The Solar System

Brief version of formation Frost line: all gaseous stuff is blown away by the sun leaving the terrestrial planets Jovian planets are beyond the frost line, so the gasses were protected

Terrestrial Planets

Earth Average distance from the Sun: 1.00 AU Radius: 6,378 km Mass: 5.97 × 1024 kg Avg. density: 5.52 g/cm3 Composition: rocks, metals Average surface temperature: 290 K Satellites: 1

Earth’s Structure Core – highest-density material, mostly Ni & Fe Mantle – moderate density, mostly Si, O, etc. Crust – lowest-density rock, granite & basalt Lithosphere – rigid outer layer of a planet, including crust and upper part of mantle Core can be divided into inner and outer core, where inner core is solid metal and the outer core is molten

Structure

Internal Heat Formation Geological Activity Caused by accretion and collisions during formation Also due to radioactive material Differentiation Convection and Cooling Differentiation means that denser material falls toward the center while less dense material rises to the surface Nearly all of the planet is actually solid. Only liquid part is just under the rigid lithosphere Convection must occur under the lithosphere and is responsible for geological activity Convection and the surface area / volume ratio are responsible for cooling As the planet cools, the lithosphere becomes thicker, making less room for convection, slowly choking off geological activity

Magnetic Field Caused by the motion of charged particles in Earth’s molten outer core Magnetosphere protects us from solar wind Aurora is caused when some particles do make it through the magnetosphere and collide with particles in the atmosphere The magnetic field is not as thick at the poles, so that is where this most often occurs

Shaping Earth’s Surface Cratering Volcanism Tectonics Erosion Meteor crater in Arizona. It is more that 1km across and 200m deep Volcanism: volcano in Alaska really important for Earth’s formation because without them we wouldn’t have an atmosphere Outgassing – when gas is released into the atmosphere from under Earth’s crust mostly CO2 released as well as H2O and H2S/SO2 outgassed water vapor rained down and formed the oceans and atmosphere tectonics – surface compressing makes mountains surface streching can make seas sheer can cause earthquakes result of mantle convection Presence of Plates (plate tectonics) may be unique to Earth Erosion piled stuff into layers, forming sedimentary rocks

Earth’s Atmosphere 77% N2, 21% O2 Protection X-rays are absorbed high up in the atmosphere Ozone absorbs UV Visible light gets through no problem

Earth’s Atmosphere Scattering Blue light is scattered more easily than red light Sky is blue because sunlight gets scattered to your eye from all directions Sun look red at sunrise/set because blue light gets scattered away Rayleigh scattering I~(lambda)^-4

Greenhouse Effect 5800 K H2O CO2 CH4 Visible Light IR Light 300 K Greenhouse gasses are gasses that are particularly good at absorbing IR radiation H2O, CO2, CH4 Remind of Wien’s Law IR Light 300 K Ground

Geologically Dead Objects

The Moon Average distance from the Earth: 384,000 km Radius: 1,700 km Mass: 7.3 × 1022 kg Avg. density: 3.35 g/cm3 Period: 29.5 days

Geological Features Lunar Maria Micrometeorites Lunar Maria are formed when a large impact struck the moon, fracturing the lithosphere. The mantle was heated up enough to melt by radioactivity. Molten lava flooded the crater. It is darker because of the Iron-rich composition of the mantle, which leaked through the lithosphere and flooded the crater. Micrometeorites constantly strike the Moon’s surface because there is no atmosphere. These objects pulverize the surface material, creating a very fine dusty layer on the Moon’s surface.

Mercury Average distance from the Sun: 0.39 AU Radius: 2,440 km = 0.38REarth Mass: 0.055 MEarth Avg. density: 5.43 g/cm3 Composition: rocks, metals Average surface temperature: 700 K day, 100 K night Satellites: 0 88 day orbit, 59 day rotation

Geological Features One giant crater called “Caloris Basin” Mercury is not that exciting. One giant crater called caloris basin Huge cliffs One giant crater called “Caloris Basin”

Mars Average distance from the Sun: 1.52 AU Radius: 3,397 km = 0.53REarth Mass: 0.11 MEarth Avg. density: 3.93 g/cm3 Composition: rocks, metals Average surface temperature: 225 K Satellites: 2

Perhaps it was more similar long ago Mars vs. Earth Similarities Differences Day is about 25 hours long Polar caps Axis tilted about the same More extreme seasons in southern hemisphere Polar caps contain CO2 Only about 1% of Earth’s atmosphere, which is CO2 Much colder Perhaps it was more similar long ago

Martian Geology

Martian Geology Polar ice caps Higher elevation of southern hemisphere Lack of craters in northern hemisphere Tharsis Bulge, Valles Marineris The Tharsis Bulge is a large elevated region home to some of the largest volcanoes in the solar system. Some believe it is actually one large volcanic system The Valles Marineris was discovered by the Mariner spacecraft (hence the name) and is a huge tectonic crack, probably associated with the Tharsis Bulge

Martian Geology Olympus Mons The largest volcano in the solar system Base covers an area equal to Arizona 26 km above average surface level, 3x the size of Mt. Everest

Water on Mars Today the surface temperature and pressure to too low for liquid water Polar caps Ground water Evidence of ancient H2O Dried Riverbeds Maybe not Signs of erosion “riverbeds” might actually have been formed by a surface collapse. Perhaps there is a lava tunnel or other flow under the surface that caved in.

What happened? Mars cooled, and the core solidified, preventing the convection necessary to maintain a magnetic field

Venus Average distance from the Sun: 0.72 AU Radius: 6,51 km = 0.95REarth Mass: 0.82 MEarth Avg. density: 5.24 g/cm3 Composition: rocks, metals Average surface temperature: 740 K Satellites: 0

Venusian Geology Craters, volcanoes, tectonics somewhat similar to Earth Coronae – bulges made by hot, rising plumes of mantle No plate tectonics

Venusian Atmosphere Atmosphere about 90x as thick as Earths Made up of about 96% carbon dioxide, but virtually no water Why should the atmosphere be different from Earth’s?

Why are the atmosphere’s different? Earth Venus Water rained into oceans CO2 dissolved into water and then formed into carbonate rocks Including the rocks, Earth has about as much carbon dioxide as Venus Lacking water Explains why there is more carbon dioxide in the atmosphere: cannot dissolve and become rock Where did the water go? UV light breaks up molecule

Runaway Greenhouse Effect

Life What is necessary?

A few examples Liquid Water Atmospheric Oxygen Climate Stability Planetary Size Must be large enough so it doesn’t cool too quickly, preventing tectonics Distance from Sun Liquid Water

The CO2 Cycle CO2 dissolves in rainwater This slightly acidic rain erodes rock and carries minerals to ocean Carbonate rock is formed, which sinks to the bottom of the ocean These rocks subduct and melt, releasing CO2 Volcanoes outgas CO2 The hotter it is, the more CO2 is pulled out of the atmosphere. If it gets hotter, the greenhouse effect is diminished, keeping things stable

Global Climate Change These are average temperatures There would be a much greater effect at the poles, melting polar caps

Global Climate Change CO2 in the atmosphere corresponds to the average temperature We need to reduce the amount of CO2 we release into the atmosphere Don’t want a runaway greenhouse effect