Research efforts locate Tianwen 1 probe on Red Planet

Last month, a set of black-and-white photographs of a desolate desert, showing nothing but rocks, dust and craters, lay in front of Wang Yiran, a postdoctoral fellow at Hong Kong Polytechnic University.

At about the same time, China's Tianwen 1 lander was due to touch down in this desert on Mars. Wang's task was to determine the spacecraft's exact location on a planet about half the size of Earth.

A set of images taken by the lander during its nine-minute touchdown procedure had just been received by the China National Space Administration in Beijing. However, whether the probe had landed successfully had not been confirmed, as scientists and technicians had yet to locate the lander.

It could have been anywhere close to its targeted landing site, which was chosen after input from Wang and her colleagues－a 20-strong team of scientists in Hong Kong led by Wu Bo, a professor in PolyU's department of land surveying and geo-informatics.

The China Academy of Space Technology had set the team the task of analyzing the safest landing site on Mars for the spacecraft.

The location needed to be the flattest area possible, and the team's analysis was vital, as it could make or break the mission. There was no ground control during the landing, as the distance between Earth and Mars means it is impossible to control a spacecraft's descent in real time via radio signals. The landing was described by observers as "nine minutes of terror".

Wu's team stood out during the mission with its innovative topographic mapping and geomorphological analysis techniques as well as its experience. Geomorphology refers to the study of the surfaces of Earth or other celestial bodies.

The team members helped map and evaluate landing sites on the moon for China's Chang'e 4 lander in 2019 and the Chang'e 5 lander last year. The latter mission brought back samples of the lunar surface－the first time this had been achieved for 44 years.

The Tianwen 1 project began in 2016.Comprising an orbiter, a lander and the rover Zhurong－named after the god of fire in Chinese folklore－the mission was launched by a Long March 5 rocket from the Wenchang Space Launch Center in Hainan province on July 23, last year.

On joining the mission, the Hong Kong team was fully prepared for unexpected situations. The mission's field of research was much larger than that for a lunar exploration, and there was also the possibility of communications interference from the Martian atmosphere.

Wang was the only member of the PolyU team to work alongside national astronautic scientists in Beijing for the entire project. Other team members－mainly graduates, doctoral and postdoctoral students－had to remain in Hong Kong due to COVID-19 travel restrictions between the city and the Chinese mainland.

Wang arrived in Beijing soon after the probe began orbiting Mars in February. Scientific findings from the planet, captured by advanced cameras and spectrometers on the Tianwen 1 probe, were transmitted to the Chinese capital.

After receiving the findings, Wang had to send them safely to her colleagues in Hong Kong for analysis. She also represented the team at meetings with national astronautic scientists in Beijing.