Tutorial_III

Habitable Planets In-Class Tutorial III October 25th, 2023 Group Member Names and Student IDs Name: ........................................... ID: ........................................... Name: ........................................... ID: ........................................... Name: ........................................... ID: ........................................... Name: ........................................... ID: ........................................... Name: ........................................... ID: ........................................... 1 Why is Life abundant on Earth? Over the past few weeks, we discussed how Galileo and Kepler were both aware of the role of the atmosphere in protecting life on Earth. In addition, we talked about Richard Bentley’s concept of habitable zone and the modern definition of habitable zone. Finally, we talked about how the extent and location of the habitable zone around a star depends on the surface temperature of a star. In this tutorial, you will get more familiar with the habitable zone of the solar system and will experience how changing the surface temperature of a star changes the properties of its habitable zone. 1 Consider the table below, listing some properties of Earth, Venus and Mars. 1 Adapted from Prather, Edward E., Erika Offerdahl, and Timothy F. Slater. Life in the Uni- verse: Activites Manual. Addison Wesley, 2003. 1

Table 1: Terrestrial Planets Planet Characteristics Venus Earth Mars Planet Mass ( M ♁ ) 0.8 M ♁ 1 M ♁ 0.1 M ♁ Planet Radius ( R ♁ ) 0.95 R ♁ 1 R ♁ 0.5 R ♁ Distance from the Sun 0.7 AU 1 AU 1.5 AU Average Surface Temperature 456 ◦ C 10 ◦ C -95 ◦ C Atmosphere Thick Medium Very Thin 1. Which of the characteristics listed in the table above most likely have the great- est influence on whether or not life can flourish on Earth but not on Venus and Mars? Explain The presence of liquid water on the surface of a planet appears to be one of the central characteristics distinguishing whether or not a planet can harbour life. This requires that the planet be a distance from the central star where the temperature is neither so low that all the water will freeze nor so hot that all the water will boil. We discussed how the region around a star where the temperature is “just right” for liquid water to exist (in the presence of a thick enough atmosphere) is known as the habitable zone . Note that the thinner the atmosphere, the lower the boiling point of water. Atmospheric pressure plays a role in determining boiling temperature of liquids. Recall that water boils at 100 ◦ C at sea level and as you go up in the mountains, water boils at lower and lower temperatures (water boils at 70 ◦ C on top of mount Everest). The reason is that as you go up a mountain, there is less and less atmosphere on top of your head to exert pressure on the water molecules. Less pressure, means 2