Distance Determination

Transcription

1 Mercury & Venus Radar, doppler shift, and rotation General orbital properties Tidal effects of Mercury Surface composition of Mercury Origin of Mercury MESSENGER mission Rotation of Venus Clouds of Venus Venusian topography Craters Tectonic features

2 Mercury Discussed Thus Far Closest planet to the Sun (0.4 AU) Negligible atmosphere Heavily cratered surface Unusually large iron core Weak magnetic field

3 Distance Determination Radar: radio waves are bounced off of an object Distance is determined by the time it takes for the signal to bounce off of the object & return to the radar source

4 Speed The Speed is determined through doppler shift, which relates frequency/wavelength with speed

5 Rotation determined via broadening of radar signal

6 Mercury & Venus Inferior Planets: planets with orbits smaller than that of the Earth Both planets are observed in the morning or evening sky (i.e., leading or trailing the Sun in the sky) Eastern/Western Elongation the maximum distance the inferior planets appear to get in the sky from the Sun

7 Tidal Effects Mercury Mercury year = 88 Earth days Mercury day = 59 Earth days The orbit of Mercury is eccentric! Perihelion = 0.31 AU! Aphelion = 0.47 AU Rotation period minimizes the tidal dissipation near perihelion

8 Surface Composition Color & reflectivity are indicative of igneous silicate rocks & perhaps metallic rock Age of the surface is undetermined

9 Surface Composition, cont. Polar cap: permanent deposit of water or other frozen volatiles in the cool polar regions of the planet Discovered via radar mapping of Mercury. These regions have high radar reflectivity

10 Surface Composition, cont. Tilt of rotational axies with respect to the ecliptic plane = 0, thus polar regions receive little sunlight But where did the volatiles come from? Impacts with comets? Outgassing?

11 Surface similar in appearance to the Earth s Moon

12 Surface Features, cont. Caloris Basin Mare Orientale Caloris Basin - largest structure on Mercury (1000 km), created by an impact with an asteroid. Circumference of Mercury is 7700 km. A similar feature is seen on the western edge of the Moon - Mare Orientale.

13 Surface Features, cont. Scarp radial to Caloris Basin Jumbled Terrain Opposite Caloris Basin on Mercury The impact that resulted in the Caloris Basin generated compression on the surface of Mercury

14 Origin of Mercury Created with a disproportionately large core via a collision with a large, planet-size asteroid If this happened after differentiation, much of the crust material could have been lost

15 The Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) Launch - August 3, 2004, Mission End Date - March 2012 objectives - to characterize the chemical composition of Mercury's surface, the geologic history, the nature of the magnetic field, the size and state of the core, the volatile inventory at the poles, and the nature of Mercury's exosphere and magnetosphere over a nominal orbital mission of one Earth year. 2 flybys will gather information for planning main mission

16 Venus Discussed thus far Second planet from the Sun (0.7 AU) Thick atmosphere composed primarily of CO 2 High surface temperature Clouds of Sulfuric Acid Radar-constructed map of Venusian Surface

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18 Retrograde rotation Long sidereal day = -243 Earth days Solar day = -117 Earth days Rotation of Venus

19 UV Image Clouds Highly reflective (75%) Cloud temperature (-35 C) Upper atmosphere Clouds rotate around the planet in four days due to! rotation of planet! thin upper atmosphere! heating by solar radiation Lower atmosphere! Wind speed 0-2 m/s! Coriolis is negligible slow rotation of planet! Hadley cells air traveling via convection from equator to poles

20 Topography Contrast between high & lowlands is not as dramatic as it is on Earth

21 Topography Contrast between high & lowlands is not as dramatic as it is on Earth

22 Surface Features: Craters on the Venusian Surface 1000 impact craters Sizes: km! No large craters: surface doesn t date back to heavy bombardment period! No small craters: they burn up in the thick atmosphere Craters are pristine: low erosion rate

23 The Tick Crater

24 Plate Tectonics on Earth

25 Surface Features: Tectonic Features Created via tension or compression in the crust of the planet No well-defined tectonic plates

26 Radar image of Venus (Global) Band near equator: crustal compression

27 Surface Features: Pancake Domes 45 km in diameter 2 3 km high Created when lava is belched up all at once

28 Surface Features: Coronae Circular/Oval Features 100s 1000s km across Characterized by concentric & radial tectonic patterns &, often, by associated volcanic eruptions What are they?! failed hot spots! developing hot spots Low central dome

29 The Surface Several Venera landers lasted for up to 2 hours on the Venusian surface Loose rocks Basalts: produced by rapid cooling of lava

30 Runaway Greenhouse Effect: Could Venus have been more Earth-like in the past? 1) At 0.72 AU, Venus receives a higher flux of solar radiation 2) Evaporation of Oceans! water vapor (greenhouse gas) 3) Higher temperature! more evaporation 4) Water vapor rises to high elevations in a hot atmosphere 5) Water vapor + sunlight! Hydrogen + Oxygen 6) Light Hydrogen escapes 7) Oxygen combines with rocks

31 The Venusian Surface Crater counts = 500 million year-old surface Possible Explanation about 500 million years ago, lava broke through the thick lithosphere & covered the planet! the lithosphere resealed afterward! Note: this is very speculative!!!