First identified in 2004 as a potential threat to Earth, the near-Earth asteroid Apophis has since become an emblem of how our planet narrowly avoided a cosmic disaster.
Initially, calculations indicated that this asteroid, approximately 340 meters in diameter, had a one-in-37 chance of colliding with Earth in 2029. However, further precise tracking has eliminated that possibility. Despite this, Apophis’s 2029 close encounter remains a unique scientific opportunity, described as “a once-per-millennium natural experiment” by Massachusetts Institute of Technology planetary scientist Richard Binzel during a recent workshop. With uncertainties about the dynamics of a near miss with an asteroid, space agencies worldwide are preparing to learn from this event through various missions.
On April 13, 2029, Apophis will pass within 32,000 kilometers of Earth, flying below the orbit of geostationary satellites. During the inaugural workshop on this encounter in 2020, there were no concrete plans to study Apophis. “It’s astounding,” Binzel said at the third workshop held in June in Padua, Italy. “It looked like nothing was happening…. Now we’re thinking about ‘air traffic control’ for Apophis.”
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There are now three major missions planned to closely observe Apophis—by NASA, the European Space Agency (ESA), and the Japan Aerospace Exploration Agency (JAXA). These missions will work in coordination and might also include a smaller, student-led Chinese CubeSat mission.
JAXA’s spacecraft, DESTINY+, is primarily tasked with flying by the active asteroid Phaethon, the source of the Geminid meteor shower. Originally scheduled for a 2025 launch, DESTINY+ has been rescheduled to launch no earlier than April 2028 due to issues with its original rocket, the Epsilon S, necessitating a switch to the larger H3 flagship rocket. This larger rocket will help it reach Apophis on time. DESTINY+ is expected to make first contact with the asteroid several weeks before its close approach to Earth, flying by at a speed of 1.5 kilometers per second. The data gathered will aid ESA’s Rapid Apophis Mission for Space Safety (Ramses), before DESTINY+ continues to Phaethon.
ESA’s Ramses will share a launch with DESTINY+, thanks to a JAXA-ESA agreement. Due to the tight launch schedule set by DESTINY+’s mission, Ramses scientists began developing the mission without complete funding from ESA, explained Paolo Martino, the project manager, at the June workshop. The Ramses spacecraft, except for its JAXA-provided solar arrays, resembles ESA’s Hera, which is slated to reach Didymos in November. Didymos is the target of NASA’s Double Asteroid Redirection Test (DART) mission conducted in 2022.
Ramses will be outfitted with narrow- and wide-angle cameras, a high-resolution imager, hyperspectral and thermal infrared cameras, a plasma spectrometer, and a laser altimeter. It will get as close as 1 km to Apophis. Additionally, Ramses will deploy two CubeSats named Don Quijote and Farinella. Don Quijote, built in Spain and equipped with a seismometer, will land on Apophis a few days before its closest approach to monitor tidal forces from Earth’s gravity. Naomi Murdoch from the Higher Institute of Aeronautics and Space (ISAE) in Toulouse, France, noted that this could provide valuable insights for planetary defense by helping scientists develop strategies to deflect or destroy hazardous asteroids.
Apophis, like many asteroids, is essentially a pile of rubble, but its internal composition remains a mystery. It could be a loose collection of rocks held together by gravity or contain a large solid core, suggested Joe DeMartini, a postdoctoral researcher at the University of Helsinki, during the Padua workshop. “Earth provides the experiment for us…. All we have to do is put an instrument there,” DeMartini remarked. The other CubeSat, Farinella, will be released after Ramses arrives at Apophis and will use radar to examine the asteroid’s internal structure.
Around this time, a student-led mission from China’s Tsinghua University is set to intercept Apophis. If successful, START (Student-Led Threatening Asteroid Reconnaissance of Tsinghua) will pass within approximately 7 km of Apophis at a speed of about 8.7 km per second. The spacecraft will use imagers to document surface changes as Apophis passes Earth. Approved by the China National Space Administration (CNSA), the mission will launch on a Landspace Zhuque-3 rocket in early 2028. Coordination with other missions is crucial to avoid potential deep-space mishaps, likely managed by a U.N.-affiliated expert group.
As these missions proceed in space, ground-based observations will also occur. Marina Brozovic from NASA’s Jet Propulsion Laboratory is organizing observations with the Goldstone Solar System Radar in California, ensuring they do not interfere with Ramses transmissions.
Apophis will likely appear as a fast-moving light point visible to most people on Earth, according to cartographer Michael Zeiler and astronomer Richard Fienberg at the June workshop. The asteroid will pass over western Asia, Africa, and Europe at night, though clouds might obscure the view for some. Despite such a rare event, this won’t mark the end of interest in Apophis.
The Ramses mission might operate for several months beyond the initial encounter, but NASA’s OSIRIS-APEX mission—an extension of the OSIRIS-REx mission that sampled the asteroid Bennu—will approach Apophis after it passes Earth. Arriving on June 5, 2029, APEX will conduct an 18-month study, including the Spacecraft Thruster Investigation of Regolith (STIR) experiment to mobilize surface materials, offering insights into asteroid weathering and cohesion.
Having been launched a decade ago, the spacecraft has enough fuel for this endeavor, according to Michael Nolan, the deputy principal investigator, during the Padua workshop. However, adapting the spacecraft presents challenges since its cameras were designed for Bennu, a B-type asteroid, whereas Apophis is a brighter S-type, requiring adjustments in photography to prevent overexposure.
The U.N. has designated 2029 as the International Year of Asteroid Awareness and Planetary Defense, providing a unique moment to address the existential risks posed by asteroids. “Apophis will safely pass the Earth,” Binzel reiterated during his remarks at the workshop. Named after the Egyptian deity of chaos, the asteroid will be closely monitored, contributing to scientific knowledge and planetary defense strategies.
