Asteroid Apophis will pass within 32,000 kilometres of Earth’s surface on 13 April 2029, a distance closer than the ring of geostationary satellites that orbit our planet. The flyby, visible to the naked eye across parts of Europe, Africa and Asia, is the closest known approach by an object of this size that scientists have been able to predict in advance. Once feared as a potential impact threat, Apophis now poses no danger, but its arrival offers researchers an unprecedented opportunity. Nasa’s OSIRIS-APEX spacecraft, previously known as OSIRIS-REx, is already on course to reach the asteroid shortly after the encounter, aiming to record how the pull of Earth’s gravity reshapes it.
Asteroid Apophis size, discovery and why it is no longer a threat to Earth
Apophis was discovered in 2004 and briefly considered a possible threat to Earth before further observations ruled out any risk for at least a century. According to Nasa, the asteroid measures roughly 340 metres across, making it a little longer than an American football field and about as tall as the Eiffel Tower. Its 2029 pass will bring it nearer to Earth than many satellites in geosynchronous orbit, an event scientists estimate occurs for an asteroid of this size only once every 7,500 years.The close approach will be visible without a telescope to observers in the Eastern Hemisphere, weather permitting. Ground-based telescopes and radar facilities around the world are expected to track the asteroid intensively in the days before and after the flyby, though Apophis will briefly become impossible to observe from Earth when it passes too close to the Sun in the sky shortly after the encounter.
How Earth’s gravity could reshape asteroid Apophis during its 2029 flyby
The scientific value of the 2029 pass lies in what Earth’s gravitational pull will do to the asteroid as it goes by. The encounter is expected to alter Apophis’s orbit around the Sun, change the length of its roughly 30.6-hour rotation, and potentially trigger small landslides or shifts in surface material, particularly on steep slopes. Researchers will not know the exact effects until they can compare close-up data gathered before and after the flyby. Dani Mendoza DellaGiustina, the mission’s principal investigator at the University of Arizona, said the event amounts to a natural experiment. According to the University of Arizona, she noted that tidal forces and the movement of loose surface material are processes thought to play a role in how planets originally formed, and studying Apophis could help explain how early solar system debris eventually became full-sized planets.
Why NASA redirected the OSIRIS-APEX mission to asteroid Apophis
OSIRIS-APEX began its journey to Bennu under a different name, and after successfully delivering a sample of that asteroid to Earth in September 2023, mission engineers found the spacecraft still had roughly a quarter of its fuel remaining. Rather than retire it, Nasa redirected the craft towards Apophis, renaming it OSIRIS-APEX for Origins, Spectral Interpretation, Resource Identification, and Security, Apophis Explorer. The spacecraft will begin photographing Apophis around 2 April 2029, roughly two weeks before the close approach, as it closes the distance to the asteroid. It will not arrive in Apophis’s immediate vicinity until later that April, after which it will spend around 18 months studying the asteroid using the same suite of cameras, spectrometers and a laser altimeter that mapped Bennu. In a manoeuvre echoing its work at Bennu, the spacecraft plans to descend within about five metres of the surface and fire its thrusters downward to disturb rock and dust, revealing material from beneath.
Why asteroid Apophis is important for studying potentially hazardous asteroids
Apophis belongs to a class of asteroids known as S-types, made of silicate rock and nickel-iron, which differs from the carbon-rich composition of Bennu. Most known potentially hazardous asteroids, meaning those whose orbits bring them within 4.6 million miles of Earth, are also S-types, so findings from Apophis could inform how scientists assess and respond to similar objects in the future.Nasa is not the only agency taking advantage of the encounter. The European Space Agency’s Ramses mission is also being sent to accompany Apophis through its 2029 flyby, adding a second spacecraft to the observation effort. Combined with ground-based telescope and radar campaigns coordinated through Nasa’s International Asteroid Warning Network, the 2029 event is expected to generate one of the most detailed pictures yet of how a close planetary encounter physically alters an asteroid.