Little is known about how incidental exposure to news, interpersonal discussion, and the diversity of social networks interact in social media environments and for science-related issues. Using a U.S. nationally representative survey, we investigate how these features relate to factual knowledge of gene editing. Incidental exposure to science-related news interacts with interpersonal discussion and network heterogeneity and reveals that the relationship between incidental exposure to news and knowledge is strongest among those who discuss the least. Incidental exposure could alleviate knowledge gaps between the Facebook users who are the most and least involved in interpersonal discussions about science.