Astronomy 301 Ch11 homework answers not given in the text
11-4
The greenhouse effect raises the surface temperatures of both planets, but operates much more strongly on Venus where the atmosphere contains a much higher concentration of greenhouse gases.
11-5
Because the high clouds hide the surface. Microwaves emnitted from the surface were detected and assumed to be black body radiation, allowing the temperature to be calculated.
11-6
Mariner 2 detected microwaves with a wavelength of 1.35 cm which were emitted from the surface of Venus. This wavelength would have been very strongly absorbed by any atmospheric water vapor.
11-7
Because of the greenhouse effect.
11-8
The high sulfur content and the detection of radio wave "static" from lightning both suggest current volcanic activity. Sulfur compounds would not remain in the atmosphere in such large amounts if they weren't being replenished occasionally.
11-10
Venus probably had oceans for a while until the carbon dioxide content of the atmosphere became so high that the greenhouse effect raised the temperature to the point where the oceans evaporated and became water vapor. This caused a runaway greenhouse effect since water vapor is a greenhouse gas, and as the oceans began to evaporate the water vapor added to the atmosphere increased the greenhouse warming. In the upper atmosphere UV light from the Sun broke the water molecules into H and O atoms, and the H atoms escaped due to their low mass which caused them to have high speeds. The oxygen combined chemically with sulfur and with materials on the surface.
11-11
On Earth the carbon dioxide has been dissolved in the oceans, deposited in carbonate rocks under water, and deposited by plants in coal and oil deposits. On Venuse there are no oceans, the high temperatures have bgaked the carbon dioxide out of any carbonate rocks which formed when there were oceans, and there are no plants to sequester carbon dioxide.
11-12
The greenhouse effect on Venus became a runaway greenhouse effect when the oceans were evaporating since the water vapor added to the atmosphere was a powerful greenhouse gas. Once the oceans were all gone and the water vapor was removed from the atmosphere through dissociation by UV light and escape of the hydrogen from the planet, the greenhouse effect stabilized since it was then caused only by the carbon dioxide. Venus has since then emitted exactly as much energy as it absorbs and the temperature remains constant.
11-14
Much flatter with fewer highlands (continents). No signs of plate tectonic features, but does have high shield volcanoes similar to those on Earth and presumably also caused by hot spots.
11-15
No signs of plate tectonic activity such as mountain ranges or volcanic arcs or trenches which occur along plate boundaries on Earth are seen on Venus.
11-16
Water bound in rocks lowers the melting point so the water deficient asthenosphere on Venus may not be fluid enough to flow readily and cause plate motion. Another possibility is that the high surface temperature may soften the lithosphere so that it cannot form rigid tectonic plates.
11-17
Hot spot vulcanism on Venus and on Earth, but no plate motion on VEnus so shield volcanoes grow to be very large on Venus. There is also the possibility that VEnus undergoes global volcanic resurfacing every few hundred million years or so, a situation which does not occur on Earth. None of the volcanic activity which occurs due to plate tectonic activity on Earth occurs on Venus, since there is no plate tctonic activity there.
11-18
The equilibrium resurfacing hypothesis suggests that volcanic eruptions steadily resurface the planet, covering up the older craters. The global catastrophe hypothesis suggests that heat builds up under the thick lithosphere, which acts like an insulating blanket, and every few hundred million years an intense period of volcanic eruptions results and resurfaces the planet.
11-19
Greatest elongation occurs when the line of sight from Earth to Venus makes a right angle with a radius from the Sun to Venus. Venus has a much shorter trip from greatest eastern elongation through inferior conjunction to greatest western elongation than it does form greatest western elongation through superior conjunction to greatest eastern elongation.
11-23
A day on Venus is 116.8 Earth days long, and the synodic period of Venus is 584 Earth days. So from one inferior conjunction to the next is 584 Earth days, during which Venus completes exactly five of its days since 584/116.8 = 5. This means that the same side of Venus always faces Earth at inferior conjunction. Probably this is not a coincidence, but rather an effect of Earth's gravity acting on Venus, but no one really understands this yet.
11-24
answer in text
11-25
answer in text - this radiation is infra red and could easily be measured from Earth telescopically except for the fact that the clouds and atmosphere of Venus absorb all of it.
11-27
The clouds don't interfere if the wavelength is significantly larger than the droplets. Watching the clouds begin to block the radio wves as the wavelength is decreased gives a good measure of the size of the droplets.
11-30
This would be a cold planet, particularly at night. During the day some infra red from the Sun would warm the planet's surface, but the heat would be quickly radiated away at night as infra red easily escaped into space. On Venus visible light heats the atmosphere the surface, and very little infra red can excape so the temperature of the surface stays very high.
11-31
Probably very similar since all of these planets have rock surfaces.
11-33
On Earth the sulfur compounds react with water and eventually fall to the ground in the rain. On Venus there is no rain so the sulfur compounds stay in the atmosphere longer and build up to higher levels.
11-34
On Venus hot spots form single huge shield volcanoes. This shows that there are no moving tectonic plates there.