From a review of the novelization:
I think it would be safe to say that many fans considering the lack of spacesuits or helmets a source of irritation in Alien: Covenant. The novelization has Walter embark onto the surface on his own first, ahead of the crew. He performed some scans and determined that there were no pathogens or anything hazardous to the others on the planet.
This simple section, not there in the movie, served to also explain certain things later on in the novel. For example, when Ledward catches a glimpse of the motes after he disturbs the pods, he recalls what Walter said about there being nothing harmful on the surface of Planet 4. After all “there was nothing on this world to worry him. The pathology scans said so.”