Lecture 10 Formation of the Solar System January 6c, 2014

Transcription

1 1 Lecture 10 Formation of the Solar System January 6c, 2014

2 2 Orbits of the Planets

3 3 Clues for the Formation of the SS All planets orbit in roughly the same plane about the Sun. All planets orbit in the same direction about the Sun. Most planets rotate in the same direction. There are distinct differences between Inner and Outer planets

4 4 Formation of the SS Nebular Theory Interstellar gas and dust contracts due to gravity Size >100 AU and ~2 M Sun Hydrogen and Helium and some trace elements Started ~4.6 billion years ago. Gas was very cold. Gravity pulling cloud together

5 5 Gravity Collapses Cloud Cloud collapses, rotates faster Conservation of Angular Momentum (e.g. ice skater pulls arms in, spins faster) Central core forms. Cloud flattens Centrifugal force stretches gas perpendicular to axis No such force to prevent collapse parallel to axis

6 6 Disk Forms Inner parts heated by gravitational collapse and by the young proto-sun Outer parts very cold Beta-Pictoris

7 7 Proto-planetary disk Beta Pictoris

8 8 Proto-planetary Disks Orion Nebula

9 9 The Solar Constant S Solar energy received at Earth 1400 Watts/m 2 (per unit time)(per unit area) For other planets: Solar constant at distance r (in AU) Mars: r = 1.5 AU Neptune: r = 30 AU It is MUCH colder in the outer regions than in the inner region S S S r 2 S Mars 0.44 S Neptune S S

10 10 Jupiter orbits at 5.2 AU. If the Earth receives 1400 W/m 2 of sunlight, how much does Jupiter receive? A. 37,900 W/m 2 B. 7,280 W/m 2 C. 269 W/m 2 D W/m 2

11 11 Jupiter orbits at 5.2 AU. If the Earth receives 1400 W/m 2 of sunlight, how much does Jupiter receive? A. 37,900 W/m 2 B. 7,280 W/m 2 C. 269 W/m 2 D W/m 2 S S r r S S r r Jupiter Jupiter Earth 1 AU 2 2 Earth Earth Jupiter 5.2 AU S Jupiter Earth 0.037S W/m 51.8 W/m 2 2

12 12 Condensation Temperature Condensation occurs when a gas cools and its molecules stick together to form a liquid or a solid Condensation occurs below a critical temperature that is different for different materials Metals and rocks: 1300 K to 1600 K Water, methane, ammonia ices : 100 K to 300 K

13 13 Planetesimals Form Material in cloud clumps and collides Form larger bodies through accretion Temperature high near proto-sun. Ices and gases in inner regions are vaporized Planetesimals cannot hold on to light elements; Lighter material moves outward Only heavier elements remain near Sun.

14 14 Planets Form Outer planets form from all material Planets capture mainly gases (H and He), because it was cooler in outer regions. only a little rock and metal because they have lower abundance Inner planets form from rock and metals. Warmer near sun Only heavier elements (rocks and metals) remained near Proto-sun

15 15 Temperature Distribution in the Solar Nebula

16 16 Planets are Differentiated Denser material moves inward in a liquid or gaseous planet Terrestrial planets were molten during early stages. Metals found closest to center Lighter rocky material remains in outer parts of planet

17 17 Sun Forms Sun obtains sufficiently high pressure and temperature in core to start fusion (converts Hydrogen to Helium) This is the time it officially becomes a star.

18 18 Solar System Today Planets still bombarded by left-over material Process took ~100 million years. Some debris still leftover (asteroids, meteoroids, and comets). 99.8% of the total mass is in the Sun. NASA movie

19 19 Movie of Solar System Formation

20 20 One explanation of why the planets near the Sun are composed mainly of rock and iron is that A. the Sun s magnetic field attracted all the iron in the young solar system. B. the proto-sun ejected iron-rich material from its surface. C. the high temperature near the proto-sun made it difficult for ices and gases to condense. D. the Sun s gravitational attraction pulled iron and other heavy material inward.

21 21 One explanation of why the planets near the Sun are composed mainly of rock and iron is that A. the Sun s magnetic field attracted all the iron in the young solar system. B. the proto-sun ejected iron-rich material from its surface. C. the high temperature near the proto-sun made it difficult for ices and gases to condense. D. the Sun s gravitational attraction pulled iron and other heavy material inward.