Chapter 3: Nebular Hypothesis Flashcards

Question

What does it mean for a nebula to contract "under it's own self-gravity"

Answer 1

all the particples are attracted together by the cululative gravitational effects of all the other particles in the cloud

Answer 2

**Original Cloud:** * might have been about a light year in diameter. * very low density - perhaps only a few thousand atoms in every cubic centimeter **Solar System Now:** * diameter out to the orbit of pluto is ~17 light minutes * the air around us contains some ten million trillion atoms per cubic centimeter This illustrates the pronounced shrinkage and flattening of the original cloud

Answer 3

Not any Nebula will just collapse under its self-gravity and form a solar system - we see lots of gas clouds that show no indication of doing so There is no evidence for what triggered the collapse of our Nebula. The best explanation is that a pocket of the cloud began to contract because it was recoiling from the shock wave produced from a nearby supernova

Answer 4

1. The best explanation for what triggered the collapse is that a part of the cloud contracted because it was recoiling from the shock wave of a nearby supernova 2. The collapsed region increased in density 3. Atoms were colliding vigorously, generating heat in the process 4. There was a local collapse to that part of the coud 5. This accelerated the collapse 6. Short Lived Increase in temperature from the heat generated by atoms colliding - most heat radiated out into space → temperature is as cool as originally was 7. Eventually, particles so densely packed that heat cannot escape → heat builds up ---- (Any thermal energy (radiation) that is emitted from the hot central regions would be blocked by the surrounding dense layer of matter) ---- particles near the centre are moving at very high speeds (gas is very hot) meaning they can provide enough sustaining pressure to prevent any further collapse 8. Fusion reactions can start to take place → generates even more energy 9. A star is born (our sun) This process happened in less than100,000 years

Answer 5

The sun converts ~600 million tons of hydrogen nuclei into helium nuclei per second, althought this rate is not entirely constant. These are fusion reactions. These fusion reactions convert part of the mass of these atoms (~4 million tons) into energy, and release an enormous amount of heat and light energy into the Solar System Sun loses 4 million tons of mass each second -- the sun will run out of hydrogen fuel in roughly 5 billion years.

Answer 6

It will turn into a red giant and destroy most planets, including earth

Answer 7

1. The Andromeda Galaxy will collide with Milky way in about 3 billion years -- we do not know what this will do to our solar system 2. Our sun will run out of hydrogen fuel in about 5 billion years, will expand into a red giant, destroying most planets including earth

Answer 8

**Momentum:** a measure of an object's tendency to move at a constant speed along a straight path **Angular Momentum:** a measure of the amound of spin (or orbital motion) or an object **Conservation of Angular Momentum:**If no outside force acts on a spinning (or orbiting) object, the object's angular momentum will not change with time, no matter how the objects interacts with other objects.

Answer 9

Some atoms are moving one way, some are moving another way. When all these motions are added up there is likely some slight cumulative motion in some direction -- this defines the angular momentum

Answer 10

* the original cloud likely had some angular momentum * therefore it is inevitable that the cloud will spin faster and faster * with this sense of rotation, as it contracts, it accelerated the spin * just like a figure skater pulling their arms in to spin faster **The inccreasingly rapid spin of orbiting material leads to it's flattening out** **This explains why our solar system is flat, wnad why the planets all originally moved in the same direction as they orbitted the sun**

Answer 11

the flattened nebula had a temperature gradient -- very hot near the center and cooler in the outer regions

Answer 12

The nebula had a homogeneous composition both before and after the collapse and flattening. This means the same mix of chemcials and elements existed throughout. * this means the heavier atoms would NOT have fallen faster towards the protosun than light atoms

Answer 13

The answer is NOT becasue of more water vapour - in general humidity at low altitudes is same as up high. It is becasue of the temperature -- it is cool enough at higher altitudes for water droplets to condense and form large clouds Water vapour goes through the dew point termperature The dew point is the temperature at which air becomes saturated with water vapor and condensation occurs, forming these droplets. When air at a certain altitude cools down to or below its dew point, clouds form at that altitude. the reason for clouds forming at high altitudes is because it is cooler up there, not because there is more water vapour up there (the formation depends on temperature not composition) - similar idea for early solar system -- compositional differences of inner and outer planets were due to temperature gradient.

Answer 14

**At cooler outer regions:** * cool enough that everything condensed (even light elements like hydrogen) **At hotter inner regions:** * only **refractory elements** (those resistant to heat, like metals and silicates) could condense (and freeze) * They condensed to metal oxides, alloys of nicket and iron, etc. * These quickly grew to the size of pebbles * **volatile elements** like hydrogen, water vapour, which boil off at low temperatures, remained completely gaseous in the hot inner regions **This led to compositional diffferences between inner and outer planets** **Inner planets** (Mercury, Venus, Earth, Mars): Formed from heavier elements like metals and silicates. **Outer planets** (Jupiter, Saturn, etc.): Formed from both heavy and light elements, including gases like hydrogen.

Answer 15

Refractory elements (those that do not readily respond to heat) were able to condense and freeze at all temperatures in the gradient. As their atoms and molecules collided, they stuck together and formed strong chemical bonds. The random jiggling and occasional collisions from other particles were not energetic enough to break them apart.

