In search of signs of life on Mars with China’s sample return mission Tianwen-3

The aim of China’s Mars sample return mission, known as Tianwen-3, is to collect at least 500 g of samples from Mars and return them to Earth around 2031. Here we summarize the scientific objectives of Tianwen-3 and discuss the concept of the mission, from selecting the payload to curating the sample. The mission aims to provide insights into nine scientific themes centred around the main focus of the search for extant and past life on Mars. These nine themes, together with requirements based on technical capabilities, inform the selection of the payload. We present preliminary studies on a full-chain protocol and the strategy for the selection of the landing site and detection of potential biosignatures in the returned samples. We also propose, in strict accordance with the Committee on Space Research’s Planetary Protection Policy, an integrated plan for sample preservation and analysis. This plan involves the establishment of the Mars Sample Laboratory to conduct a comprehensive examination of the returned Mars samples and safeguard Earth against potential exobiological contamination.