In 2029 an asteroid the size of a stadium will pass closer than some satellites

On April 13, 2029, a stadium-sized asteroid named Apophis will pass closer to Earth than the ring of satellites that orbit above the equator, a close approach so certain and so well tracked that astronomers have already planned spacecraft missions around it. The flyby poses no danger to Earth, but its combination of size, proximity, and predictability makes it a rare opportunity to study an asteroid up close without sending a probe deep into the solar system to find one.

A Once-in-a-Generation Close Pass

Apophis, formally designated 99942 Apophis, measures roughly 375 meters across on average, comparable to a large sports stadium, and on its 2029 approach it will come within about 32,000 kilometers of Earth’s surface. According to the European Space Agency’s tracking page for the asteroid, that distance is closer than the roughly 36,000-kilometer altitude where geostationary communications and weather satellites orbit, meaning Apophis will briefly pass beneath that entire ring of spacecraft.

An object of this size passes this close to Earth extremely rarely, and researchers have described the event as the closest approach of an asteroid this large that humans have ever been able to predict in advance. During the flyby, Apophis will be visible to the unaided eye for a period across parts of Europe, Africa, and Asia, a naked-eye view of an asteroid that will otherwise never be bright or close enough to see without a telescope.

A History of Impact Scares That Were Eventually Ruled Out

When Apophis was discovered in June 2004 at Kitt Peak National Observatory, as detailed on NASA’s overview of the asteroid, early orbital calculations put the odds of a 2029 impact as high as 2.7 percent, briefly giving it the highest-ever rating on the Torino scale used to gauge asteroid impact risk. Additional observations over the following years ruled out the 2029 and 2036 passes, though a small chance of impact in 2068 lingered for a while longer.

Radar observations conducted in March 2021 at NASA’s Goldstone Deep Space Communications Complex and the Green Bank Observatory refined the asteroid’s orbit precisely enough for scientists to rule out any impact risk for at least the next hundred years, and Apophis was formally removed from the European Space Agency’s risk list later that month. That history is part of why the 2029 flyby now draws scientific interest rather than public alarm: an object that once represented a genuine, if small, planetary threat is understood well enough today to be treated as a safe, predictable natural experiment.

Studying What Earth’s Gravity Does to an Asteroid

Passing this close to a planet the size of Earth will subject Apophis to measurable tidal stresses, the same kind of gravitational tugging that can trigger landslides, quakes, or subtle shifts in an asteroid’s rotation and internal structure. The encounter is also expected to reshape the asteroid’s path around the sun, shifting it from the Aten group of asteroids, whose orbits sit mostly inside Earth’s, into the Apollo group, whose orbits are wider than Earth’s, and stretching its orbital period from about 0.9 years to about 1.2 years.

Because researchers know the exact date of the encounter years in advance, they have been able to plan detailed before-and-after observations rather than reacting to a surprise event, giving this flyby an unusually well-prepared scientific program compared with most asteroid encounters.

Spacecraft Already Waiting for the Encounter

NASA is repurposing a spacecraft that already has asteroid experience for the occasion. The probe that once carried samples home from asteroid Bennu has been redirected toward Apophis under the renamed OSIRIS-APEX mission, and it is scheduled to rendezvous with Apophis in June 2029, shortly after the flyby, firing its thrusters to kick up surface material and give scientists a look at what lies just beneath the asteroid’s outer layer.

The European Space Agency has pursued a parallel plan called Ramses, aiming to send a spacecraft to accompany Apophis through the flyby itself and observe the encounter as it happens rather than only afterward. Together, the two missions would give scientists observations of the same asteroid before, during, and after its closest approach, a level of coverage rarely possible for any near-Earth object.

Why This Flyby Matters Beyond One Asteroid

Apophis is cataloged in detail, including its discovery history and orbital record, on its own reference page, but its real significance lies in what it can teach planetary defense researchers about a broader category of objects. Thousands of asteroids of comparable size are believed to exist in orbits that cross or approach Earth’s, and most have never been observed at close range.

Learning how one of them responds to a near-miss with a planet, from its rotation to its structural integrity, gives scientists a real-world data point for models used to predict how other asteroids might behave if one were ever found on a genuine collision course. In that sense, the 2029 Apophis flyby functions less as a curiosity and more as a rehearsal for a scenario planetary defense agencies hope never actually happens.

This article was produced with the assistance of AI and reviewed by Morning Overview editors.

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