Combining orbiting, landing and roving in one mission
Tianwen-1 was the first Mars mission in China's planetary exploration programme, combining an orbiter with a landing assembly carrying a rover. It launched from Wenchang, Hainan, on 23 July 2020, reached Mars in 2021, and subsequently delivered Zhurong to Utopia Planitia.
The mission science plan published by Chunlai Li, Rongqiao Zhang and colleagues grouped its research priorities around habitable environments on Mars and the origin and evolution of Mars and the Solar System. Specific tasks included mapping topography and geological structures, investigating surface soils and indications of subsurface water ice, identifying material composition, and studying the atmosphere, ionosphere, magnetic field and internal structure.
Engineering systems and scientific teams
The planetary exploration initiative launched in 2016 drew on technologies accumulated through China's lunar exploration programme. Five systems supported Tianwen-1: spacecraft, launch vehicle, launch site, tracking and control, and ground applications. The China National Space Administration organized scientific teams to help assess objectives and held exchanges between engineering and scientific communities from 2017 onward. Mission implementation thus involved specialties ranging from instrument development and flight control to data research.
The ground application system comprised its headquarters and receiving stations at Miyun, Wuqing and Kunming. Its responsibilities included science observation planning, payload operations, data reception and processing, interpretation and management, and research applications.
Engineering and research teams also collaborated at different stages. Xiangyu Huang and colleagues at the Beijing Institute of Control Engineering studied entry, descent and landing control, while the Hong Kong Polytechnic University worked with the China Academy of Space Technology on landing-site selection. Subsequent radar papers were jointly produced by researchers at relevant Chinese Academy of Sciences institutes and universities.
From launch at Wenchang to Mars orbit
On 23 July 2020, a Long March 5 launch vehicle sent Tianwen-1 on its journey from Earth to Mars. The mission plan divided the flight into launch, transfer, Mars capture, parking orbit, entry–descent–landing and scientific exploration phases. The spacecraft entered Mars orbit on 10 February 2021 and continued surveying the landing area.
Site selection was constrained by both scientific value and engineering safety. Lower elevations offered more atmospheric deceleration; slopes, boulders and impact craters affected landing risk; and sunlight influenced energy supply and the thermal environment. Using the orbiter's high-resolution camera data, Bo Wu and colleagues closely examined the primary landing area between March and May 2021 and proposed candidate landing ellipses in early May, helping to identify the target in southern Utopia Planitia.
Autonomous descent and Zhurong's departure from the platform
In the early hours of 15 May 2021 Beijing time, the landing assembly separated from the orbiter and entered the Martian atmosphere about three hours later. The long Earth–Mars communications delay required the spacecraft to complete descent autonomously. It first slowed through atmospheric drag, then deployed a parachute, and finally fired its landing engine. Navigation, ranging and obstacle-detection sensors helped the system assess its state and choose a safe location.
The flight-results report by Xiangyu Huang and colleagues records 537 seconds from atmospheric entry to touchdown, with a soft landing at about 07:18 Beijing time. During the final phase, the vehicle hovered at an altitude of about 100 meters to take images and refine its landing-site choice before descending slowly. Zhurong drove off the landing platform on 22 May, beginning surface exploration.
References: [2]
Orbital remote sensing and near-surface exploration
The orbiter carried seven scientific instruments, including medium- and high-resolution cameras, radar, a mineralogical spectrometer, a magnetometer and particle detectors. Zhurong carried six: navigation and terrain cameras, a multispectral camera, a surface-composition detector, ground-penetrating radar, a magnetic-field detector and meteorological instruments. The two payload suites observed Mars at broader scales and at specific sites, respectively.
This combination linked orbital imagery with close-range observations in the rover's exploration area. Cameras recorded landforms and rocks, the composition detector analyzed material properties, and radar supplied clues to subsurface structure. The orbiter also relayed rover data. The original science plan envisaged a 90-Martian-day roving phase, followed by more extensive orbital observations.
References: [1]
Findings and limits of the radar profile
The radar study published by Chao Li and colleagues in 2022 analyzed Zhurong data acquired between 25 May and 6 September 2021 along a traverse of approximately 1,171 meters. Using low-frequency radar, the researchers constructed a subsurface profile extending to about 80 meters in depth. Beneath a surface regolith layer less than 10 meters thick, they identified a multilayered structure about 70 meters thick.
The authors argued that these layers supported multiple episodes of deposition associated with flowing water in Utopia Planitia, while noting that other geological explanations still needed testing. The paper explicitly stated that no direct evidence of present-day liquid water had been found within the radar's detection depth, while subsurface saline ice could not be ruled out.