CO 2 stays in atmosphere) Gets Hotter and Hotter :Runaway greenhouse effect. Water boils off planet (Hydrogen into space).

15 Venus has No Magnetic Field. Due to lack of rapid rotation which gives a dynamo effect on the molten core. No protection from solar wind of charged particles in upper atmosphere hence a heating/ionisation process.

16 The Earth s Magnetic Field Due to: Rapid Rotation of Liquid Conducting Core

17 Radar Images reveal two continents : Ishtar Terra and Aphrodite Terra. The Surface of Venus Babylonian and Greek versions of Latin Venus the Goddess of Love. Spatial resolution ~25km

18 High Resolution Radar image of Aphrodite Terra Magellan (False Colour)

19 Continents are Stable Terra are ~8% of Surface Area (~25% Earth) Sizes: Ishtar ~ Greenland, Aphrodite ~ Africa No Signs of plate tectonics on Venus.

20 Ishtar Terra: Maxwell Montes Mountain Range Crater Cleopatra meteoric yet with signs of lava flow Mountains ~14km high above deepest depressions. (~20km Earth)

21 Aphrodite Terra Ridges indicate surface buckling Stresses Lava channels common and 100 s km long

22 Evidence of Volcanism on Venus Lava domes ~25km across. Lava oozes out of surface forms a dome. Lava underneath withdraws leaving the crust to crack and subside.

23 Large Volcanoes Sif Mons (left) and Gula Mons Similar type to Hawaii local hot spot in crust. Summit collapses called a Caldera in these Shield volcanoes. Summits ~100km across! Evidence of continued volcanic on Venus activity (Radio emissions on eruption)

24 Sapas Mons, Pancake Domes, UV Venus

25 Craters on Venus Few small < 3km craters due to atmosphere Large Crater numbers < 10% of that on Moon Young planet or more erosion? Largest Crater: Mead

26 Craters on Venus

27 Soviet Landers: Venera 9, 10 (1975) Spacecraft melted in ~1 hour! Small young - little erosion - rocks and soil. Some volcanic basalt, others like granite.

28 ESA s Venus Express 2006 UV image South pole vortex: Day and Night Temperatures (IR)

29 The Turbulent and Chemically complex atmosphere of Venus (Thermal images)