Let’s go! Towards Mars

Among various deep space explorations, scientists and astronomers have a special liking for the exploration of Mars, the "Earth's closest neighbor". From the first human exploration of Mars in the 1960s to the present, Mars is the planet that has been explored by humans for the longest time, the most times, and with the most participating countries.

For scientists and astronomers, Mars is considered to be another planet besides Earth that may have once bred and supported life. In 1877 , Italian astronomer Schiaparelli even claimed to have discovered "artificial canals" on Mars, pushing the theory of the existence of "Martians" to a climax. Until the 20th century, some people still believed that there was life on Mars.

Deep space exploration was also an important project in the Soviet-American space race in the 1950s and 1960s. Since 1960, the Soviet Union and the United States have successively launched Mars probes, as well as artificial satellites and unmanned space probes to the moon and Venus, and manned spacecraft to low-Earth orbit and the moon. With the end of the space race, people's enthusiasm for Mars has not diminished. Until 27 years ago today, on November 7, 1996, the United States launched the "Mars Global Surveyor" probe with the Delta II carrier rocket , once again opening the prelude to the Mars exploration boom.

Image credit: NASA

The Mars Global Surveyor has a mass of 1,031 kilograms and carries seven instruments. It is part of the U.S. Mars Life Program, and its main mission is to take high-resolution images of the Martian surface, study the Martian topography and gravity field, detect the weather and climate of Mars, and analyze the composition of the Martian surface and atmosphere.

Image credit: NASA

The most exciting observations made by the wide-angle camera system it carries (called the Mars Orbiter Camera) are that the red planet has very regular weather patterns, and weather conditions can occur repeatedly at certain times. At the same time, data sent back by the Mars Global Surveyor show that there is a large amount of dry ice and a small amount of water ice at the poles of Mars, and there may even be liquid water. This indicates the possibility of the existence of life.

It also became the first successful mission to the Red Planet in 20 years. In January 2007, NASA officially announced the termination of the MGS project. After about 10 years of successful operation, MGS also became the longest-lived Mars probe.

What is so difficult about “exploring” a planet spanning billions of kilometers?

The closest distance between Mars and Earth is about 55 million kilometers, and the farthest distance is more than 400 million kilometers. Because Mars is far away from Earth, it is necessary to choose a time when Mars is close to Earth to explore Mars.

Taking into account factors such as risk and cost, the best route for Earth spacecraft to Mars is the "Hohmann orbit" proposed in 1925. Therefore, even if the fastest probe is sent to Mars, it is necessary to wait patiently for the Mars exploration window that occurs every 780 days, or about 26 months, when the Earth and Mars are close. Since this orbit only appears once every 26 months, it has become a time period ("window period") when countries concentrate on exploration. Since 1996, Mars probes have been launched in almost every launch window.

But the process of reaching Mars is too difficult.

First of all, the thin and unstable Martian atmosphere, the Martian surface covered with obstacles such as rocks, slopes, and gullies, the extremely severe Martian dust storms, and the communication delays all pose great risks to landing on Mars.

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Secondly, if you want to go to Mars, you not only need to completely get rid of the Earth's gravity, but also the strong gravitational influence of the sun. This means that more powerful rockets are a prerequisite for exploring Mars.

Third, the probe must be powerful. On the one hand, the cost of Mars exploration is extremely high, and a large number of various scientific instruments must be carried to exchange for the corresponding value. On the other hand, due to the distance problem, the probe's deep space communication, autonomous navigation control, and self-fault detection and repair functions must be independent and powerful, which further pushes up the cost.

Fourth, after the probe reaches the vicinity of Mars, it needs to be captured by the gravity of Mars. Mars capture is one of the most technically risky and critical links in the Mars exploration mission. Compared with the Earth, Mars is just a tiny dot, with a mass of only 10.7% of the Earth, and the range of its gravitational influence is very small, which requires the probe to accurately cut into the orbit around Mars. At the same time, the probe must have a strong ability to change orbits, which can significantly increase fuel demand.

Despite this, countries are stepping up their plans to move toward Mars.

On the long road to Mars, Tianwen-1 makes history

On May 15, 2021, Tianwen-1 landed in the pre-selected landing area in the southern part of Utopia Planitia on Mars, achieving the three major mission objectives of "orbiting, landing, and patrolling" in one mission for the first time. The successful landing of my country's first Mars exploration mission on Mars marks an important step in my country's interstellar exploration journey, achieving a leap from the Earth-Moon system to the interplanetary system, and leaving the Chinese footprint on Mars for the first time.

The first image of Mars taken by Tianwen-1 at a distance of about 2.2 million kilometers from Mars. (Released on February 5, 2021). Image source: China Aerospace Science and Technology Corporation Eighth Academy

As a powerful "space all-rounder", the orbiter played three major roles of spacecraft, communicator and probe in the Tianwen-1 Mars exploration mission, creating many firsts at home and abroad.

One week after landing on Mars, on May 22, 2021, under the careful operation of ground personnel, the Zhurong Mars rover drove off the landing platform; on June 11, the first batch of scientific images of the Tianwen-1 probe landing on Mars were released. China's first Mars exploration mission was a complete success.

Global image of Mars, China's first Mars exploration. Image source: Xinhua News Agency

At present, the orbiter is still "orbiting Mars" and continues to conduct multi-dimensional exploration of Mars. According to the latest news, China's planetary exploration project has approved the implementation of the Tianwen-1, 2, 3, and 4 missions, and plans to implement the "Tianwen-3" exploration mission before 2028, which will complete the first human Mars sample return. This process is more complicated than the "Tianwen-1" mission, and the need for refined Martian atmospheric environmental conditions is more urgent.

Tianwen-1 "landing and patrolling group photo" Photo source: National Space Administration

In the future, will it be possible to "migrate" to Mars?

The harsh environment on Mars does not prevent humans from using their imagination to develop various ideas, and "migrating to Mars" is one of them. So, is it possible for humans to migrate to Mars?

Recently, based on the data obtained by Curiosity during its exploration of Gale Crater, scientists discovered that the criss-crossing cracks in the crater may be filled with water-rich opals, which may be an important resource for future human exploration of Mars. The study also found that the huge underground crack network on Mars provides abundant water and radiation shielding conditions, which may be more suitable for living than the surface of Mars.

Although the vision of transforming it into a green planet suitable for human survival and development is beautiful, it is very difficult to implement: for example, how to transport people and goods to Mars in large quantities; since Mars has no magnetic field and atmospheric protection, the radiation from the sun and cosmic rays is very large, how to solve the radiation problem; there is no oxygen to breathe on Mars, how to produce oxygen or transform the Martian atmosphere; the Martian soil has no organic matter and cannot grow plants, how to transform the Martian soil; the gravity on Mars is only 2/5 of that on Earth, how to solve the problem of human survival in low gravity... But many people are still looking forward to the day when scientists will be able to use more advanced technical means to increase the surface temperature of Mars, increase the concentration of the Martian atmosphere, and further establish the ecological environment on the surface of Mars.

For humans, it is not only a planet, but also represents the exploration of the unknown universe and the future survival and development of mankind. This is why we have a special liking for Mars.

Comprehensive sources: Xinhua News Agency, Liberation Army Daily, Beijing Daily, Science and Technology Herald, etc.