Origin of the Solar System Astronomy 311 Professor Lee Carkner Lecture 8.
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Origin of the Solar System Astronomy 311 Professor Lee Carkner Lecture 8
Quiz 1 Monday Covers lectures 1-8 and associated readings About half multiple choice (~20 questions), half short answer/problems (~4 questions) Study: Notes Can you write a paragraph explaining each major concept? Exercises Can you solve all the exercises with no resources? Readings Can you do all the homework with no book and Quizdom questions with no notes? Bring pencil and calculator! No sharing!
The Solar System Questions When did it form? Why does it have structure?
Structure of the Solar System The solar system has three distinct regions Mercury, Venus, Earth, Mars, Asteroids Jupiter, Saturn, Uranus, and Neptune Trans-Neptunian region Made of ice
Where Did the Solar System Come From? We can’t look back in time to see how the Sun and planets formed, but we can look at young stars that are forming today
Star Formation Stars are formed in clouds of gas and dust when a clump of material starts to contract The mutual gravity of the particles in the clump causes the contraction to continue Conservation of angular momentum makes the clump spin faster Rapid rotation causes the outer layers to form a disk
Circumstellar Disks Disks are fairly cool and can be detected with infrared and millimeter telescopes Disks are common around young stars
From Disks to Planets Where does the disk go? A disk has more surface area than a group of planets with the same mass, so it radiates more light Disks you can see, planets you can’t
How Do Planets Form? There are 4 stages of planet formation 1 2grains stick together to form planetesimals 3 4gas and leftover planetesimals are cleared from solar system
What Was the Solar Nebula Made of? Solar Nebula -- From studying meteorites and star forming regions we hope to discover what the solar nebula was made of Gas -- Dust -- made of rock (silicates), metal (iron) and ices (water, methane, ammonia, carbon dioxide)
Accretion of Grains Grains get larger by sticking together and settle to the center of the disk Eventually the grains form into larger bodies (a few km in size) called planetesimals At the end of this stage the solar system is populated by a few thousand planetesimals, such a system is invisible to telescopes
Accretion in a Protoplanetary Disk Star Disk High Density Low Density Larger Grains move to center
Temperature and Phase If the temperature gets too large, the molecules will fly apart Different materials have different melting points Some things are hard to keep solid
Kelvin Scale In astronomy we measure temperature in Kelvin (K) To convert T F = 1.8T K – 460 F and C only tell you relative
Temperature and the Solar Nebula Two basic types of dust in solar nebula: Volatiles -- Refractory Material -- Temperatures were higher in the inner solar system and lower in the outer solar system Inner solar system -- rocky planetesimals Outer solar system -- icy planetesimals
Planetesimals to Planets Due to gravity and intersecting orbits the planetesimals collide with each other Planet formation happens differently in inner and outer solar system
Formation of Gas Giants In the outer solar system you have more material (both volatiles and refractory material), so planets are larger No more hydrogen gas after a few million years Thus, in the outer system where the temperatures are lower you have gas giants
Formation of Terrestrial Planets Result is small rocky planets with no large gassy outer layers
Orbital Evolution This causes: Jupiter, Saturn, Uranus and Neptune are now in different orbits than the ones they were formed in Icy planetesimals ejected to form the Kuiper Belt and Oort cloud
The Final Solar System Our picture of planet formation is driven by an attempt to explain our own solar system and its three regions Outer or Gas Giant region We have also found other types of planetary systems different from our own
Steps in Solar System Formation 1Inner solar system -- volatiles boil off, resulting in small rocky planets 2Outer solar system -- large planet cores form rapidly from refractory and icy material, acquire large gas envelopes 3Edge of solar system -- leftover and ejected icy planetesimals form Kuiper belt and Oort cloud