In the vast cosmos, while the blue planet Earth orbits serenely, it also faces potential threats from the depths of the universe—asteroid impacts. The appearance of asteroid 2024 YR4 is like a stone cast into a calm lake, sending ripples of global concern.

Its every move and future trajectory tug at the heartstrings of all humanity, sparking deep reflection within the scientific community and among the public about Earth's safety and cosmic exploration.

01

Asteroid 2024 YR4: Is Danger Creeping Closer?

On February 19, Beijing time, a message from NASA sent shockwaves around the globe: the probability of asteroid 2024 YR4 impacting Earth on December 22, 2032, had risen to 3.1% (approximately 1 in 32). This figure marks the highest risk assessment for a near-Earth object in nearly 20 years. This asteroid, with a diameter estimated between 40 and 90 meters, has been aptly dubbed a "city killer." Should it strike Earth, it could release energy equivalent to 7.7 to 8 million tons of TNT—enough to devastate a megacity and trigger a cascade of super-disasters like tsunamis and earthquakes.

Data shows that as observational data continues to accumulate, scientists' orbital calculations have become more precise, leading the impact probability to rise gradually from an initial 1.2% to the current 3.1%. This change undoubtedly serves as a wake-up call, forcing us to re-examine the potential crises facing our planet.

History provides sobering reminders of recorded asteroid impact events.

In 1908, the Tunguska event in Siberia, Russia, was caused by the atmospheric explosion of a fragment from an asteroid or comet approximately 50 meters in diameter. The blast flattened about 2,000 square kilometers of forest, demonstrating the immense destructive power of such impacts. More recently, on February 15, 2013, an asteroid about 20 meters in diameter exploded over Chelyabinsk Oblast, Russia, with an energy equivalent to about 500,000 tons of TNT. The event damaged thousands of buildings and injured over 1,500 people.

These real incidents make us acutely aware of the severe threat asteroid impacts pose to human society and heighten our vigilance regarding the potential danger of 2024 YR4.

Although the current impact probability for 2024 YR4 stands at 3.1%, this figure is not static. The European Space Agency's independent assessment places the probability at 2.8%. Scientists generally agree that as observational data continues to be gathered, this value could change—either increasing or decreasing—in the coming months.

Hugh Lewis from the University of Southampton in the UK notes that probability fluctuations are a result of dynamic calculations, and final conclusions still require more data support. This means that while the current probability warrants serious attention, we should not panic based solely on this number but rather continuously monitor subsequent observational and research progress.

02

Tracking Challenges: The Closing Observation Window and Orbital Uncertainties

Tracking asteroid 2024 YR4 presents numerous challenges, a key one being that it is soon to fade from view. Currently, the asteroid is moving away from Earth, and by April 2025, it is expected to become too dim for ground-based telescopes to observe easily, until the next favorable observation window opens around 2028.

During this period, astronomers worldwide are racing against time. On one hand, they are integrating historical data, trying to find more clues about the asteroid's orbit and characteristics. On the other hand, they hope to utilize instruments like the James Webb Space Telescope, which began observations in March 2025, to gather information on its composition and structure, thereby estimating its likelihood of disintegrating in the atmosphere. However, whether there will still be enough time to execute an effective deflection mission when it becomes observable again remains an open question.

Beyond the observation difficulties, the orbital uncertainty of the asteroid poses a significant challenge for threat assessment. 2024 YR4 has an orbital period of about 4 years, with its perihelion inside Earth's orbit and its aphelion outside. This means it crosses Earth's orbit twice each cycle, presenting an impact risk each time, a risk that accumulates over time. This uncertainty makes predicting its future trajectory and impact probability exceptionally difficult for scientists and complicates humanity's efforts to mitigate this threat.

03

Earth's Natural Defenses and Humanity's Technological Shield

(I) The Atmosphere: Earth's Natural "Protective Barrier"

When facing asteroid threats, Earth possesses a natural "protective barrier"—its atmosphere. When an asteroid enters the atmosphere at extremely high speeds, the high temperatures and pressures from the shockwave can cause structurally weak asteroids to break apart into fragments, burning up entirely in this first line of defense.

