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Origin of the Solar System

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Presentation on theme: "Origin of the Solar System"— Presentation transcript:

1 Origin of the Solar System
Astronomy 311 Professor Lee Carkner Lecture 8

2 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? Bring pencil and calculator!

3 The Solar System The solar system is not just a random collection of planets The solar system has a structure Rocky planets – gas giants – small icy bodies The structure of the solar system is explained by its formation

4 Where Did the Solar System Come From?
Radioisotope dating of the Earth, moon and meteorites indicates that the solar system formed about 4.6 billion years ago 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

5 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 Gravity causes the core to contract to a star Conservation of angular momentum makes the clump spin faster Rapid rotation causes the outer layers to form a disk

6 Star Formation in Action

7 Star Formation in Orion

8 Protoplanetary Disks in Orion

9 Protostellar Jet

10 Circumstellar Disks Disks are fairly cool and can be detected with infrared and millimeter telescopes We also can see them silhouetted against a bright background in Hubble images Disks are common around young stars

11 From Disks to Planets Many stars between 1-50 million years old have disks, but stars slightly older generally do not Where does the disk go? Formed into planets A disk has more surface area than a group of planets with the same mass, so it radiates more light

12 How Do Planets Form? There are 4 stages to planet formation
 dust grains settle to the center of the disk  grains stick together to form planetesimals  planetesimals collide to form planets  gas and leftover planetesimals are cleared from solar system

13 What Was the Solar Nebula Made of?
Solar Nebula -- Initial disk of material that the solar system formed from From studying meteorites and star forming regions we hope to discover what the solar nebula was made of Two basic components Gas -- mostly hydrogen with some helium Dust -- made of silicates (rock) and ices (water, methane, ammonia)

14 Solar System Dust Grain

15 Accretion of Grains Dust grains are very small (< 1 mm), how do they form planets? Grains get larger by sticking together and settle to the center of the disk If dust grains are fractal they may stick together more easily 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

16 Accretion in a Protoplanetary Disk
High Density Star Low Density Larger Grains move to center Accretion in a Protoplanetary Disk

17 Temperature and the Solar Nebula
Two basic types of material in solar nebula: Volatiles -- material with a low boiling point (ices such as water and methane) Refractory Material -- high boiling point (silicates) Temperatures were higher in the inner solar system and lower in the outer solar system Near the Sun the volatiles boiled off leaving only the refractory material behind Inner solar system -- rocky planetesimals Outer solar system -- icy planetesimals

18 Planetesimals to Planets
Due to gravity and intersecting orbits the planetesimals collide with each other The collisions produce larger and larger objects until the planets are formed Planet formation happens differently in inner and outer solar system

19 Formation of Gas Giants
In the outer solar system you have more material (both volatiles and refractory material), so planets are larger Icy planetesimals are “stickier” and form planets faster These large bodies have enough gravity and form fast enough to collect the gas before it all is dissipated Thus, in the outer system where the temperatures are lower you have gas giants

20 Formation of Terrestrial Planets
In the inner solar system planets grew more slowly out of less material, most of it refractory Result is small rocky planets with no large gassy outer layers

21 Accretion of the Inner Planets

22 Beyond the Gas Giants Beyond Neptune the densities are so low and the orbital timescales are so long no planets form at all The left over planetesimals form the Kuiper Belt Other icy planetesimals are ejected by a close encounter with Jupiter or another gas giant Some end up in long orbits with aphelion far from the Sun and form the Oort Cloud

23 Cleaning Up Some of the material in the solar nebula does not end up in the final solar system Some planetesimals are gravitationally ejected from the solar system completely The solar wind will eventually blow most of the unaccreted gas and small particles out of the system

24 The Final Solar System Our picture of planet formation is driven by an attempt to explain our own solar system and its three regions Inner or Terrestrial region Outer or Gas Giant region Trans-Neptunian or Cometary Region We have also found other types of planetary systems different from our own Our picture of planet formation is in a state of flux

25 Icy Rocky Gas Temperature Regions of Formation

26 Summary By looking at stars with protoplanetary disks and the structure of our own solar system and we can develop a theory of how planetary systems form Next step to use data from extrasolar planets Our current picture of planet formation explains the 3 regions of the solar system

27 Summary Inner solar system -- volatiles boil off, resulting in small rocky planets Outer solar system -- large planet cores form rapidly from refractory and icy material, acquire large gas envelopes Edge of solar system -- leftover and ejected icy planetesimals form Kuiper belt and Oort cloud

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