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The Other Terrestrial Planets Mercury

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The Other Terrestrial Planets Mercury The Other Terrestrial Planets Mercury Doppler Effect Rotation and Revolution Surface Features History View from Earth Earth Mercury Semi-major Axis 1 A.U. 0.387 A.U. Inclination 0° 7° Orbital period 1.000 tropical year 87.97 days Orbital eccentricity 0.017 0.206 Rotational period 23 h 56 min 4.1 s 58.65 days Tilt 23° 27’ 0° Radius 6378 km 2439 km Mass 5.97 x1024 kg 3.30 x 1023 kg Bulk density 5.52 g/cm3 5.43 g/cm3 Atmosphere N2, O2 trace Na, K, H2, He Albedo 0.40 0.06 Surface temperature 250-300 K 100-700 K Escape speed 11.2 km/s 4.3 km/s Magnetic moment (equator) 8 x 1010 G.km3 4.8 x 107 G.km3 Viewing Mercury from Earth Phases of Mercury can be seen best when Mercury is at its maximum elongation Measuring Mercury’s Rotation: the Doppler Effect The light of a moving source is blue/red shifted by Dl/l0 = vr/c l0 = actual wavelength emitted by the source Blue Shift (to higher Red Shift (to lower Dl = l - l0 frequencies) frequencies) wavelength change from the Doppler vr effect vr = radial velocity Example 1 of the Doppler Effect Earth’s orbital motion around the Sun causes a radial velocity towards (or away from) any star. Example 2 of the Doppler Effect Take λ0 of the Hα (Balmer alpha) line: λ0 = 656 nm Assume, we observe a star’s spectrum with the Hα line at λ = 658 nm. Then, Δ λ = 2 nm. -3 We find Δλ / λ0 = 0.003 = 3 x 10 Thus, vr/c = 0.003, or vr = c Δλ / λ0 = 300,000 km/s x 0.003 = 900 km/s Because the value is positive, the line is red shifted, so the star is receding from us with a radial velocity of 900 km/s. Doppler Effect: Planetary Rotation Radar is bounced off the two sides of the planet. The Doppler shift is used to determine the rotation velocity. With the measurement of the circumference of the planet, the rotation period can be calculated. Rotation and Revolution of Mercury Like Earth’s Moon (tidally locked to revolution around Earth), Mercury’s rotation has been altered by the Sun’s tidal forces, but it has not locked into a 1:1 spin-orbit resonance. It is in a 3:2 resonance. Revolution period = 3/2 times rotation period. Revolution: ≈ 88 days, Rotation: ≈ 59 days Extreme day-night temperature contrast: 100 K (-173 oC) – 600 K (330 oC) Spacecraft Exploration of Mercury Mariner 10: flew by Mercury, 1974–75 Spacecraft Exploration of Mercury The Messenger spacecraft was launched in August 2004. It flew by Mercury in January and October, 2008 and September, 2009. It was put in orbit around Mercury in March, 2011. Mercury Mercury is very similar to the Moon in several ways: • Small; no atmosphere • Lowlands flooded by ancient lava flows • Heavily cratered surfaces Lobate Scarps Mariner 10 Messenger Curved cliffs, several hundred km long and up to 3 km high, probably formed when Mercury shrunk while cooling down Caloris Basin The Caloris Basin, is a very large impact feature that is not as completely flooded as the mare of the Moon The Surface of Mercury Weird terrain was found on the opposite side of the planet from the Caloris Basin . Weird terrain was subsequently found on the far side of the Moon opposite large basins. History of Mercury 1) Formed about 4.6 million years ago 2) It melted from impact energy and cooled slowly 3) Differentiation to form metallic core and rocky mantle 4) Major impact might have melted and ejected much of the mantle 5) Interior shrank, crumpling the solid crust 6) Massive meteorite bombardment Cratering; lava flows Venus Rotation Atmosphere Surface Features History Earth Venus Semi-major Axis 1 A.U. 0.723 A.U. Inclination 0° 3° 23’ Orbital period 1.000 tropical year 224.7 days Orbital eccentricity 0.017 0.007 Rotational period 23 h 56 min 4.1 s 243.01 days—retro Tilt 23° 27’ 117° 18’ Radius 6378 km 6052 km Mass 5.97 x1024 kg 4.87 x 1024 kg Bulk density 5.52 g/cm3 5.24 g/cm3 Atmosphere N2, O2 CO2, N2 Albedo 0.40 0.76 Surface temperature 250-300 K 700 K Escape speed 11.2 km/s 10.4 km/s Magnetic moment (equator) 8 x 1010 G.km3 >4 x 106 G.km3 The Rotation of Venus Almost all planets rotate counterclockwise (prograde rotation), i.e. in the same sense as orbital motion. Exceptions: Venus, Uranus and Pluto Venus rotates clockwise (retrograde rotation), with a period slightly longer than the orbital period. Possible reasons: . Tidal forces of the Sun on a molten core . Off-center collision with a massive protoplanet Long-Distance Observations of Venus Dense atmosphere and thick clouds make the surface impossible to see The surface temperature is about 730 K – hotter than Mercury! Spacecraft Exploration of Venus Soviet Venera probes landed on Venus from 1970–1978 The Magellan spacecraft