Answer 16

There was no compositional gradient - composition throughout the cloud remained homegenous before and after the collapse and flattening * Therefore, differences in composition of planets were NOT caused by heavier elements being more abundant near the sun The compositional difference in inner vs. outer planets is due to the temperature gradient. * Outer regions were cool enough for everything to condense * inner regions were hot: so ONLY refractory (heavier) elements that were resistant to heat condensed - light elements could not condense and therefore never accumulated into planets

Answer 17

**Accretion:** * describes the process of particles coming together to form larger bodies, first pebbles, then planetesimals, then protoplanets, then planets. **Gravitational attraction** played a key role in accelerating the process of accretion, as larger objects exerted stronger gravitational forces, pulling in smaller objects **Particles → Pebbles:** * Small particles (grains of refractory materials) began to stick together, growing into pebbles. * These pebbles collided gently (due to their shared direction of orbit) and stuck together, gradually forming larger objects, such as stones and boulders. **Pebbles → Planetestimals:** * Over time, these pebbles grew into planetesimals (small planet-like bodies), ranging from 10 to 100 km across - there are still trillions of these **Planetestimals →Protoplanets** Planetesimals continued to collide and merge, growing into protoplanets, which eventually formed the planets we know today.

Answer 18

**The Magic Broom:** Refers to the hypothesis that these extra gases were swept out of the inner solar system toward the end of planet formation * Process not entirely understood therefore given name “magic broom” , which is unfair considering there is strong evidence for it

Answer 19

**Solar Wind**: * The Sun produces a stream of charged particles (mostly electrons) called the solar wind, which flows through the Solar System at several hundred kilometers per second. * **This likely played a role in pushing leftover gases out of the inner Solar System.** **T Tauri Stars**: * These young stars (similar to the Sun when it was forming) exhibit strong winds that could blow away surrounding gas. **Planetary Atmospheres**: * Computer simulations suggest that the atmospheres we see around the rocky inner planets (including Earth) are not the original ones, meaning early atmospheres were likely swept away * New atmospheres for these planets were formed from **outgassing** - particularly, creating a secondary atmosphere from release of volatile substances from volcanoes * The atmosphere of earth has now changed even more with appearance of different life forms etc. For all these reasons, we believe the unused gases n the inner parts of the Solar System were swept out into space.

Answer 20

**Solar Wind:** * a stream of charged particles (plasma - mostly electron) that are ejected from the upper atmosphere of the Sun * this is a continuous phenomenon * flows through the solar system at hundreds of km per second * **Northern lights** are caused by the interaction of solar wind with the Earth's magnetic field

Answer 21

**Solar Flare** a brief eruption of intense high-energy radiation from the sun's surface, associated with **sunspots** and causing **electromagnetic disturbances on the earth, as with radio frequency communications and power line transmissions.** when there is a flare or eruption on the Sun, the **solar wind increases** and the interaction of solar wind with Earth's magnetic field cause** Northern Lights**

Answer 22

computer simulations show that Earths atmosphere is not the original one. This is becasue: * original atmosphere likley swept away by strong solar winds **(magic broom)** * **Outgassing** - the release of volatile substances from volcanoes - likely created a secondary atmosphere * Atmosphere continued to change with the emergence of **diffrent forms of life**

Answer 23

Solar system started as a large, low density cloud of interstellar gas **1. Nebular Collapse:** * possibly caused by shock wave of nearby supernova - no evidence fro what triggered it. * part of cloud contracts, local collapse of part of cloud which accelerates collapse, particles colliding generating heat and energy * eventually, particles so densely packed that heat cannot escape - heat in the hot central regions builds up and is blocked from escaping by the surrounding dense layer of matter * particles near centre are moving fast enough to sustain pressure and prevent further collapse. * fusion reactions can begin to take place * a star is born at the centre (our sun) **Cloud flattening:** * Due to conservation of angular momentum, forming a disk. * there was likely some angular momentum in original cloud when you sum the directions of everything moving * this angular momentum would accelerate as the cloud collapses, which caused it to flatten **Condensation:** * All elements were able to condense in outer regions * Only refractory (heavier) elements were able to condense near the sun, lighter elements remained gaseous **Accretion:** * Small particles stuck together to form pebbles, then planetesimals then protoplanets and full-sized planets. * particles collided gently due to orbiting in the same direction * gravitational force helped with this process, larger objects had stronger grav. force which helped them attract smaller objects. **Magic Broom** * Solar winds and other factors swept out unused gases (those light elements that did not condense) from the inner Solar System into space

Answer 24

* gas was swept into space by solar winds * leftover condensed elements became asteroids (metal/rock) and comets (mostly ice)

Answer 25

**1. Planetary Bombardment**: * in early solar system, there must have been large numbers of planetisimals orbiting and colliding with the growing protoplanets. * Since plantesimals joined protoplanets, the number of planetisimals would have decreased * Therefore, the bombardment rate should have been very high early on and decreased as time passed. * **Bombardment rate:** number of collisions **Evidence:** * the surface of the moon shows a lot of early bombardment that decreased over time **2. Collisions and Their Effects:** The model suggests that there were significant collisions between large bodies late in the formation of the Solar System, which can explain: **Uranus's Tilt:** Uranus is tipped on its side, possibly due to a major collision with another large object. **Venus's Retrograde Rotation:** Venus rotates in the opposite direction to most other planets, likely due to a collision. **Formation of the Moon:** The current theory is that Earth collided with a Mars-sized body, which led to the formation of the Moon. **Mercury’s Orbital Inclination:** Mercury’s orbital inclination varies chaotically, possibly due to past chaotic collisions.

Chapter 3: Nebular Hypothesis Flashcards

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