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Ch.18 - Chemistry of the Environment
All textbooksBrown 15th EditionCh.18 - Chemistry of the EnvironmentProblem 34
Chapter 18, Problem 34

The atmosphere of Mars is 96% CO2, with a pressure of approximately 6 * 10⁻³ atm at the surface. Based on measurements taken over a period of several years by the Rover Environmental Monitoring Station (REMS), the average daytime temperature at the REMS location on Mars is –5.7 °C (22 °F), while the average nighttime temperature is –79 °C (–109 °F). This daily variation in temperature is much larger than what we experience on Earth. What factor plays the largest role in this wide temperature variation, the composition or the density of the atmosphere?

Verified step by step guidance
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Step 1: Understand the composition of Mars' atmosphere. Mars' atmosphere is composed of 96% CO2, which is a greenhouse gas. However, the overall atmospheric pressure is very low, approximately 6 * 10⁻³ atm.
Step 2: Consider the role of greenhouse gases. On Earth, greenhouse gases like CO2 trap heat and help maintain a stable temperature. However, the effectiveness of this process depends on the density and pressure of the atmosphere.
Step 3: Analyze the density of Mars' atmosphere. Despite the high percentage of CO2, the low atmospheric pressure on Mars means there is not enough gas to effectively trap heat, leading to significant temperature fluctuations.
Step 4: Compare with Earth's atmosphere. Earth's atmosphere has a higher pressure and density, allowing greenhouse gases to trap more heat and reduce temperature variations between day and night.
Step 5: Conclude the primary factor. The low density and pressure of Mars' atmosphere play the largest role in the wide temperature variation, as there is insufficient atmospheric mass to retain heat effectively.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Atmospheric Composition

The composition of an atmosphere refers to the types and amounts of gases present. On Mars, the atmosphere is predominantly carbon dioxide (96%), which has different thermal properties compared to Earth's nitrogen-oxygen-rich atmosphere. This composition affects how heat is absorbed and retained, influencing temperature variations. Understanding the role of specific gases in heat retention is crucial for analyzing temperature fluctuations.
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Atmospheric Density

Atmospheric density is the mass of air per unit volume and is influenced by both temperature and pressure. Mars has a much thinner atmosphere (about 0.6% of Earth's), leading to lower density. This reduced density means that there are fewer air molecules to retain heat, resulting in significant temperature drops at night. The relationship between density and temperature variation is essential for understanding Martian climate dynamics.
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Thermal Inertia

Thermal inertia is the ability of a material to conduct and store heat. It determines how quickly a surface can heat up or cool down. On Mars, the low thermal inertia of the thin atmosphere contributes to rapid temperature changes between day and night. This concept is vital for understanding why Mars experiences such extreme temperature variations compared to Earth, where a denser atmosphere moderates temperature changes.
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