Mercury – Overview Innermost planet of the solar system; very similar to Earth’s moon. Just over 1/3 of Earth’s diameter (moon ~ 1/4) Lacks atmosphere Heavily cratered surface Lowlands flooded by ancient lava flows
Mercury Data Until recently, most of our knowledge of Mercury was based on photos and measurements by the Mariner 10 spacecraft (1974-1975). New spacecraft, Messenger (MEcurySurface, Space, ENvirnoment, GEochemistry, and Ranging mission) has conducted two flybys of Mercury and will make one more before it goes into orbit around the planet in March of 2011. Conduct close up observations.
Motions 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 not completely tidally locked. This gravitational influence is known as resonance. Rotates not once per orbit, but 1.5 times per orbit. Therefore, it’s rotational period is 2/3 its orbital period.
Mercury’s Motion Revolution ~ 88 days Rotation ~ 59 days Extreme day/night temperature contrasts exist on the planet: (-170°C) (430°C) Compared to Earth’s moon: (-170°C) (130°C)
Craters Heavily battered with craters of all sizes, including some very large basins.
Most are believed to have formed shortly after the heavy bombardment period.
Craters Largest crater on Mercury is the Caloris Basin. 1300 km (800 mi) – diameter. Mountain ranges present Ejecta blankets 600-800 km. from center of impact. Partially filled with lava flows.
Surface Features of Mercury “Discovery Scarp” Founded by the Mariner 10 spacecraft. Curved cliffs, known as lobate scarps, cover the surface and probably formed when Mercury shrank while cooling down.
Interior of Mercury Large, metallic core similar to all Terrestrial planets. 60% more dense than Earth’s core. Magnetic Field generated by core only 0.5% of Earth’s. Earth’s liquid outer core produces larger magnetic field compared to Mercury’s entire solid core.
Also note the difference in size and volume of Mercury’s mantle compared to Earth’s.
No plate tectonics on Mercury
Mercury’s History MERCURY “Winged Messenger of the Gods” Only heaviest elements could condense out. Condensation sequence Heavy bombardment left many impact craters. Stronger surface gravity than Earth’s moon. Cooling interior contracted deforming crust and creating lobate scarps.
Venus – Overview Considered Earth’s “twin”. Size and mass similarity. 95% diameter of Earth. Surface hidden by clouds (thick atmosphere). Hottest planet of the solar system
Atmosphere of Venus Extremely inhabitable. 96% CO2; only 3.5% N2 Other components (0.5%) include water vapor, sulfuric acid (H2SO4), hydrochloric acid (HCl), and hydrofluoric acid (HF). Thick clouds composed of acid droplets rather than H20 droplets like on Earth. Probes have studied atmosphere. Pioneer (USA) Stable circulation patterns with high-speed winds present. Slow rotation a factor?
Atmosphere of Venus Recall how the Greenhouse Effect warms the Earth. CO2 is transparent to light but opaque to infrared (heat) radiation. Energy can enter as light and warm the surface, but the surface cannot radiate the energy back to space easily. Earth ~ 0.04% CO2 Venus ~ 96% CO2 “Venusian” Greenhouse Effect even more dramatic than Earth’s. Temperatures on surface hot enough to melt lead. 470°C (880°F)
Motions of Venus All planets rotate counterclockwise as well as revolve in that direction. Exceptions: Venus, Uranus, Pluto Rotation ~ 243 days Revolution ~ 225 days Venus rotates clockwise. Possible explanations? Off-center collision with massive protoplanet. Tidal forces of the Sun on its molten core.
Surface Features of Venus Early radar maps penetrated the thick clouds of Venus and showed various surface features including mountains, plains, lava flows, and some craters. Pioneer (USA) Venera 3(Soviet Union) Magellan (USA)
Geology of Venus Scattered Impact Craters
Smooth Lava Flows
50% higher than Mt. Everest
Craters Nearly 1000 impact craters on surface. Believed to be more than Earth, but not nearly as many as Mercury and the moon. No very old craters, like we see on the moon. No erosion evident on the surface stable atmosphere could be a resulting factor.
Volcano Comparison Volcanism on Earth is commonly found along subduction zones (example: Rocky Mountains). Not found on Venus.
Volcanism on Venus All volcanoes on Venus are shield volcanoes. Fluid magma chamber exists , from which lava erupts repeatedly through surface layers above. Found above hot spots (example: Hawaiian Islands).
Volcanism on Venus Sapas Monsis one of the largest volcanoes on Venus. 2 lava-filled calderas 400 km (250 mi) diameter Lava flows
History of Venus VENUS “Goddess of Love” Venus has a complicated history and is still poorly understood. Solar wind interacts directly with atmosphere, creating a bow shock and ion tail. CO2 created during outgassing remained in atmosphere, where on Earth it dissolved in water. Any water that was present on the surface, evaporated rapidly Venusian Greenhouse Effect.
