Explained: How the Chinese landed a rover on Mars in first attempt

China has provided an impressive demonstration of its deep space ca­pabilities by landing a rover on Mars in its first attempt. It is only the second nation after the US to have pulled off a successful Mars landing. The six-wheeled, solar-powered Zhurong rover weighs about 240 kg and its stated technological mission is to collect and analyse rock samples and look for water.

Zhurong was launched from the Tianwen-1 orbiter after three months of preparation. Tianwen reached Mars in February after being launched in July 2020.  It went into orbit around the red planet after the seven-plus-month trip.

Multiple Mars landing missions have failed and a descent to Mars is known to space nerds as the “Seven minutes of terror”. It takes around seven minutes or so for a lander launched from orbit to reach the surface. There are many tricky elements to this, which is why missions by the Russians and the European Union have failed to land a rover in working condition.

Nasa is the only agency that had managed this prior to Zhurong. The lander is completely autonomous and cannot even be monitored in anything approaching real time. At the closest points in their respective orbits, radio signals take 20-odd minutes to cross one-way between Mars and Earth. This means there’s no question of remote-controlling a mission. Second, there’s guesswork involved about the surface of the chosen landing ground. Mars has some regions buried in deep dust and it also has areas with rocky, uneven terrain.

Zhurong had an initial speed of 4.8 km per second (over 17,000 kmph) when it started its descent. It was protected by a heat shield from friction as it entered the thin Martian atmosphere. It released a parachute to slow down, and also used rocket boosters to brake. At about 100 metres above the surface, it hovered and used a laser-guidance system to check for boulders or other hazards in the landing zone.

The orbiter and lander have to calculate the trajectory down, and figure out all the deceleration mano­euvres. The irony is, Mars has eno­ugh of an atmosphere to create serious heat on descent. But it doesn’t have enough atmosphere for parachutes to work very well. Any last-minute course correction is up to the lander if it discovers there’s something gone wrong with the des­cent and landing approach or decides the chosen spot is not suitable.

This rover landed in a region named Utopia Planitia. This is believed to be a lava plain created by volcanic eruptions. On Mars terrain, the landing vehicle will eventually release the rover, which will roll out of the lander, run checks on the equipment and then carry out its mission. The orbiter will act as a data-relay hub that allows Earth mission control to talk to the lander and rover.

The first successful Mars landing was the Viking 1 Mission, which landed in July 1976. The Viking 2 Mission, which followed Viking 1 in short order, landed in Utopia Plan­itia but somewhat North of Zhu­r­o­ng’s chosen spot, in September 1976. Both Viking landers worked for many years but they had far less so­p­histicated instruments, of course.

If all goes well, Zhurong will spend at least 90 Mars days (a Mars day is about 40 minutes longer than an earth day) to study the planet’s geology. Its main task is to look for water ice. Utopia Planitia is believed to contain vast amounts of subsurface water ice.

The Zhurong rover carries an inventory of six instruments for scientific studies. This includes two panoramic cameras, one of which is multispectral and perhaps capable of judging mineral content. It also has ground-penetrating radar and a magnetic field detector as well as a laser and meteorological instrument to study the climate and weather.

Utopia is an impact crater cau­sed by a meteor strike — the largest known impact crater in the Solar System. The Planitia region within the crater may have underground water ice. Zhurong could give us in­sight into several Martian mysteries, besides being an impressive demonstration of Chinese technology.

Climate lessons in Mars

If human beings are ever to use Mars as a colony, we’ll need to answer many questions. If our understanding is correct, millions of years ago, Mars was a warm, wet planet with liquid water and surface oceans, a much thicker atmosphere and a strong magnetic field. It could well have harboured life, given the likely conditions.

Then Mars lost the magnetic field. We don’t know how. Once it lost the magnetic field, it inevitably lost atmosphere. A strong magnetic field protects a planet by blocking solar radiation. Without a shield against solar radiation, the atmosphere is ionised (electrically charged) and gradually stripped away.

Once the atmosphere thinned out, the temperature dropped. The liquid water vapourised, or turned into ice. If we can understand how this happened, we’ll have a better understanding of climate change on Earth and we’ll also have a better idea of whether this process is reversible. Water is also critically important if rockets are going to refuel on Mars and make return journeys.