An asteroid located 3.0 astronomical units (AU) from the Sun may be treated as a…
PHYSICS · Multi-part · A Level · Physics · Further mechanics and thermal physics · Further mechanics and thermal physics
Problem
An asteroid located 3.0 astronomical units (AU) from the Sun may be treated as a spherical body whose surface redistributes absorbed energy uniformly over the entire sphere. Ignore any internal heat sources.
Assume the following data are known:
• Solar radiant flux incident on Earth’s orbit (1 AU): 1.36 kW m⁻²
• 1 AU = 1.50 × 10¹¹ m
• The asteroid’s surface absorbs all incident sunlight (albedo ≈ 0).
Answer the questions below.
(1) Calculate the radiant flux from the Sun that reaches the asteroid’s orbital distance.
(2) Determine the asteroid’s equilibrium surface temperature under the stated assumptions. Express your answer in kelvins.
(3) The asteroid rotates very slowly, so heat conduction between its day side and night side is negligible. Estimate the maximum daytime temperature at the sub-solar point (the point directly facing the Sun) if you assume the absorbed energy is re-radiated only from a flat circular area at that point rather than from the whole sphere. State any additional assumptions you make.