If we allow for a planet with an atmosphere lacking greenhouse gases or dust, the outer boundary of the Sun's habitable zone would be

Question

Quizplus · Accepted Answer

The outer boundary of the Sun's habitable zone is defined as the distance at which a planet would receive less than about 0.2 times the amount of solar radiation that the Earth receives. Without greenhouse gases or dust to trap heat and warm the atmosphere, the habitable zone would be closer to the Sun. Therefore, the best choice is D, just inside the orbit of Mars, which is about 1.5 AU from the Sun.

If We Allow for a Planet with an Atmosphere Lacking