(1) Saturn is at about 9 AU from the Sun. Earth, of course, is at 1 AU. If distance from the Sun were the only factor controlling the temperature of a planet, Saturn would have a temperature that is: (a) 9 times warmer than the Earth, (b) 9 times colder than the Earth, (c) 3 times warmer than the Earth, (d) 3 times colder than the Earth? Clearly, Saturn has to be colder than Earth. If Temperature is inversely proportional to the SQUARE ROOT of distance, then Saturn will be (9)1/2 = 3 times colder than Earth.
(2) (a) Have you ever gotten into a car that has been sitting out in the sun and sat down on black seats? Did the seat feel hot or cold? Black seats that have been sitting in the Sun are HOT!
(b) Would it have been the same if the seats were white? Nope - the seats would be cooler.
(c) Is it coincidence that people wear white clothing in summer, particularly in hot countries? Obviously not.
(3) (a) Does a dark, black object have an albedo close to 0 or to 1? Zero.
(b) What is the albedo of a white object? The albedo of a white object is close to 1.
(c) Mercury is covered in dark rocks and dust. Do you expect Mercury to have a high (close to 1) or low (close to 0) albedo? Mercury's albedo is close to 0.
(d) If a planet is covered in white clouds do you expect it to have a high (close to 1) or low (close to 0) albedo? A planet covered in white clouds is expected to have a high albedo - close to 1.
(4) Now, consider the effect of albedo on a planet's temperature. (a) If a planet's albedo is small, will a planet be warm or cold? A planet with a low albedo will be dark, will absorb lots of sunlight and be WARM.
(b) If a planet is covered in white frost, would you expect it to be warm or cold? A planet which is white will have a low albedo, reflect sunlight (rather than absorb it) and hence be cold.
(5) (a) The sunlight absorbed by planet is in the visible region of the spectrum. In what region of the spectrum is the light emitted by the planet? Planets emit thermal emission in the infrared region of the spectrum.
(b) The Moon is at a distance of 1 AU from the Sun. The Moon's albedo is very small (about 0.06 - we can approximate this as 0.0). What does this make the equilibrium temperature for the Moon? This is a bit of a trick question. If A = 0.0, the distance is 1 AU from the Sun - then the temperature of the Moon will be just 280K.
(c) See the conversions on Page 121 of the text to convert this to a temperature in Farhenheit. 280K = 7C ~ 45 F.
(6) (a) Fill in the difference between night and day temperatures for each planet. (Subtract the night temperature from the day temperature). Mercury = 600K, Venus =0K , Earth =20K , Mars =63K.
(b) Mercury heats up during its long `day' and cools down at night. How many Earth-days between sunrise and sunset on Mercury? Table C.2 in the Appendic C shows the rotation period of Mercury to be 88 days.
(c) Venus has a high albedo (0.72) - why? Venus is covered in clouds which are good reflectors of sunlight.
(d) For which planet(s), if any, does the equilibrium temperature match the observed temperature? None - Mars comes closest - then Earth.
(7) (a) Using the same technique as in the session on Gravity to fill in the values of the acceleration due to gravity on the surfaces of Mercury and Moon compared with the Earth: You may recall that the gravity on the Moon is about 1/6 that of Earth. Table C.1 shows that the gravity on Mercury is 0.38 that of Earth
(b) WHY is gravity an important factor in determining how much of an atmosphere a planet has? Gravity is important because it holds in the atmospheric gases. When a planet has little gravity, the gases escape and the planet loses its atmosphere.
(8) (a) How many times the Earth sea-level pressure is it on the surface of Venus? The atmospheric pressure at the surface of Venus is 90 times that of Earth.
(b).. and on the surface of Mars? On the surface of Mars the atmospheric pressure is 0.006 times that of Earth.
(c) How high up above the ground on Venus do you have to be before the atmospheric pressure is the same as sea-level on the Earth? The upper diagram shows that when the pressure is 1 bar on Venus, the altitude is 50 km. (50 km is about the top of Earth's atmosphere.)
