Atro Chap. 10-12

• Venus appears very bright, and even a small telescope reveals that it goes through phases like the Moon
• Galileo discovered that Venus displays a full range of phases, and he used this as an argument to show that Venus must circle the Sun and not Earth
• The planet's actual surface is not visible because it is shrouded by dense clouds that reflect about 70% of the sunlight that falls on them, frustrating efforts to study the underlying surface, even with cameras in orbit around the planet
• Mars is more tantalizing as seen through a telescope
• The planet is distinctly red, due (as we now know) to the presence of iron oxides in its soil
• The best resolution obtainable from telescopes on the ground is about 100 kilometers, or about the same as what we can see on the Moon with the unaided eye
• At this resolution, no hint of topographic structure can be detected: no mountains, no valleys, not even impact craters
• Bright polar ice caps can be seen easily, together with dusky surface markings that sometimes change in outline and intensity from season to season
• For a few decades around the turn of the twentieth century, some astronomers believed that they saw evidence of an intelligent civilization on Mars
• The controversy began in 1877, when Italian astronomer Giovanni Schiaparelli announced that he could see long, faint, straight lines on Mars that he called canale, or channels
• At this resolution, no hint of topographic structure can be detected: no mountains, no valleys, not even impact craters. On the other hand, bright polar ice caps can be seen easily, together with dusky surface markings that sometimes change in outline and intensity from season to season.
• For a few decades around the turn of the twentieth century, some astronomers believed that they saw evidence of an intelligent civilization on Mars.
• Canali

  Long, faint, straight lines on Mars that Italian astronomer Giovanni Schiaparelli observed and called "channels"
• The term "canali" was mistakenly translated as "canals" in English-speaking countries, implying an artificial origin.
• Astronomers had watched the bright polar caps change size with the seasons and had seen variations in the dark surface features.
• With a little imagination, it was not difficult to picture the canals as long fields of crops bordering irrigation ditches that brought water from the melting polar ice to the parched deserts of the red planet.
• Percival Lowell


  • A self-made American astronomer and member of the wealthy Lowell family of Boston
  • The most effective proponent of intelligent life on Mars until his death in 1916
• Lowell made what seemed to the public to be a convincing case for intelligent Martians, who had constructed the huge canals to preserve their civilization in the face of a deteriorating climate.
• The Massive Atmosphere of Venus

  • Produces the high surface temperature and pressure on Venus
  • Composed primarily of carbon dioxide
• The thick atmosphere of Venus produces the high surface temperature and pressure on Venus
• When telescopes larger than Lowell's failed to confirm the presence of canals, the skeptics felt vindicated.
• The atmosphere of Venus is composed primarily of carbon dioxide
• The greenhouse effect

  Has led to high temperatures on Venus
• It is generally accepted that the straight lines were an optical illusion, the result of the human mind's tendency to see order in random features that are glimpsed dimly at the limits of the eye's resolution.
• Percival Lowell was born into the well-to-do Massachusetts family about whom John Bossidy made the famous toast: "And this is good old Boston, The home of the bean and the cod, Where the Lowells talk to the Cabots And the Cabots talk only to God."
• Atmosphere of Venus


  Thick, with carbon dioxide as the most abundant gas
• Percival Lowell built an observatory on a high plateau in Flagstaff, Arizona, where he hoped the seeing would be clear enough to show him Mars in unprecedented detail.
• The atmosphere of Venus is very dry, with the absence of water being one of the important ways it differs from Earth
• Atmosphere of Venus


  • Has a huge troposphere (region of convection) that extends up to at least 50 kilometers above the surface
  • Gas is heated from below and circulates slowly, rising near the equator and descending over the poles
• Lowell elaborated his ideas about the inhabitants of the red planet in several books, including "Mars" (1895) and "Mars and Its Canals" (1906), and in hundreds of articles and speeches.
• Cloud layer in Venus' atmosphere

  Composed primarily of sulfuric acid droplets, formed from the chemical combination of sulfur dioxide and water
• Below 30 kilometers, the Venus atmosphere is clear of clouds
• Lowell's views captured the public imagination and inspired many novels and stories, the most famous of which was H. G. Wells' "War of the Worlds" (1897).
• Greenhouse effect


  Causes the high surface temperature of Venus, as the thick CO2 acts as a blanket, making it very difficult for the infrared (heat) radiation from the ground to get back into space
• As the greenhouse effect becomes stronger on Earth

  We are in danger of transforming our own planet into a hellish place like Venus
• Mars is more interesting to most people than Venus because it is more hospitable
• In 1930, Pluto was found at the Lowell Observatory, and it is not a coincidence that the name selected for the new planet starts with Lowell's initials.
• Possible evolution of Venus from an Earthlike climate

  1. Modest additional heating leads to increased evaporation of water from the oceans and the release of gas from surface rocks

  2. This increases atmospheric CO2 and H2O, amplifying the greenhouse effect

  3. Temperature continues to rise in a runaway greenhouse effect
• The rotation period of Mars is 24 hours 37 minutes 23 seconds, just a little longer than the rotation period of Earth.
• Even from the distance of Earth, we can see surface features on Mars and follow the seasonal changes in its polar caps