PHYSICS 1040 - ELEMENTARY ASTRONOMY - HOMEWORK #4
1. The terrestrial planets are _______________, _______________, _______________, and _______________. The terrestrial planets are small/large (circle one), more/less dense (circle one), and rocky/gaseous (circle one). They are composed mainly of __________ elements. The orbits of the terrestrial planets are nearly circular and are close to the Sun, so their surface temperatures are __________. The terrestrial planets all orbit the Sun in the same direction and move in the same plane, called the _______________ plane.
2. The Jovian planets are _______________, _______________, _______________, and _______________. The Jovian planets are small/large (circle one), more/less dense (circle one), and rocky/gaseous (circle one). They are composed mainly of __________ elements. The orbits of the Jovian planets are nearly circular and are far from the Sun, so their surface temperatures are __________. Together with the terrestrial planets, the Jovian planets all orbit the Sun in the same direction and move in the ecliptic plane.
3. The speed of a molecule in a gas depends on the _______________ of the gas and the __________ of the gas molecule. Higher gas temperatures mean higher/lower speeds (circle one), while more massive gas molecules mean higher/lower speeds (circle one). Because _______________ is the least massive gas molecule, it will move the fastest. These molecules will thus be the most likely to exceed the _______________ _______________ of a planet, and so escape from the planet's atmosphere. The terrestrial planets are small, hot, and have low escape velocities, so they have almost no _______________. Jupiter and Saturn are large, cold, and have high escape velocities, so they have retained their _______________.
4. Beyond Neptune= s orbit are numerous __________-_______________ objects. The largest of these we know of is __________, while the second-largest is __________. All of these objects orbit the Sun in the same direction as the planets, but their orbit are/are not (circle one) circular and are/are not (circle one) in the ecliptic plane. Astronomers estimate that there are 35,000 of these objects, which are composed mainly of __________ and __________.
5. Impacts of rocky debris have formed _______________ on the planets and their moons. With time, these craters may be removed by the _______________ activity caused by a planet= s or moon= s internal heat. This means that a surface with only a few craters is younger/older (circle one) than a surface with many craters. Also, smaller worlds cool off faster and therefore they have less/more (circle one) internal heat and less/more (circle one) geologic activity, so smaller worlds tend to have fewer/more (circle one) craters.
6. The magnetic field of a rotating planet or moon is caused by its molten interior. The molten material conducts electricity, and the rotating currents produce the magnetic field. This is called the _______________ mechanism. If a planet or moon has a magnetic field, we know that its interior is _______________.
7. Astronomers use _____________ _______________ "fingerprints" to identify the atoms and molecules found in space. They find that the most common element is _______________, which makes up _____ percent of the mass of all the stars and galaxies in the universe. The next most common element is _______________, which makes up _____ percent of the mass. All of the other elements combined make up only _____ percent of the mass of all the stars and galaxies in the universe. Astronomers believe that all of the _______________ and _______________ were made 13.7 billion years ago in the __________ __________, the violent explosion of space at the beginning of time that gave birth to the universe. All other elements were made inside stars, and scattered throughout space by exploding massive stars called _______________. The study of _______________ elements in meteorites shows that our solar system formed 4.56 billion years ago.
8. The law of conservation of _______________ _______________ says that, if the mass of an isolated object doesn't change, then the value of its (size)
2 x (rotation speed) remains constant. This means that if the Sun were to become ten times smaller (with the same mass), then it would rotate ( )2 = _____ times faster. The law of conservation of _______________ _______________ explains why a collapsing interstellar cloud of gas and dust flattens into a disk, called a protoplanetary disk. As the cloud collapses, its size becomes smaller so its rotation rate increases / decreases (circle one). The gas and dust near the cloud= s equator moves fastest and tends to flatten out, just like a ball of spinning pizza dough flattens out. Small clumps of dust then clump together to form _______________ about 1 km across, and these then gravitationally attract each other to form _______________, about the size of our Moon. These then collided to form _______________.9. The early solar nebula contained three types of materials: gases, ices, and rock-forming compounds.
a. _______________ have extremely low condensation temperatures (the temperature at which a gas condenses from a gas into a solid), and so are usually in a gaseous state (unless they are compressed under high pressure into a liquid).
b. _______________ have intermediate condensation temperatures between 100 K and 300 K.
c. _______________ have high condensation temperatures (between 1300 K and 1600 K), and so remain solid at high temperatures.
In the inner solar system, only substances with low/high (circle one) condensation temperatures could have remained solid, so the _______________ planets are small, more dense, and rocky. The _______________ planets were formed where the temperature was cold enough for water to _______________ to form ice.
10. Today astronomers have discovered the presence of more than 270 ______________ (extrasolar planets) orbiting stars other than the Sun. The star and the planet each orbit their common __________ _____ __________, which is their natural balance point. This point is closer to the __________ than it is to the __________. Although astronomers cannot see the planet, they can see the star as it A wobbles@ in a small circle around the __________ _____ __________.