Throughout history, life on Earth has been spared from many potential asteroid impacts thanks to this atmospheric protection. However, we cannot afford to be complacent. Larger, denser objects can still penetrate this defense and pose a threat to Earth's biosphere.

(II) Global Monitoring: Humanity's Early Warning Network

With technological advancements, humanity has developed the capacity to assess and predict asteroid impact risks. Countries around the world have established asteroid monitoring systems. Using equipment like ground-based optical telescopes, these systems can detect and track hazardous asteroids, providing advance warning of impact timing, location, and potential severity.

For example, the Purple Mountain Observatory of the Chinese Academy of Sciences and the University of Science and Technology of China's "Mozi Survey Telescope" are both engaged in asteroid observation programs. China has also participated in relevant international efforts like the International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG). During the potential impact event of asteroid 2024 XA1 in late 2024, multiple domestic telescopes in China conducted joint observations, contributing to the international response effort.

These monitoring systems and international collaborations provide crucial early warning information for humanity to counter asteroid threats.

(III) Defense Concepts: Altering the Asteroid's Orbit

If an asteroid were confirmed to pose a clear threat to Earth, humanity would not be powerless. Currently, the most viable defense method is to alter the asteroid's orbit by striking it with a spacecraft. In 2022, NASA demonstrated this with its DART mission. The DART spacecraft successfully impacted Dimorphos, the moonlet of the asteroid Didymos, at a speed of 6.6 km per second, shortening its orbital period by 33 minutes and validating the feasibility of this planetary defense method.

China is also actively exploring countermeasures. In 2024, China's Deep Space Exploration Laboratory unveiled concepts for its first near-Earth asteroid defense mission and plans for international cooperation. The mission, planned for around 2030, proposes using an "escort-impact-escort" mode. While an impactor conducts a kinetic impact on the target asteroid, an observer spacecraft will monitor the entire process and subsequently assess the impact's effectiveness and conduct scientific observations.

04

International Action: Building a Unified Global Defense for Earth's Safety

In response to the potential impact risk posed by asteroid 2024 YR4, the United Nations initiated the Planetary Security Protocolfor the first time on February 4, 2025. This move marks a significant step forward in the international community's efforts to address the asteroid threat. It aims to accelerate the construction of a planetary defense system through global cooperation to tackle this worldwide challenge collectively. The activation of the Protocol provides a crucial framework for international collaboration in asteroid monitoring, warning, and defense, facilitating the integration of global resources and coordinated action.

Cooperation among nations is paramount in dealing with asteroid threats. Beyond the UN's coordinating role, astronomers worldwide are actively collaborating, sharing observational data and research findings. For instance, in the observation and study of 2024 YR4, scientists from the United States, Europe, China, and other regions are working together, continuously refining the understanding of the asteroid's orbit and properties through communication and cooperation. Simultaneously, countries are also collaborating on a technical level, jointly developing more advanced monitoring equipment and defense technologies to enhance humanity's capability to address asteroid threats.

Although uncertainty remains regarding the impact probability and future trajectory of 2024 YR4, the international community has reached a consensus: continuous monitoring and technological innovation are key to countering the asteroid threat. Looking ahead, we need to continually improve the global monitoring network, enhance the accuracy and efficiency of asteroid observations, strengthen R&D for defense technologies, and explore more effective mitigation methods. Furthermore, public education is essential to raise awareness and preparedness regarding the asteroid threat. Only through a concerted global effort can we better protect this blue planet and ensure humanity's future safety.

The appearance of asteroid 2024 YR4 has given us a profound understanding of Earth's vulnerability in the cosmos, but it has also showcased humanity's unity and ingenuity when facing cosmic threats. Although the probability of its impact remains uncertain, we cannot afford to be lax. By strengthening global cooperation, sustaining monitoring efforts, and fostering technological innovation, we have the confidence and capability to address this potential threat, safeguarding Earth and humanity's future. In this battle to protect our planet, humanity will continually challenge itself, break through technical bottlenecks, and advance towards a safer and brighter future.