▲ At 7:18 on May 15, 2021, the Tianwen-1 landing rover successfully landed on Mars, and the first Mars exploration mission on the mainland landed on Mars successfully. This is the celebration of aerospace researchers in the command hall of the Beijing Aerospace Flight Control Center. Photo: Xinhua News Agency
April 24 is China Space Day.
On the same day, Wu Yanhua, deputy director of the China National Space Administration, said in an exclusive interview with the media that the fourth phase of the lunar exploration project officially started the development of the project this year, and the Chang'e-6, Chang'e-7 and Chang'e-8 probes will be launched successively in the future to carry out mission-critical technology research and the construction of international lunar research stations.
In addition, Wu Yanhua also said that the mainland will begin to form a near-Earth asteroid defense system to jointly deal with the threat of near-Earth asteroid impacts and contribute China's strength to protect the security of the earth and mankind.
So, how did asteroids form, why did they pose a threat to the earth, and how should we detect and understand these asteroids? Answering these questions begins more than 200 years ago.
▲ On December 4, 2020, the China National Space Administration released photos of the lunar exploration project Chang'e-5 probe displayed on the national flag on the lunar surface. Photo: Xinhua News Agency
Meteorfall events are a reminder of asteroid threats
In 1801, it had been almost 200 years since the invention of the telescope. On New Year's Day of that year, the first day of the 19th century, the Italian astronomer Giuseppe Piazzi discovered a new object while observing the starry sky. This was the asteroid 1 that came to be known as Ceres.
It was later learned that around ceres' orbit, there were millions of wandering asteroids, forming a belt of asteroids orbiting the sun, between the orbits of Mars and Jupiter. Some asteroids are disturbed by other celestial bodies, and their orbits change to come to the vicinity of The Earth, called near-Earth asteroids. Among them, the orbit of some asteroids may intersect with the orbit of the earth, posing a threat to the earth, which is the focus of human active defense.
How did these asteroids form? There is a theory in the scientific community that once a planet collided with other celestial bodies, and the resulting debris formed an asteroid belt. Another theory is that asteroids may be the "scraps" left over from the formation of planets and their moons in the solar system, and because they fail to condense into larger planets, they can only float alone in the universe, retaining the original form of the solar system at the beginning of its formation.
It is precisely because these asteroids are of the same origin as the "bricks" that create the "building" of the planets, so the origin and evolution of the solar system can be studied through asteroid detection.
Comets and asteroids are collectively referred to as small bodies. Many of the meteors you see across the night sky on Earth are fragments of comets, but some of them are fragments of asteroids. These extraterrestrial visitors are our first-hand understanding of the solar system, and they are as important as the lunar soil.
Moreover, these asteroids fly very fast relative to the Earth, reaching tens of thousands of kilometers per hour, and once they collide head-on with the Earth, they are extremely destructive. According to theoretical estimates, an asteroid with a diameter of 10 kilometers can cause more than 90% of the earth's organisms to become extinct, and an asteroid with a diameter of about 1 kilometer can also make a super city disappear. In the 1998 Hollywood movie "The Great Collision of Heaven and Earth", this scene was dramatically depicted.
During the Spring Festival of 2013, an asteroid struck a small Russian city of Chelyabinsk, causing a large number of casualties. Later studies found that the asteroid came from the asteroid belt and was only 18 meters in diameter before entering the Earth's atmosphere, and you can see meteorite fragments from the impact at the Beijing Planetarium. In China, there have also been meteorfalls in the Shangri-La, Xishuangbanna and Jilin Songyuan areas in Yunnan, causing social concern.
These real-world events also remind us of the need to be vigilant enough about the potential threat posed by asteroids to Earth.
▲On December 9, 2016, Mozi, China's first quantum science experimental satellite, and the Ali Quantum Teleportation Experimental Platform established a space-earth link (synthetic photo). Photo: Xinhua News Agency
The series of exploration programs is key to understanding asteroids
As a small near-Earth object that combines misfortune and blessing, asteroids are not only important objects for space mining, but also an important goal for the safety of the earth and human beings. Gaining insight into near-Earth asteroids that pose a potential threat to Earth is a prerequisite for building an asteroid defense system.
Some asteroids have abundant resources, such as diamond-rich diamond asteroids. In February 2022, Sotheby's auctioned one of the world's largest naturally cut black diamonds in London, named "Enigma," most likely from space.
With the rapid development of deep space exploration in recent years, the search for diamonds from space has become the target of competition in various countries. Perhaps, the problem of shortage of natural diamond resources on the earth should be answered from deep space exploration.