Mars – Overview The “Red Planet” Diameter ~ ½ of Earth’s. Similar seasons to Earth Mars axis tilted 25°, compared to Earth’s tilted 23.5°. Polar ice caps grow/shrink. Thin atmosphere, made of 95% CO2. Similar rotational period to Earth = 24 hours, 40 minutes
Atmosphere of Mars Very thin, only 1% of pressure at its surface compared to Earth’s. Haze and clouds exist.
Occasionally see dust storms that can cover the entire planet.
Atmosphere of Mars Most of the oxygen present on the planet does not exist in the atmosphere, but rather is bound in the rocks at the surface (oxides producing reddish color).
Atmosphere of Mars Martian atmosphere believed to be produced initially through outgassing. The loss of gases from a planets atmosphere depends upon the velocity of the gas molecules compared to the escape velocity of the planet: If the gas molecule velocity is greater than the escape velocity, gases will escape into space. Mars has lost all lighter gases and maintained the heavier ones like CO2.
Atmosphere of Mars Gases bound in the polar caps are returned each spring in spots and fans.
Geology of Mars Giant Volcanoes
Geology of Mars Northern lowlands: free of craters; filled with water at one point?
Southern lowlands: heavily cratered region.
Geology of Mars VallesMarinerisis a network of canyons 4000 km (2500 mi) long and up to 600 km (400 mi) wide. Deepest ~ 4 x Grand Canyon Long enough ~ NY to LA
Old feature, but shows the crust of Mars has been more active than the crusts of the moon or Mercury.
Volcanism on Mars Like Venus, all volcanoes on Mars are shield volcanoes. Olympus Mons Highest and largest volcano in the solar system.
Volcanism on Mars A great volcanic bulge in the crust of Mars is known as the Tharsis Rise. As large as the United States. Home to many smaller volcanoes, but on its summit lie three giants, and off to the NW edge, Olympus Mons.
Tales of Mars Early observers thought they saw canals on Mars. Believed to be created by an intelligent race. Led to H.G. Wells book, “The War of the Worlds” Fascination with Mars, its canals, and little green men lasted until July 15, 1965 when Mariner 4 conducted a fly-by of Mars, revealing a dry surface with no canals or Martian creatures.
Water on Mars? Two Vikinglanders touched down in 1976 and photographed exciting hints that water once flowed over the surface. More recent missions: Mars Global Surveyor (1997) Mars Odyssey (2001) Mars Express (2003) Mars Reconnaissance Orbiter (2005)
Water on Mars? No liquid water on the surface of Mars. Would evaporate due to low pressure. There is, however, evidence for liquid water in the past: Outflow channels from sudden, massive floods. Collapsed structures after withdrawal of sub-surface water. Valleys resembling meandering river beds. Gullies, possibly from debris flow. Central channel in valley suggests long-term flowing water.
Water on Mars? Photographs have been taken of eroded remains of a river delta in a unnamed crater in the old highlands. Flowed into deeper water, dropped off its sediment Mississippi River Delta into the Gulf of Mexico.
Much of the ice on Mars may be hidden beneath the polar ice caps. Radar has been able to penetrate down and map ice deposits hidden below the South polar region ~ enough water (90% pure) to cover entire planet to depth of 11 meters. Other probes found water ice not only mixed with soil as permafrost, but also as small chunks of pure ice, indicating there was once standing water that had frozen in place. Scientists propose ice was covered by a protective layer of dust and volcanic ash.
Water on Mars? Images have shown flow features and Hematite, a mineral that forms in water. Small spherical concretions of this mineral, indicating it must have formed in abundant water concentrations. Others show layers of sediments with ripple marks and crossed layers, indicating they were deposited in moving water. Chemical analysis of rocks show presence of sulfates, like Epsom salts along with Bromides and Chlorides. On Earth, these compounds are left behind when bodies of water dry up.
Water on Mars? Giant impacts by asteroids have created craters (Galle; “Happy Face”) and blasted Martian rock materials into space. Some are believed to have fallen to Earth as meteorites. Over 30 have been found and identified.
Moons of Mars Phobos Mars has 2 small moons, Phobosand Deimos. Believed to be captured from asteroid belt. Too small to pull themselves into spherical shape. Dark, grey with a low density. Close to Mars; orbit faster than Mars’ rotation. Deimos
History of Mars MARS “God of War” Mostly solid core, cannot produce magnetic field. Mars has water, but it is hidden. When humans reach Mars, they won’t need to dig far to find ice. Can use solar power to break water into Hydrogen (fuel) and Oxygen (breath of life) buried treasure?