The average temperature of a moon in a steady orbit has been observed to decrease over a long period of time.
Which statement explains why its temperature is decreasing?
The rate of radiation absorbed by the moon is greater than the rate of radiation emitted.
The rate of radiation absorbed by the moon is equal to the rate of radiation emitted.
The rate of radiation absorbed by the moon is less than the rate of radiation emitted.
The rate of radiation emitted by the moon has fallen to zero.