In addition to meteorite research, the use of spacecraft to detect asteroids is also an important target for deep space exploration. In May 2003, Japan launched the Hayabusa asteroid probe to collect samples from asteroid 25143, Oshima, and returned to Earth in 2010. This is the first time humans have sampled from a near-Earth asteroid that poses a potential threat to Earth.
Since the sample size is only about 1500 particles, it is a challenge for various fine analysis techniques of geochemistry. I also personally observed these black mineral particles from space under the microscope.
In December 2014, Hayabusa's successor, the Hayabusa2 probe, was launched to fly to the Ryugu asteroid about 5.2 billion kilometers from Earth. On December 6, 2020, the Hayabusa2 sample capsule once again brought back more than 5.4 grams of black material from the asteroid. According to the plan, Hayabusa2 is expected to arrive around 2031 with the asteroid numbered 1998KY26 for another exploration.
The United States also attaches great importance to asteroid detection. During the Obama era, an asteroid capture plan was proposed, which proposed to capture a near-Earth asteroid and pull it near the moon to fly around the moon, so that the earth's natural satellite, the moon, also has a satellite. NASA also organized experts to demonstrate this in detail. After Trump took office, he canceled the plan. At present, relevant research in the United States is still underway.
On May 12, 2021, Pluto, another Asteroid probe in the United States, began returning with about 60 grams of samples collected from the Bennu asteroid, and is expected to return to Earth next September.
Europe, for its part, has not only participated in a number of Asteroid exploration programs led by the United States, but has also made breakthroughs in the detection of another small object that may hit the Earth, the comet. In 2004, ESA launched the Rosetta comet probe, and ten years later, in November 2014, the Philae lander landed on comet Chulyumov-Grasimenko, becoming the first spacecraft to land on a comet core expedition.
The implementation of this series of exploration programs is undoubtedly crucial for human beings to understand asteroids and actively respond to their potential threats.
▲ As long as it is properly handled, the near-Earth asteroid belt is also a sea of stars for human beings. The picture shows the asteroid concept. Photo: Xinhua News Agency
Properly addressed asteroids can also benefit human society
According to the results of the preliminary planning and demonstration, the mainland officially announced on the "Space Day" that it will begin to form a near-Earth asteroid defense system. This also means that the continent has accumulated considerable research on near-Earth asteroids.
According to the publicly announced short-term plan, the mainland will strive to carry out an asteroid exploration during the "14th Five-Year Plan" period, and the target of the detection is an asteroid that is potentially threatening to the earth. According to the plan, the spacecraft will approach the probe, perform nearby impacts, and conduct technical tests to change the asteroid's flight trajectory.
Of course, these are only the necessary technical preparations for the formation of a near-Earth asteroid defense system. In order to defend against asteroids hitting Earth, the scientific community still has a lot of work to do.
On the one hand, it is necessary to establish a ground-based and space-based asteroid monitoring and early warning system.
This will require the use of equipment such as ground-based telescopes and lidar, as well as the upcoming launch of the sky survey telescope that accompanies the Chinese space station, to conduct comprehensive monitoring of asteroids that may hit the Earth and pose a potential threat to the Earth. This also includes documenting these asteroids, accurately determining their orbits and characteristics, assessing their likelihood of impacting the Earth, and identifying highly dangerous asteroids early.
On the other hand, it is also necessary to develop new space technologies to ensure the destruction of the original structure of the asteroid or the deflection of its orbit through nuclear explosion, kinetic energy impact, laser ablation, ion beam traction, gravitational drag, mass drive and other technical means, and no longer pose a threat to the earth.
At present, many of the technologies in this series are still only on paper, and there is still a long way to go from the real realization, requiring scientists to carry out computer simulations, carry out experimental verification, and carry out long-term research accumulation to make breakthroughs.
After all, for humans, asteroids are woeful? In fact, as expressed in this year's Hollywood movie "Don't Look Up", whether it is a disaster or a blessing lies in what kind of behavior human beings choose.
If properly dealt with, asteroids will not only not become a threat to the homeland of the earth, but also help us explore the mysteries of space, become the sea of stars for mankind, and even serve as a valuable resource for the benefit of human society. This is undoubtedly the original intention of the continent to form a near-Earth asteroid defense system.
Written by / Long Bridge (Space Exploration and Science Education Expert, Popular Science Writer)
Editor / He Rui
Proofreader / Liu Jun