China has been busy exploring the inner Solar System in recent years. Their first independent interplanetary mission, Tianwen-1, launched for Mars in 2020. Tianwen-2 is in development, and will launch in 2025 to target a near-Earth asteroid and a main belt comet. Tianwen-3, an ambitious Mars sample return project, is in the planning stages.
Now China’s plans for exploring the outer Solar System are taking shape, with Jupiter’s moon Callisto and one of the ice giants the main targets.
Tianwen-4 at Callisto
The next mission for China, which will be called Tianwen-4, will target Jupiter. As The Planetary Society previously reported, China was considering two main scenarios: the Jupiter Callisto Orbiter, which would focus on said Galilean moon and possibly include a lander, and the Jupiter System Observer, which would study the gas giant’s irregular satellites.
It appears that Callisto will be the prime focus. Zhu Xinbo, deputy chief designer of the Tianwen-1 Mars orbiter and a researcher of China Aerospace Science and Technology Corporation (CASC) — China’s state-owned main space contractor — revealed in a presentation at a joint United Nations/China space exploration workshop, that China’s Tianwen-4 mission to Jupiter looks to be focusing on Callisto. This is backed up by presentations from officials from the China National Space Administration (CNSA).
Zhu’s outline of the mission sees a Tianwen-4 launch in September 2029. The spacecraft will use a flyby of Venus in 2030 plus further gravity assists from Earth in 2031 and 2033, to arrive at Jupiter in December 2035.
At this point, the main spacecraft will enter orbit around the Solar System’s largest planet. But there will also be separation of another probe which will head for Uranus and make a flyby to study the ice giant. According to this launch profile, the spacecraft will zip by the ice giant in March 2045.
The plan to add a Uranus flyby to Tianwen-4 appeared at the International Astronautical Congress in Paris 2022. While brief, it will be an invaluable interaction and only the second-ever visit to Uranus, following Voyager 2’s encounter in 1986.
Back at Jupiter, the main spacecraft will enter orbit around Callisto — the outermost of the four Galilean moons. Before settling in around Callisto it could, though no longer optimized for that particular scenario, make a survey of the irregular satellites. These are thought to be planetesimals captured by Jupiter and are too small to be observed by telescopes. The scope and balance of science objectives is still being discussed by the Chinese planetary science community.