Question at position 34 Does Titan experience a greenhouse effect?No, due to the fact that it is too cold.Yes, due to the presence of methane in its atmosphere.No, due to the absence of carbon dioxide in its atmosphere.Yes, due to the presence of hydrogen in its atmosphere.Yes, due to the presence of nitrogen in its atmosphere.Clear my selection

Question

BlackTom AI · Accepted Answer

Methane is a strong infrared-absorbing gas, so it produces a greenhouse effect on Titan.

1) Relevant knowledge points and concepts
- Greenhouse effect: gases that are transparent to incoming visible sunlight but absorb outgoing thermal infrared radiation trap heat and raise a body's surface temperature.
- Which gases are effective greenhouse gases: molecules with vibrational modes that interact with infrared (e.g., CH4, CO2, H2O). Homonuclear diatomic molecules like N2 and H2 lack a permanent dipole and are poor infrared absorbers.
- Titan’s atmosphere: dominated by nitrogen (N2) with a few percent methane (CH4) plus photochemical hazes. Titan’s surface temperature is measured ≈94 K.

2) Step-by-step reasoning
- Estimate no-atmosphere equilibrium temperature at Titan’s orbit (about 9.5 AU). Solar flux S = 1361 W/m2 / (9.5^2) ≈ 15.1 W/m2.
- Using a Bond albedo A ≈ 0.22 for Titan, the blackbody equilibrium temperature Teq = [S(1−A)/(4σ)]^(1/4).
- Compute S(1−A) = 15.1 × 0.78 ≈ 11.78 W/m2. Divide by 4 → 2.945 W/m2. Divide by σ (5.67×10^−8) → ≈5.19×10^7. Fourth root → Teq ≈ 85 K.
- Observed surface temperature ≈ 94 K, about 9 K warmer than the no-atmosphere estimate. That extra warmth is due to greenhouse trapping of outgoing IR — primarily by methane.

3) Intermediate calculations shown above (flux scaling, albedo factor, division by 4, use of Stefan–Boltzmann constant, fourth-root).

4) Why the correct answer is correct
- Methane has IR-active vibrational modes and even at percent-level abundance can absorb outgoing thermal radiation and produce measurable greenhouse warming on Titan. The observed surface temperature being higher than the blackbody estimate confirms a greenhouse contribution from CH4.

5) Why other options are incorrect
- “Too cold” ignores the measured temperature excess relative to blackbody — Titan is cold but still greenhouse-warmed.
- “Absence of CO2” is irrelevant: CO2 is not required if other IR-active gases (methane) are present.
- “Presence of hydrogen” is incorrect because H2 is a poor IR absorber and is not abundant on Titan.
- “Presence of nitrogen” is incorrect because N2 is homonuclear and does not produce a greenhouse effect (it does provide pressure but not IR absorption).

6) Conclusion
Titan does experience a greenhouse effect, and it is due to the presence of methane in its atmosphere. This matches the provided correct answer: "Yes, due to the presence of methane in its atmosphere."

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