Exploration of extraterrestrial biosignatures and planetary habitability: A prospect

China's deep space exploration has achieved remarkable accomplishments and is now undergoing a significant strategic transition from an engineering-driven program to one that integrates engineering and science. This shift provides a timely opportunity for China to systematically define the development directions and overall framework of planetary science by targeting scientific frontiers, focusing on key research areas, and addressing major scientific questions. In this context, we provide an in-depth analysis of the crucial role of searching for potential biosignatures and investigating planetary habitability for understanding the origin of life. We systematically review the current research state and emerging trends in this field at both the domestic and international levels. Furthermore, we identify three key scientific themes that require urgent attention: planetary habitability, the search for extraterrestrial biosignatures, and the co-evolution of life and habitable environments. For each theme, the major underlying scientific questions are further clarified. Based on these scientific priorities, we also propose key target celestial bodies and critical detection scenarios for future missions. The results are expected to provide important theoretical support for defining scientific objectives and informing the top-level design in China's future planetary exploration endeavors.