## Astronomy 120: Fall 2008

### Name ___________________________ Section _______

1. A guided question about the mass of planetary atmospheres. This may sound like a tough thing to do, but it really isn't too bad.
1. What is the mass of the Earth's atmosphere? Here's one way to proceed:
• The pressure of the atmosphere at sea level is 1 bar, which is approximately 1 kg / cm2 (this is 14.7 lbs per square inch).
• That means that the mass of the atmosphere above each square cm of the Earth is 1 kg
• The radius of the Earth is 6,330 km. Since the area of a sphere is 4πr2, you can calculate the area of the entire Earth's surface in km2.
• Finally, you know that 1 km2 is 1010cm2, so you can find the total mass of the Earth's atmosphere.

2. Use the same reasoning to find the mass of Mars's atmosphere - you can find the radius of Mars in Table E, and the atmospheric pressure in Chapter 10.

2. On to Venus!
1. Find the mass of Venus's atmosphere as above.

2. You should find that Venus's atmosphere is much more massive than the Earth's. Why do you think this is so (that is, why is the surface pressure so much higher)? A short (5-10 line) answer should be sufficient.

3. From your reading and from lecture, you've learned that Mars is our best hope for finding evidence of life beyond the Earth in our solar system. From what you have learned, and from further investigation, discuss the question of life on Mars in a short (10-15 lines or so) essay. Did Mars ever have any kind of life? If so, did it have simple (bacterial) life only, or perhaps more complex forms? Do you think there is life currently on Mars?