Question

The atmosphere of Mars is \(96 \% \mathrm{CO}_{2}\), with a pressure of approximately \(0.6 \mathrm{kPa}\) 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 \(-5.7^{\circ} \mathrm{C},\) while the average nighttime temperature is \(-79^{\circ} \mathrm{C}\). 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?

Short answer

The primary factor responsible for the wide temperature variation on Mars is the density of the Martian atmosphere. Although the atmosphere is composed of 96% CO2, which is suitable for trapping heat, its low density (pressure of 0.6 kPa) chiefly diminishes the efficiency of the greenhouse effect, causing significant temperature differences between daytime and nighttime.

Step-by-step solution

Analyzing the role of composition in temperature variation

The composition of the Martian atmosphere is predominantly carbon dioxide (CO2) at 96%. CO2 is a greenhouse gas, which means it can trap heat in the atmosphere. However, because the atmosphere of Mars is much less dense than Earth's, it is less effective at retaining heat during the day, which might explain in part the wide variation in temperature. But we still need to analyze the influence of the density of the atmosphere to make a conclusion.

Analyzing the density of the atmosphere in temperature variation

The pressure of the Martian atmosphere at the surface is approximately 0.6 kPa. Compared to Earth's average surface pressure of approximately 101 kPa, Mars has a remarkably less dense atmosphere. As a result, there are fewer particles in Mars' atmosphere to trap sunlight and heat during the day, leading to more extreme temperature variations.

Comparing the significance of composition and density

On Earth, the greenhouse effect is significant in maintaining relatively stable temperature variations because of its denser atmosphere. On Mars, the composition of the atmosphere, being mainly CO2, would qualify to have a substantial greenhouse effect; however, the low atmospheric density restricts the efficiency of the greenhouse effect.

Conclusion

In conclusion, the primary factor responsible for the wide temperature variation on Mars is the density of the Martian atmosphere. Although the composition is suitable for trapping heat, the low density of the atmosphere largely diminishes the efficacy of the greenhouse effect, leading to significant temperature changes between daytime and nighttime.

Key concepts

Martian Temperature Variation

Mars experiences a remarkable daily temperature variation. During the day, temperatures hover around a chilly \(-5.7^{\circ} \mathrm{C}\), but plummet to a frigid \(-79^{\circ} \mathrm{C}\) at night. This stark difference is much greater than what we see on Earth.
The reason for this lies largely in the characteristics of the Martian atmosphere.
- First, Mars has a very thin atmosphere, with surface pressure being only about \(0.6\, \mathrm{kPa}\), as compared to Earth's \(101 \mathrm{kPa}\).
- With fewer atmospheric particles to hold onto heat, temperatures on Mars can rise and fall dramatically as the planet rotates and sunlight comes and goes.
- This limited capability to retain heat is the main reason behind the large temperature swings Mars experiences daily.
Unlike on Earth, where our denser atmosphere helps moderate such swings, on Mars, the absence of substantial atmospheric density allows the planet to cool rapidly once the sun sets.

Greenhouse Effect on Mars

Mars' atmosphere is composed almost entirely of carbon dioxide, a gas well-known for its heat-trapping abilities. However, Mars does not experience the same stable temperatures as Earth, despite having a high concentration of this greenhouse gas.
This discrepancy is primarily due to the thinness of Mars' atmosphere, which stands at a mere 0.6 kPa compared to Earth's robust 101 kPa. This low density means that Mars struggles to retain steam in the form of warmth.
- While Earth’s dense atmosphere efficiently recycles heat and keeps temperatures relatively stable, Mars has far fewer molecules to trap that heat.
- The result is an ineffective greenhouse effect, which means Mars cannot hold onto solar energy as well as Earth can, making the planet's temperature swing widely between day and night.
Ultimately, while the atmosphere's composition could theoretically support a greenhouse effect, the low atmospheric density severely restricts this potential, leading to less heat retention.

Atmospheric Density on Mars

Mars has a much thinner atmosphere than Earth. The absolute surface pressure is just 0.6 kPa, significantly less than Earth's 101 kPa. This low density is a pivotal factor impacting Mars' climate and temperature variations.
With fewer gas molecules available to absorb and emit infrared radiation, Mars has a limited greenhouse effect.
- This low density means that there isn't enough atmospheric fabric to absorb substantial amounts of solar energy efficiently.
- Consequently, the planet can't keep warmth trapped for long, resulting in the drastic cooling once the sun dips below the horizon.
Where Earth's dense atmosphere acts like a cozy blanket, retaining warmth even during the night, Mars' thin envelope of air is more akin to a sheer scarf, providing minimal warmth retention. Thus, the lower atmospheric density of Mars is the central reason for both its large temperature variability and the limits of the greenhouse effect it can support.