Solar System. Sun, 8 planets, hundred moons, thousand.dwarf.planets million asteroids, billion comets etc.

Transcription

1 Solar System Sun, 8 planets, hundred moons, thousand.dwarf.planets million asteroids, billion comets etc.

2 Comparative Planetology Compares planets and other solar system bodies to help understand how they formed and evolved Diameters: 10 times Earth=Jupiter & 10Jupiters=Sun Distances: Sun-Earth=8light-minutes & Sun-Jupiter=1Hour

3 Solar System Looks Like a Disk As the planet s distance from the sun increases; circumference of orbit increases & velocity decreases so period of orbit increases Planets revolve in orbits that are tilted less than 7 to sun s equator Planets ALL orbit in same direction As Sun rotates

4 Obliquity of Rotation Axes Most planets rotate counter-clockwise Most planets rotation axis is perpendicular to ecliptic plane Sun s rotation axis tilted by 7 But why is Uranus tilted ~90? Why does Venus rotate retrograde=clockwise?

5 Two Kinds of Planets Planets are relatively isolated Terrestrial planets- 4 inner planets Jovian planets 4 outer planets

6 Terrestrial Planets Mercury, Venus, Earth, Moon, Mars, Located closer together near sun Smaller, denser, rocky Solid surface & Weak magnetic field Little or no Hydrogen and Helium Few moons, no rings

7 Jovian Planets Jupiter, Saturn, Uranus, Neptune Widely spaced in outer solar system Larger, gaseous, containing Hydrogen & Helium like Sun Dense atmosphere with no surface & Strong magnetic field Many satellites, ring systems

8 Average Density of Planets Density is mass divided by volume How heavy per volume Terrestrial Planets more dense than Jovian gas giants Problem is moon is not as dense (3.4gm/cm 3 ) as Earth (5.5)

9 Interplanetary Matter Planets have cleared their orbits, but there s debris leftover Comet & Asteroid dust ~40,000 tons/year falls to Earth Seen as Zodiacal Light

10 Asteroids = Minor Planet Rocky, smaller than the moon; larger than 100meters diam. Not enough gravity to pull them into spherical shape Ceres~1000km diam; Vesta~500km; 15>250; ~million >1km Movie of Eros

11 Asteroid Belt Asteroids, Near Earth Objects, Comets Millions of asteroids generally orbit between Mars and Jupiter Over 444,080 with good orbits Named by discoverer 1 named after UVic and 14 others named after UVic people

12 Kuiper Belt Region More than 1000 icy objects like Pluto in Kuiper 30-50?AU

13 Comet: Hale-Bopp 1997 Dirty snowball; leftover from formation of solar system Nucleus 1-10km Ices melt/steam when close to sun Forms million km long tail

14 Oort Cloud Trillions of comets in orbits of ~a light year 1000 times further than Kuiper belt

15 Meteorites Peekskill meteorite or fireball 1992 New York; Bright as full moon Meteorite on ground, meteor in air and meteoroid in space Pinhead sized rocks burn up ~80km up Some leftover from formation of Solar System

16 Radioactive Dating Clocks start at time of solidifying and reset by melting 238 U radioactive decays to 234 Th 206 Pb With half-life of 4.5billion years We have rock samples of the Earth, Moon, Mars, meteorites All date to maximum of ~4.6 Billion years Time of formation of Solar System

17 Spacecraft Missions Show New Worlds Mercury 1 flyby& 1 orbiter Venus many flyby, 4.orbiters Mars many orbiters, 4.landers & 4 rovers Jupiter, Saturn, etc. 4 flyby & 2 orbiters

18 Gravity Assist Throws ball on parked car Throws ball on moving car Throws ball on orbiting car

19 Pale Blue Dot Voyager 1 looks back and takes a picture of the Earth Gives us perspective

20 What are the characteristic properties of the solar system that a theory of its formation needs to explain: a) Planets isolated in space=cleared orbit b) Disk shape of solar system- small orbit inclination; prograde circular motion; same tilt&direction of rotation axes (almost) c) Jovian/Terrestrial planets: low/high density, huge/small atmospheres, fast/slower rotation rates, many/few moons & rings and Space Debris icy comets, rocky asteroids, meteoroids, Kuiper Belt d) Earth, Moon, Mars, Meteorites, Sun; all 4.6 billion years old e) All of the above

21

22 Trans-Neptunian Objects Objects which orbit the sun beyond Neptune

23 Impact Crater Formation Impactor has velocity 10 times rifle bullet Releases energy 10 times equal mass of dynamite Impactor vaporized when temperature reaches millions K Shock wave forms shocked quartz found only in impacts Rebound can launch rocks without destroying them

24 Rocky Surfaces Saturated with Craters Planets formed from many meteorite impacts Circular craters due to explosion caused by impact Solar System Full?

25 Erosion of Craters Craters hidden by: 1. Volcanoes lava flows 2. Continental drift 3. Erosion by atmosphere 4. Oceans

26 Younger Terrain = Fewer Craters The larger the terrestrial world; the more internal heat it will retain = higher temperature in core The higher temperature; more geologically active so more craters are covered = fewer craters showing Older terrains = more craters

27 Comet Impacts on Jupiter Painting shows Jul94 impacts of Comet Shoemaker-Levy 9 HST photo from 20Jul09 Comets deposit ice Heating planet

28 03Jun10 Jupiter Impact Last June Jupiter became a little more massive Two amateur astronomers recorded the impact 2009 impact left scar Notice missing SE belt

29 Planetary Magnetic Fields Jovian planets plus Earth have magnetic fields Various directions and strengths and offsets

30 Planetary Dynamo Conducting, convecting/circulating, rotating core generates magnetic field Earth: Iron core; Jupiter: liquid metallic hydrogen Uranus, Neptune: water with ions

31 Magnetometer Measures the strength & direction of Magnetic field Can probe the interior of the planet

32 Elemental Abundances Element determined by number of protons=atomic number Neutrons determine Isotope Elemental abundances on Earth Not the same as in stars, Jupiter, Saturn

33 Elements Forged In Star s Cores You are made of star dust Stars have died so you may live

34 Chondrules Many meteorites contain small glassy inclusions Formed by rapid melting and solidified in hours Chondrules date from formation of Solar System

35 Outgassing Water, carbon dioxide, sulfur dioxide, nitrogen released by volcanoes Forms atmosphere

36 Angular Momentum Problem The protosun rotates rapidly and has huge convection cells so it generates a strong magnetic field The magnetic field tries to accelerate the disk and solar wind, slowing rotation by magnetic braking Observations of stars with known ages in Hyades etc. show that the older stars rotate more slowly

37 Late Heavy Bombardment Late Heavy Bombardment second surge in impacts When Jupiter, Saturn, Uranus, Neptune change orbits scattering planetesimals?

38 Debris Disk After the dense disks that form planets Cold disks of dust are left Made from asteroid collisions & comet s tails

39 Comet NEAT 29Jan & 2Feb03 Dirty snowball or maybe icy mud ball is better Nucleus ~ 10km Tail ~1,000,000km to 1 astronomical unit Very eccentric elliptical orbit

40 Atmospheric Escape More massive planets have higher Escape Speed Hotter planets have faster moving air molecules Heavier molecules move more slowly Atmosphere can leak into space over eons of time