PHYSICS 1040 - ELEMENTARY ASTRONOMY - HOMEWORK #6
1. Mercury data: Average distance from Sun = __________ A.U.
Orbital period = __________ days
Rotational period = __________ days
Diameter = __________ x Earth=s diameter
Average density = __________ x water=s density
Average temperature (day) = __________
oCAverage temperature (night) = __________
oC
Venus data: Average distance from Sun = __________ A.U.
Orbital period = __________ days
Rotational period = __________ days
Diameter = __________ x Earth=s diameter
Average density = __________ x water=s density
Average temperature = __________ oC (day and night)
Mars data: Average distance from Sun = __________ A.U.
Orbital period = __________ years
Rotational period = __________
Diameter = __________ x Earth=s diameter
Average density = __________ x water=s density
Average temperature = __________ oC(day and night)
2. Mercury=s rotational period is exactly 2/3 of its orbital period, a phenomenon call __________-__________ coupling. As a result, the length of one solar day on Mercury (from noon to noon) is equal to _____ of Mercury=s years! __________ forces are responsible for maintaining this relation between Mercury= s rotational and orbital periods.
3. Like the Moon, Mercury has many impact __________. Long ago a huge impact formed the __________ Basin on Mercury. Seismic waves from this impact traveled through Mercury and were focused on a small region exactly on the opposite side of the planet where today we see a jumbled terrain. With so many craters, Mercury=s surface is very young/old (circle one), so astronomers do not believe that Mercury has much __________ activity, and should not have a molten core. We have found that Mercury has a huge __________ core that reaches 75 percent of the way to the surface. This makes Mercury the most __________-rich planet in the solar system. Mercury has a weak magnetic field, only 1 percent of the strength of Earth= s magnetic field. A small part of Mercury= s iron core must therefore be __________ to generate the observed magnetic field, but not __________ enough to cause geologic activity.
4. Venus= rotation is actually _______________, so it rotates clockwise as seen from above Earth= s north pole. The length of a solar day on Venus (from noon to noon) is 116.8 Earth days. This is roughly __________ of Venus= orbital period, so Venus= year is about _____ Venusian days long. Also, the time between the closest approaches of Venus and Earth is 584 days, exactly _____ Venusian solar days. This means that whenever Venus is closest to Earth, the __________ side of Venus faces Earth.
5. Venus= atmosphere is almost all _______________ _______________ (CO
2): 96.5 percent of its atmospheric molecules are CO2. _______________ (N2) makes up most of the remaining 3.5 percent of the molecules. Venus= upper atmosphere rotates around the planet in just _____ days in a _______________ direction, with winds of 350 km/hr. Near the ground, however, the winds are down to about 5 km/hr. The atmosphere is so massive that the atmospheric surface pressure on Venus is _____ times greater than it is on Earth. This is the same pressure found 1 km below the surface of Earth= s oceans. Venus= clouds contain tiny droplets of _______________ acid! The acid does not drop as rain, however, because it evaporates before it hits the ground. The __________ comes from volcanoes on Venus, some of which may still be active. However, the surface of Venus shows no evidence of _______________ _______________.6. The early atmospheres of Venus and Earth started out with about the same amounts of carbon dioxide (CO
2) and water (H2O). The CO2 came from volcanoes, and much of the water came from impacts with comets. But Venus has almost no water and a carbon dioxide atmosphere, while Earth has vast oceans and little carbon dioxide in its atmosphere.a. What happened to Venus' water? Venus is close enough to the Sun for the Sun's heat to have eventually evaporated any water present on the surface of the young Venus. The sunlight broke up the water molecules in the atmosphere into __________ and __________ atoms. The lighter __________ atoms moved fast enough to escape into space. The heavier __________ atoms combined with other substances in Venus' atmosphere. Thus Venus now has almost no water. Because carbon dioxide is a _______________ gas, Venus has a runaway greenhouse effect that heats its surface by an extra 400
oC.b. What happened to Earth's carbon dioxide? Because Earth is farther from the Sun than Venus, its water did not evaporate, but remained in Earth's oceans. Carbon dioxide dissolves in water, and so the carbon dioxide in the young Earth's atmosphere collected in the __________. This carbon dioxide then became chemically bound into carbonate rocks, such as limestone and marble, that formed in the __________. Thus Earth= s atmosphere now has little carbon dioxide, and a gentle greenhouse effect that keeps Earth= s average temperature above the freezing point of water.
7. The elevation of Mars= northern hemisphere is, on average, about 5 km __________ than Mars= southern hemisphere. Also, Mars= northern lowlands show very many/few (circle one) craters, while Mars= southern highlands show many/few (circle one) craters. This means that the surface of the northern lowlands is relatively young/old (circle one), and that the surface of the southern highlands is relatively young/old (circle one). Mars does not have __________ _______________ (the movement of a planet= s crustal plates), so the absence of craters in the north is not due to __________ __________.
8. Mars has some gigantic surface features. Olympus Mons is the largest _______________ in the solar system, it is the size of the state of Utah and is 24 km high, three times as high as Mount _______________ on Earth. Because __________ __________ is absent on Mars, Olympus Mons sat on a volcanic hot spot for millions of years. Valles Marineris is a _______________ that is 4000 km long (the distance between Los Angeles and New York City), 400 km wide, and 8 km deep. This is a __________ valley, where Mars= crust split along a fault line.
9. Mars changes its appearance over the course of a Martian year. This is caused by Mars= elongated orbit. Mars= seasons are caused by the 25
o tilt of its _______________ axis, similar to the cause of Earth=s seasons. However, Mars is much _______________ to the Sun when it is summer in the southern hemisphere. The Sun warms the soil around the southern ice caps while the ice caps remain very cold. This temperature difference powers strong __________ that produce swirling dust storms. These storms can cover the entire surface of Mars, causing large areas of the planet to change color as the dust storms cover or reveal surface features.10. Although Mars is now very dry, in the past some areas of Mars were covered by __________. Robot rovers on Mars have found evidence of _______________ rocks that can form only in standing water like a lake or shallow sea. Also, photos from spacecraft orbiting Mars have found channels and gullies carved by flowing __________. Today, this water is __________. Some frozen water is found beneath the surface of Mars. Frozen water is also found in Mars= polar __________ __________, which also contain frozen _______________ _______________ (CO
2).