In the reading passage, there is ample evidence as a support for the author's claim that there are plausible theories about why the ashen light of Venus occurs. However, the professor in the lecture gives several reasons as a rebuttal to the author's point.
First, the lecturer contends that it is impossible that the chemical process in Venus can make the ashen light of Venus to occur. The light made by the chemical process in the atmosphere is so faint that people cannot observe the phenomena only with high quality of telescopes. However, the ashen light can be detected by simple telescopes. This casts doubt on the reading passage's claim that the process that carbon monoxide and oxygen are recombined to form carbon dioxide is the reason for this phenomenon.
Next, the lecturer asserts that it is unlikely that the glow is made by light reflection of clouds. The glow of Venus is triggered intermittently. But there is a dense layer of clouds in Venus. If the cloud is the reason for this glow, it must occur constantly. This challenges the reading passage's claim that the sunlight reflected off Venus' a thick layer of cloud is the ashen light.
Finally, the lecturer points out that it cannot be true that aurorae are the reason of the glow. Plasma of sun enter only planets with the magnetic field but Venus does not have the one. For this reason, there is no way that the ashen light is triggered by aurorae. This refutes the reading passage's assertion that plasma from the sun is the cause of light observed on Venus.