On April 13, 2029, the potentially hazardous asteroid 99942 Apophis will make a breathtakingly close flyby of Earth, providing a once-in-a-lifetime opportunity for more than 2 billion people across Africa and Western Europe to witness this celestial event. Under clear skies, Apophis will appear as a faint star in the night sky, comparable in brightness to the stars in the Big Dipper, and will be easily visible to the naked eye as it glides steadily overhead.
This encounter marks the first time in space history that a potentially hazardous asteroid will be observable without telescopes. Richard Binzel, a professor of planetary sciences at MIT, emphasized the importance of this event during his keynote address at the Europlanet Science Congress in Helsinki, Finland, stating that it offers a rare opportunity to observe how Earth's gravity reshapes a massive asteroid in real-time.
Apophis measures approximately 1,100 feet (340 meters) in diameter, roughly the height of the Eiffel Tower. Astronomers estimate that close approaches by asteroids of this size occur only once every 7,500 years, making this flyby an extraordinary spectacle for the public.
When Apophis was first discovered in 2004, early calculations raised concerns about a potential impact, indicating a 2.7% chance of collision on April 13, 2029, which placed it at Level 4 on the Torino scale. This rating was the highest ever assigned to a near-Earth object. Named after the Egyptian god of chaos, Apophis earned a reputation that caused significant public concern.
However, ongoing tracking and radar observations over the past two decades have significantly reduced the uncertainty surrounding Apophis' orbit. By 2021, the asteroid was officially removed from all risk lists, with scientists concluding that it poses no threat for at least the next century. Although a recent study indicated a tiny possibility of an unknown asteroid nudging it onto a collision path, the odds are over one in a billion, and experts remain confident about Apophis' safe passage.
While Earth will hardly notice this encounter, Apophis will experience changes due to its close approach. It will pass just over 18,600 miles (30,000 kilometers) above Earth's surface—closer than geostationary satellites. This will alter its Aten-class orbit into a wider Apollo-class trajectory and may even affect its rotation, potentially causing it to enter a new tumbling state.
As Binzel explained, "The Earth won’t care, but Apophis will care, because Apophis' orbit will change." To study these changes, NASA has repurposed its OSIRIS-REx spacecraft, now designated as OSIRIS-APEX, to rendezvous with Apophis before the flyby. The spacecraft will map the asteroid's surface, monitor its spin, and measure how Earth’s gravity alters its trajectory.
One of the most exciting goals of the OSIRIS-APEX mission is to measure seismic vibrations within Apophis. According to Binzel, "In 60 years of planetary science, we've only measured seismicity for two objects: the moon and Mars." This presents a unique opportunity to advance our understanding of asteroid interiors and seismic properties.
Additionally, the European Space Agency (ESA) is proposing the Rapid Apophis Mission for Space Safety (RAMSES), which, if approved, would launch in spring 2028 and arrive at the asteroid by February 2029. This mission aims to observe Apophis before, during, and after its flyby, including mapping its orbit and searching for dust clouds raised by tidal forces.
While Apophis itself poses no immediate danger, it serves as a critical proving ground for planetary defense strategies. By studying the effects of Earth's tidal forces on Apophis, scientists can refine models essential for deflecting potentially hazardous asteroids in the future. Tom Statler, a planetary scientist at NASA, explained, "Apophis is not a planetary defense emergency; it is an opportunity—an unprecedented one." He added that asteroids are not something to fear but rather to understand, which is the focus of ongoing scientific efforts.
As we prepare for this monumental event in 2029, the flyby of asteroid 99942 Apophis will not only captivate stargazers but also enhance our understanding of asteroids and their potential impact on Earth.
