What is the fine-grained topic of the following text: The $2.5-billion, two-year mission, NASA’s first astrobiology initiative since the 1970s-era Viking probes, kicked off on August 6, with a risky, but successful landing on at a site NASA has named “Bradbury Landing,” a nod to the late science fiction author and space aficionado Ray Bradbury. Only return the topic.
NASA's first astrobiology initiative since the 1970s-era Viking probes