(9) (a) What are the main constituents of the atmospheres of: (i) EARTH: Nitrogen, with oxygen. (ii) VENUS: Carbon dioxide (iii) MARS: Carbon dioxide
(b) In designing missions for exploration of the terrestrial planets we have to consider what kinds of space suits you need to be comfortable walking on each of the planets.Ê Considering the temperature, pressure and composition of each of the atmospheres of Venus, Mars and Mercury, describe the properties of space suits humans would need to explore these planets. To explore Venus you need a suit that would resist the high gas pressures outside the suit, that would keep you cool, and provide oxygen. For Mars, a suit that would increase the pressure inside and resist the low pressures outside the suit, keep you warm and also provide oxygen to breathe. On Mercury you would need a very robust suit that is pressurized inside and provide oxygen to breathe. Presumably you would want to walk around on the dayside of Mercury so that you could see - then you would need to be kept cool. To explore the night side of Mercury you would need to have a heated suit.
(10) Remind yourself of the "two hump" spectrum of radiation from a planet from Session on Light. In which 2 regions of the electromagnetic spectrum are the 2 humps? The reflected sunlight is in the visible region of the spectrum, the planetary thermal emission is in the infrared region.
(11) (a) Not only does VENUS have more atmosphere then EARTH, but it is nearly all CO2--a green house gas--while Earth's atmosphere is mostly N2 with only a small amount of CO2. Hence, Venus is much hotter than Earth. What is Venus' temperature in Fahrenheit? Venus' surface temperature is 750 Kelvin = 750-273 = 477C = 32 + 1.8 x 477 = 890 F - damn hot!
(b) MARS' atmosphere is mostly CO2. Why is Mars not has hot as Venus? Partly because Mars is farther from the Sun, but mostly because Mars has so little atmosphere - even if it is a greenhouse gas.
(12) (a)What is it about the 4 geological processes that makes it likely that a large planet will have more atmosphere? Atmospheric gases come out of volcanoes. The larger the planet the hotter the interior and the more likely it is to have lots of volcanoes. Hence, the larger the planet, the more atmosphere it is likely to have.
(b) Return to Session 12 where we discussed the 4 geological processes. From just the occurance of volcanism among the 5 terrestrial planets, which would you expect to have substantial atmospheres? Venus, Earth and Mars all have volcanic activity. Only Earth is known to have active volcanism. So, we would expect these 3 planets to have atmospheres, perhaps Earth and Venus more than Mars.
(c) What is it about a planet's gravity that makes it likely that a large planet will have more atmosphere? The larger the planet, the greater the gravity - which allows the planet to hold in atmospheric gases.
(d) Which of the 5 terrestrial planets do you expect to have lost any atmosphere it originally may have had? The smaller ones - Moon and Mercury.
(e) Why is hydrogen particularly easily lost from the terrestrial planets' atmospheres? Because hydrogen is a very light gas - it is easier for it to escape the planet's gravity. (See the bottom of pp 294-5).
(13) (a) On Earth, H2O condensed to form oceans, CO2 dissolved into the ocean (and became carbonate rocks), CO reacted with water to make more CO2--which of the main volcanic gases does this leave to make an atmosphere? Nitrogen.
(b) In which ways has the presence of life on Earth affected the Earth's atmosphere? Flora on Earth have converted CO2 to oxygen.
(14) (a) Comparing the evolution of the atmospheres of Venus and Earth, the critical step is the formation of an ocean--why is the Earth's ocean so important? Carbon dioxide is dissolved in the ocean (it is also probably where life started).
(b) Water not only does not condense on Venus, it is broken up into its constituent elements. What are these elements? Hydrogen and oxygen.
(c) What happens to the hydrogen? The hydrogen escapes, being a light gas.
(d) What does this mean for the possibility of ever having an ocean on Venus, even if the temperature could somehow become cooler? Water is not going to condense out of the atmosphere.
(e) This is sometimes called the "runaway greenhouse effect" - what does "runaway" mean in this case? "Runaway" means that the hotter the planet gets, the greater the greenhouse effect which leads to even higher temperatures.
(15) (a) How is a warmer temperature consistent with more CO2 in the atmosphere? The more carbon dioxide, the greater the greenhouse effect, the higher the temperature.
(b) About 140 thousand years ago there was a large increase in temperature and CO2 concentration. By how many degrees did the temperature increase? By about 10 degrees Celsius. How much did the CO2 concentration increase? From about 190 to 280 units.
