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33 Cards in this Set
- Front
- Back
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What properties of our solar system must a formation theory explain? |
1.Patterns of motion of the large bodies ~ Orbit in same direction and plane 2.Existence of two types of planets ~Terrestrial and Jovian 3.Existence of smaller bodies ~Asteroids and comets 4.Notable exceptions to usual patterns ~Rotation of Uranus, Earth’s moon, etc. |
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What theory best explains the features of our solar system? |
-The nebular theory states that our solar system formed from the gravitational collapse of a giant interstellar gas cloud—the solar nebula ~(Nebula is the Latin word for cloud) -Kant and Laplace proposed the nebular hypothesis over two centuries ago -A large amount of evidence now supports this idea |
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Close Encounter Hypothesis |
-A rival idea proposed that the planets formed from debris torn off the Sun by a close encounter with another star. -That hypothesis could not explain observed motions and types of planets. |
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What properties of our solar system must a formation theory explain? |
-Motions of large bodies -Two types of planets -Asteroids and comets -Notable exceptions like Earth’s moon |
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What theory best explains the features of our solar system? |
Nebular theory states that solar system formed from a large interstellar gas cloud. |
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Galactic Recycling |
Elements that formed planets were made in stars and then recycled through interstellar space |
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Evidence from Other Gas Clouds |
We can see stars forming in other interstellar gas clouds, lending support to the nebular theory |
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Conservation of Angular Momentum |
-Rotation speed of the cloud from which our solar system formed must have increased as the cloud contracted -Rotation of a contracting cloud speeds up for the same reason a skater speeds up as she pulls in her arm |
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Flattening |
-Collisions between particles in the cloud caused it to flatten into a disk -Collisions between gas particles in cloud gradually reduce random motions -Collisions between gas particles also reduce up and down motions -Spinning cloud flattens as it shrinks |
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Disks around Other Stars |
Observations of disks around other stars support the nebular hypothesis |
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Where did the solar system come from? |
-Galactic recycling built the elements from which planets formed. -We can observe stars forming in other gas clouds. |
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What caused the orderly patterns of motion in our solar system? |
-Solar nebula spun faster as it contracted because of conservation of angular momentum -Collisions between gas particles then caused the nebula to flatten into a disk -We have observed such disks around newly forming stars |
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Why are there two types of planets? |
-Only rock and metals condensed inside the frost line -Rock, metals, and ices condensed outside the frost line |
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How did the terrestrial planets form? |
-Rock and metals collected into planetsimals -Planetesimals then accreted into planets |
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How did the jovian planets form? |
-Additional ice particles outside frost line made planets there more massive -Gravity of these massive planets drew in H, He gases |
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What ended the era of planet formation? |
-Solar wind blew away remaining gases - Magnetic fields in early solar wind helped reduce Sun’s rotation rate |
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Asteroids and Comets |
-Leftovers from the accretion process - Rocky asteroids inside frost line -Icy comets outside frost line |
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Heavy Bombardment |
Leftover planetesimals bombarded other objects in the late stages of solar system formation |
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Origin of Earth’s Water |
Water may have come to Earth by way of icy planetesimals |
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Captured Moons |
Unusual moons of some planets may be captured planetesimals |
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Giant Impact |
Giant impact stripped matter from Earth’s crust.Stripped matter began to orbit…then accreted into Moon. |
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Odd Rotation |
Giant impacts might also explain the different rotation axes of some planets |
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How would the solar system be different if the solar nebula had cooled, with a temperature half its actual value? |
Jovian planets would have formed closer to Sun |
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Was our solar system destined to be? |
-Formation of planets in the solar nebula seems inevitable -But details of individual planets could have been different |
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Which of these facts is NOT explained by the nebular theory? |
Number of planets of each type (4 terrestrial and 4 jovian). |
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Where did asteroids and comets come from? |
They are leftover planetesimals, according to the nebular theory |
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How do we explain “exceptions to the rules”? |
Bombardment of newly formed planets by planetesimals may explain the exceptions |
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How do we explain the existence of Earth’s moon? |
Material torn from Earth’s crust by a giant impact formed the Moon |
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Was our solar system destined to be? |
-Formation of planets seems invevitable. -Detailed characteristics could have been different. |
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When did the planets form? |
Radiometric dating tells us that oldest moon rocks are 4.4 billion years oldOldest meteorites are 4.55 billion years oldPlanets probably formed 4.5 billion years ago |
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K-Ar dating |
-The ratio of the amount of 40Ar to that of 40K is directly related to the time elapsed since the rock was cool enough to trap the Ar by the following equation: ~t=t1/2 /ln(2) ln ( (Kf + Arf /0.109) / Kf ) -t is time elapsed -t1/2 is the half life of 40K=1.248×109 yr -Kf is the amount of 40K remaining in the sample -Arf is the amount of 40Ar found in the sample. |
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How does radioactivity reveal an object’s age? |
-Some isotopes decay with a well-known half-life -Comparing the proportions of those isotopes with their decay products tells us age of object |
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When did the planets form? |
Radiometric dating indicates that planets formed 4.5 billion years ago |
