The passage of Apophis in April 2029 will be visible to the naked eye. This 27 billion kg asteroid will pass just 32,000 km from Earth, closer than our satellites.
Summary
On April 13, 2029, the asteroid Apophis will pass within 32,000 km (20,000 miles) of Earth, well within the geostationary orbit. With a diameter of 340 m and an estimated mass of 27 billion kg, this is one of the closest passes ever observed for a celestial body of this size. Discovered in 2004, Apophis initially caused concern among astronomers, with some calculations indicating a low probability of impact in the 21st century. New measurements have ruled out this scenario, but the event remains of major importance. Space agencies such as NASA, ESA, and JAXA are preparing observation missions, while astronomers on the ground are refining their models of the dynamics of near-Earth objects. This is a unique opportunity: an asteroid of this size, visible to the naked eye, will provide unprecedented data on its composition, trajectory, and gravitational effects.
An asteroid of extraordinary dimensions
Apophis measures approximately 340 m in diameter and weighs over 27 billion kg. Its trajectory will pass just 32,000 km from Earth, ten times closer than the Moon (384,400 km) and even below the orbit of some geostationary satellites located at 36,000 km. Never before in the modern era has an asteroid of this size been observed passing so close to our planet. This passage therefore provides a unique natural laboratory for studying the gravitational effects of Earth on a massive object. Tidal forces could slightly alter its trajectory and rotation, a phenomenon known as the “Yarkovsky effect” when linked to thermal radiation. Understanding these variations is crucial for improving prediction models for near-Earth asteroids, some of which pose a real risk for the future.
A discovery marked by fear of impact
Apophis was discovered in June 2004 by telescopes at the Kitt Peak National Observatory in the United States. Very quickly, its orbital calculations caused concern among the scientific community: initial estimates suggested a 2.7% probability of impact in 2029, an exceptionally high figure for an object of this size. Additional observations ruled out this scenario, but the question of a future risk remained open. Some models still indicated a possibility of collision in 2068. New radar measurements taken in 2021 by the Goldstone radio telescope have definitively eliminated this hypothesis. Astronomers are now certain that Apophis will not collide with Earth in the next 100 years. Nevertheless, this episode served as a catalyst for strengthening international programs to monitor near-Earth asteroids, known as NEOs (Near-Earth Objects).
A global scientific challenge
The passage of Apophis represents an exceptional scientific opportunity. NASA, through its Planetary Defense Coordination Office, is coordinating monitoring efforts. The Goldstone telescope and large optical observatories such as Pan-STARRS in Hawaii and the future Vera C. Rubin Observatory in Chile will be mobilized. ESA is contributing with its Space Situational Awareness program, which identifies and tracks objects close to Earth. Several agencies are considering sending probes to observe the asteroid up close. The Japanese DESTINY+ mission, initially planned for the asteroid Phaethon, could be adapted. In the United States, studies are exploring the idea of a robotic flyby during the 2029 passage. These projects would collect data on Apophis’ mineralogical composition, density, and rotation, all of which are essential for calibrating future planetary defense scenarios.
The consequences of a hypothetical impact
Although Apophis does not pose an immediate threat, it is legitimate to wonder about the impact of an object of this size. With a diameter of 340 m, it could release energy equivalent to several thousand megatons of TNT in the event of a collision with Earth. By way of comparison, the Chelyabinsk meteorite explosion in 2013 involved an object only 20 m in size, releasing 500 kilotons of energy. The impact of Apophis in a densely populated area on Earth would have catastrophic regional consequences. If it fell into the ocean, it could generate devastating tsunamis. These scenarios justify the scientific and political mobilization around the issue of near-Earth asteroids. They also illustrate the importance of deflection programs, such as NASA’s DART mission, which in 2022 demonstrated the possibility of changing the trajectory of a small asteroid.
A unique opportunity for planetary defense
The Apophis event will provide a full-scale rehearsal to test the responsiveness of scientific and institutional networks. Amateur astronomers and large observatories will participate in data collection. The very close orbit will allow the use of a variety of techniques: high-resolution radar observations, optical spectroscopy, and polarization measurements. These data will not only improve our understanding of Apophis, but also our ability to model other asteroids. At the same time, the event will serve as a full-scale test for international cooperation. Space agencies will have to demonstrate their ability to share information in real time and coordinate their observation campaigns. Ultimately, these exercises are essential in preparing for a possible future crisis involving a truly threatening asteroid.
The cultural and societal impact of Apophis
Beyond science, the passage of Apophis will have cultural significance. Visible to the naked eye in several regions of the world, it will be one of the rare moments when the general public will be able to directly observe a massive asteroid. This event could raise new awareness of cosmic risks and the need to invest in planetary defense. The media will widely cover the event, reinforcing the educational aspect of space research. We must also anticipate irrational reactions: some groups may stir up the idea of an imminent catastrophe, despite scientific assurances. Clear communication from agencies will therefore be crucial in avoiding unfounded fears and turning the event into an educational opportunity.
Towards science applied to global security
The passage of Apophis is part of a broader context: that of managing global risks related to celestial objects. Current programs detect about 90% of asteroids larger than one kilometer, but only half of those larger than 140 meters. However, an object measuring 140 m can already cause a regional catastrophe. Apophis, measuring 340 m, perfectly illustrates the scale of the danger. The 2029 event will serve to refine detection strategies, validate tracking capabilities, and strengthen cooperation between agencies. Investment in these programs remains marginal compared to other military or scientific budgets, but global security issues justify accelerating it.
A long-term perspective
Apophis is symbolic of the relationship between humanity and its cosmic environment. Its passage reminds us that Earth is not isolated, but part of a dynamic system where billions of objects circulate. While the probability of impact remains low, the possibility still exists. As such, the event in 2029 will not only be an astronomical curiosity, but a scientific and political wake-up call. The real question will be whether humanity can turn this opportunity into lasting progress: developing means of deflection, improving early detection, and establishing appropriate international governance. Because even if Apophis does not strike Earth, other asteroids will eventually do so.
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