(c) These long-term variations are believed to be caused by wobbles in the Earth's orbit and the tilt of the Earth's spin axis. The times of colder temperatures are often called "ice ages" since there were extensive glaciers that spread south from artic regions into the mid-latitudes. From the plot you can see that there are roughly 2 timesscales - one between deep, freezing temperatures (or between very hot spells - this is perhaps easier to measure) and the other, much shorter variations. What are the two timescales for these variations? The longer timescale is about 120,000 years. The shorter timescale is about 10,000 years.
(d) Now, look at the lower plot of modern variations. Note that the temperature scale has now changed to a range of -0.8 C to +0.4 C - about a factor of 10 smaller range that the upper plot. How much is the variation in average, global temperature from year to year? The largest variation from year to year looks about 0.4 degrees.
(e) How much is the variation in temperature, smoothing out the year-to-year variations, over the past 150 years? About 0.5 degrees. Are YOU convinced that there is global warming? Yup - looks pretty real. In fact, at the recent conference about the Kyoto protocol (at which there was not agreement on how to decrease carbon dioxide production), even the Republican representatives agreed that global warming is real.
(f) The red plot is really as much a plot of human activity as a plot of CO2 concentration. What are the ways in which human activity contributes to CO2 production? Powerplants and cars are the 2 main sources of anthropogenic CO2.
(g) What is the prognosis for the future? The top plot shows that the Earth has suffered much larger ranges in CO2 and temperature in the distant past. What would be the impact on present flora and fauna - including humans - of similar ice ages / global warmings? Clearly, the impact could be devastating for life as we know it. On the otherhand, life and humans can adapt to changing conditions. The answer is not clear.
(16) (a) What are the NCAR scientists predicting for the increase in the amount of carbon dioxide over the next (i) 20 years? Only a small amount - about 20% (ii) 300 years? About a factor of 5 (that's 500%) above pre-industrial levels.
(b) What are the predicted changes in temperature (i) in your current location? About 6 C for Boulder.
(ii) maximum on the globe? Maximum is about 8 C.
(iii) minimum on the globe? Minimum is about 2 C.
(c) Described the changes in vegetation that are predicted by the NCAR model. The model suggests major regions of deforestation, particularly on the boundaries - the deserts would expand.
(17) What are the predictions discussed in the article in terms of
(a) flooding - over the next 80 years 200 million people will be affected by flooding.
(b) temperature - land temperatures will go up by about 6C over the next century - about the same as the NCAR predictions.
(c) food production? - drought will cause famine for 30 million people.
(18) Which theory do you think is closer to the truth? I guess it depends on whether you are an optimist or a pessimist!
(19) (a) Why does Mars have so much less atmosphere than Earth? (2 reasons) Less volcanism lead to less atmosphere being generated. Mars' lower gravity meant that it lost more atmosphere.
(b) What factors cause Mars to have fewer volcanoes? Mars is smaller than the Earth so that it cooled off quicker (and had less sources of heat) inside - leading to less volcanism.
(c) What happened to the water on Mars? The water froze in the polar caps and in the regolith ("soil").
(20) (a) Look up the tilt of the spin axes for Earth, Venus and Mars. Earth and Mars have similar tilts (23.5 and 24 degrees) while Venus' tilt is 177 degrees.
(b)Explain why Earth and Mars have seasons, but Venus does not. Mars and Earth will have seasons - the tilt means that the Sun will be shining more directly over one hemisphere at the point in the planet's orbit when that hemisphere is tilted towards the Sun. Venus rotates backwards and very slowly - will essentially no tilt - so there will be no seasons on Venus.
(c) How do seasons on Mars differ from seasons on Earth? Mars' eccentric orbit means that when Mars' southern hemisphere is tilted towards the Sun, the planet is also closest to the Sun. This means that the southern hemisphere summers will be hotter and shorter than the northern hemisphere summers.
(d) Why does atmospheric pressure on Mars change during the seasons, while atmospheric pressure on Earth remains steady year-round? The amount of water frozen in the polar caps decreases (and the amount of water vapor in the atmosphere increases) when the polar cap is in sunlight.