Astronomy The Planets and Their Moons

The Planets Solar System to not to scale or distance!

As of Summer, 2006… 3 Dwarf Planets: – Ceres (Asteroid Belt) Discovered in 1801 –At first, called a planet, then “demoted” when other asteroids discovered 2015: Dawn Mission – Pluto (Kupier Belt) Discovered in 1930 by Clyde Tombaugh –In 2006, reclassified as a Dwarf Planet 2015: New Horizons Mission – Eris (Kupier Belt) Discovered in 2003 Has 1 moon Bigger than Pluto; VERY far out from the Sun!

Planet Groupings Divided by the asteroid belt! The Inner Planets – Mercury – Venus – Earth – Mars The Outer Planets – Jupiter – Saturn – Uranus – Neptune – Pluto

What are the inner planets? Mercury Venus Earth Mars

What are the outer planets? Jupiter Saturn Uranus Neptune

Inner Planets vs. Outer Planets The Inner Planets: – Rocky crusts – Dense mantle layers – Very dense cores The Outer Planets: – Gaseous atmospheres (outer layer mostly made of hydrogen) – a lower density than Earth – ring systems inside their moons – large compared to Earth Pluto

What are some major differences between inner and outer planets? INNER PLANETS Rocky Dense Mantle Layers Very Dense Cores Mostly solid Have a crust OUTER PLANETS Gaseous Lower density than Earth Rings inside moons LARGE No real crust

The Inner Planets Mercury – no atmosphere – EXTREME temperatures Venus – no magnetic field – atmosphere of CO2 and sulfuric acid – temps near 475 C – atmospheric pressure is 90 times greater than on Earth Earth – Water and oxygen Mars – very thin atmosphere – 95 % CO2, 5% N and Ar – polar ice caps of frozen water and CO2 – dust storms

Venus and Mercury: Phases!

The Jovian (outer) Planets Jupiter – strongest magnetic field of all planets – gasses appear as bands – spots appear and disappear – radiates heat Saturn – fairly strong magnetic field – fewer gaseous bands – radiates heat Uranus – avg. temp is –200 C – methane gas is atmosphere – rotates on its side but magnetic field is not tipped Neptune – winds around 2000 km/hr – temps around –225 C – atmosphere is 74% hydrogen, 25% helium, 1 % methane

Neptune’s Orbit and Pluto Neptune is sometimes the farthest out “planet!” – Neptune and Pluto’s orbits cross each other Pluto – moon Charon is about ½ the size of the planet (1 of 3 moons!) – 70% rock, 30% water – temps from –235 C to –210 C – (not a “real” picture)

Planet Chart Comparison* *This is in your textbook - # moons is VERY “off” PlanetDist- ance To Sun RevolutionRotationDiameterMass (Earth = 1) Dens- ity # (major) Moons Mercury d.59 d.4, Venus d.243 d.12, Earth d.24 h12, Mars d.24 h 37 m6, Jupiter y.9 h 50 m142, Saturn1, y.10 h 14 m120, Uranus2, y17 h 14 m51, Neptune 4, y16 h49, Pluto5, y6 d 9 h2,

Largest Moons and Smallest Planets

Martian Moons Phobos and Deimos – small and irregularly shaped – Thought to have been captured asteroids (from the nearby asteroid belt that runs between Mars and Jupiter)

Jupiter’s Moons Jupiter has at least 50 moons Four largest (Galilean) – Io: active volcanoes; thin atmosphere – Europa: atmosphere; layer of ice – Ganymede: largest moon in the solar system; magnetic field – Callisto: some oxygen in atmosphere

Telescope View

Jupiter’s Moon’s Features

Saturn’s Moons and Rings Saturn has at least 62 moons – Titan – half rock, half frozen water; atmosphere Rings are made of mostly water ice and some dust

Saturn’s Satellites and Ring Structure

Uranus’, Neptune’s and Pluto’s Moons Uranus: at least 21 moons – Titania, Oberon, Umbriel, Ariel, Miranda – All have no atmospheres and many impact craters Neptune: 8 moons – Triton close to the size of Earth’s moon southern ice cap made of methane and ammonia ice volcanoes (??) very thin atmosphere Orbits backwards! Pluto: Charon (and 2 smaller – Nix, Hydra) Pluto – About ½ the size of Pluto – Really, they orbit each other!

Transits Transits – when one planet (or moon) crosses in front of another planet, moon, or the Sun, and shows up as a shadow. Transits seen from Earth – Mercury and VenusVenus – Why? Which 2 planets are between us and the Sun? Transit of Venus: June 8, 2004

Review: Planets and Moons What divides the inner and outer planets? What characterizes the inner planets? What characterizes the Jovian planets? Why couldn’t we live on our “sister planet”? Which 2 planets radiate more heat than they receive? Which planet is tipped on its side? Which planets occasionally flip-flop positions in the solar system? Using your planet-chart comparison, answer these questions: – Which planet has the fastest rotation AND the largest size? – Which planets have a smaller mass than the Earth? – Which planet has a density less than water? (less than 1) Which 2 moons are bigger than Mercury? Which planets do they belong to? What are the names of the Galilean moons? What are Saturn’s rings made from? Which two planets could we see cross in front of the Sun? Why not other planets?