mapped Venus using synthetic aperture radar from 1990-1994 The Atmosphere of Venus Venus’s atmosphere is very dense (~100 x pressure of Earth’s) Solid cloud bank 50– 70 km above surface hiding it from view Atmosphere is mostly carbon dioxide; clouds are sulfuric acid The Atmosphere of Venus Venus is the victim of a runaway greenhouse effect – it just kept getting hotter and hotter as infrared radiation was reabsorbed The Surface of Venus The surface is relatively smooth: 60% of North the terrain lies within 500 m of the mean planetary radius Two continent-like features: Ishtar Terra Ishtar Terra and Aphrodite Terra No plate tectonics Lakshmi Planum Maxwell Montes Mountains, craters, many volcanoes and large lava flows 0° 90° 180° 270° Aphrodite Terra Beta Regio Alpha Regio Chasma region The Surface of Venus The only direct surface information we have about Venus came from a few Venera spacecraft Synthetic aperture radar images made by the Magellan spacecraft give us the greatest detailed information about surface features Venera 13 photograph of surface of Venus: Colors modified by clouds in Venus’ atmosphere After correction for atmospheric color effect: The Surface of Venus Volcanoes on Venus Above: Sif Mons Right: Gula Mons Volcanic Features on Venus Aine Corona Coronae: Circular bulges formed by Baltis Vallis: 6800 km long volcanic activity lava flow channel (longest in the solar system!) Lava flows Pancake domes: Associated with Some lava flows volcanic collapsed after activity forming molten lava drained coronae away Craters on Venus There are nearly 1000 impact craters on Venus’ surface Surface not very old. There is no water on the surface; it has a thick, dense atmosphere No erosion Craters appear sharp and fresh Craters of Venus Venus’ largest impact crater, named after Margaret Mead Venus’ Magnetic Field and Internal Structure There are no measurements available that would give clues to internal structure. However, because it is similar to Earth in size and density, it is reasonable to assume that it has a similar internal structure. There is no magnetic field, probably because its rotation is so slow. This would be consistent with the magnetohydrodynamic model. A History of Venus . Complicated history; still poorly understood. Solar wind interacts directly with the atmosphere, forming a bow shock and a long ion tail. CO2 produced during outgassing remained in the atmosphere (on Earth: it dissolved in water). Any water present on the surface rapidly evaporated feedback through the enhancement of the greenhouse effect . Heat transport from core mainly through magma flows close to the surface ( coronae, pancake domes, etc.) Mars Earth Observations Surface Features Volcanism Craters Water Polar Caps Atmosphere Satellites Earth Mars Semi-major Axis 1 A.U. 1.524 A.U. Inclination 0° 1° 51’ Orbital period 1.000 tropical year 1.881 tropical year Orbital eccentricity 0.017 0.094 Rotational period 23 h 56 min 4.1 s 24 h 37 min Tilt 23° 27’ 25° 12’ Radius 6378 km 3397 km Mass 5.97 x1024 kg 6.42 x 1023 kg Bulk density 5.52 g/cm3 3.94 g/cm3 Atmosphere N2, O2 CO2, N2,H2O Albedo 0.40 0.16 Surface temperature 250-300 K 210-300 K Escape speed 11.2 km/s 5.0 km/s Magnetic moment (equator) 8 x 1010 G.km3 2.5 x 107 G.km3 Earth Observations of Mars Can see polar ice caps that grow and shrink with the seasons. Earth Observations of Mars • Changing polar ice caps are frozen carbon dioxide (dry ice); water ice is permanently frozen • Shifting dust cover makes the surface look like it is changing • Frequent dust storms, with high winds • We did not understand that dust and winds were responsible for changing features before spacecraft observations Orbital Exploration of Mars 1971—Mariner 9 1976—Viking 1 and 2 1993—Mars Observer (failed) 1997—Mars Global Surveyor 2001—Mars Odyssey 2003—Mars Express (ESA) 2006—Mars Reconnaissance Orbiter Interior of Mars . No seismic studies have been done . From the behavior of the crust, it is estimated to be 100 km thick . There is no magnetic field, so the core is probably not metallic, or not liquid, or neither liquid nor metallic Surface Features Utopia Planitia Chryse Planitia Elysium Mons Olympus Mons Tharsis Montes Valles Marineris Hellas Basin Argyre Basin Landing Sites Phoenix Curiosity Surface Spacecraft Exploration of Mars Viking landers arrived at Mars in 1976. The Surface of Mars Both Viking landers landed in low-latitude northern plains They photographed a rocky surface The red color is caused by hydrated iron oxides Viking 1 image The Surface of Mars Viking 2 image Shows frost which quickly evaporates after sunrise The Surface of Mars Sojourner rover was deployed on Mars in 1997 during the Pathfinder mission.
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