Social media provides science learners opportunities to interact with content-specific messages. However, most science-specific social media content is designed to disseminate information instead of encouraging dialog. In this novel, ex post facto exploratory study of a science social media community, we sought to understand the relationships among community member interaction, design elements of messages, and post type on two digital niches (i.e., Facebook and Twitter). Framed by the theory of symbolic interactionism, we conducted a content analysis of 1370 messages that were systematically created by an informal science learning project and found that usage frequency of messaging elements varied by niche; interaction within each niche differed, varying by messaging element; and differential interaction was found to be associated with post types within Facebook only. This study suggests a pathway for developing and examining social media as an educational component of informal science learning.