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Asteroid Apophis 2029: Closer Than Our Satellites

The asteroid that will pass closer than our satellites

Contents

Asteroid Characteristics Near-Earth Asteroids The 2029 Close Approach The History of an Impact Scare What Scientists Will Learn Kepler's Orbits and the Thinness of Safety
Artist's concept of an asteroid passing close to Earth

NASA/JPL-Caltech

Asteroid Characteristics

Goldstone radar images of asteroid Apophis from March 2021

Goldstone radar images of Apophis, March 2021. NASA/JPL-Caltech

99942 Apophis is a near-Earth asteroid approximately 370 meters (1,210 feet) across — roughly the height of the Empire State Building. Classified as an Aten-group asteroid, it orbits the Sun every 323.6 days at a mean distance of 0.922 AU, spending most of its time inside Earth's orbit. Apophis was discovered on June 19, 2004, by astronomers Roy Tucker, David Tholen, and Fabrizio Bernardi at Kitt Peak National Observatory. It is named after Apep, the ancient Egyptian serpent deity of chaos and darkness — an adversary of the sun god Ra.

Diameter — 370 m (1,210 ft)
Orbital Period — 323.6 days
Mean Distance — 0.922 AU
Group — Aten (NEA)
Discovered — June 19, 2004

Near-Earth Asteroids

Illustration of NEO Surveyor spacecraft scanning for near-Earth asteroids

NASA's NEO Surveyor — the next generation of asteroid hunters. NASA/JPL-Caltech

Near-Earth asteroids (NEAs) are rocky remnants of the solar system's formation whose orbits bring them within 1.3 AU of the Sun. Over 35,000 NEAs have been cataloged to date, ranging from house-sized boulders to objects several kilometers across. Those larger than 140 meters that pass within 0.05 AU of Earth earn the designation Potentially Hazardous Asteroid (PHA) and are actively tracked by planetary defense programs worldwide. They are classified into three orbital families:

Aten — Orbits mostly inside Earth's orbit, crossing it near aphelion.
Apollo — Earth-crossing orbits with semi-major axes larger than Earth's.
Amor — Orbits that approach but do not cross Earth's orbit.

The 2029 Close Approach

Diagram showing Apophis passing closer to Earth than geostationary satellites

Apophis will pass inside the ring of geostationary satellites. NASA/JPL-Caltech

On Friday, April 13, 2029, Apophis will pass within approximately 31,600 km (19,600 miles) of Earth's surface — closer than the geostationary communication satellites orbiting at 35,786 km. For a brief window, the asteroid will be visible to the naked eye, reaching an apparent magnitude of about 3.1, comparable to the star Polaris. Observers in Europe, Africa, and western Asia will have the best views as it crosses the sky like a rapidly moving point of light.

Key Facts

Date
April 13, 2029
Closest Distance
~31,600 km (19,600 mi)
Geostationary Orbit
35,786 km
Peak Brightness
~3.1 mag

The History of an Impact Scare

When Apophis was first tracked in 2004, initial orbit calculations gave it a 2.7% probability of striking Earth in 2029 — the highest impact probability ever recorded for an asteroid. For several tense weeks, the world faced the real possibility of a civilization-threatening impact. Additional observations steadily refined the orbit and eventually ruled out any collision — but the scare revealed both the power and the limits of our planetary surveillance.

2004
Discovered at Kitt Peak. Initial calculations indicate a 2.7% chance of Earth impact in 2029 — the highest ever recorded.
2004–06
Additional observations refine the orbit. The 2029 impact is ruled out. A secondary 2036 impact risk is identified, then also eliminated.
2021
Goldstone radar observations during a distant flyby confirm no impact threat for at least 100 years.
2029
The historic close approach — 31,600 km from Earth's surface, visible to the naked eye.

What Scientists Will Learn

The 2029 flyby is an unprecedented opportunity for planetary science. No asteroid this large has ever been observed at such close range, and the encounter will yield data impossible to obtain any other way.

Radar Mapping — Goldstone and successor facilities will map the surface at meter-scale resolution.
Tidal Effects — Earth's gravity will alter the asteroid's spin rate and may reshape its surface — observable in real time.
Yarkovsky Effect — Measuring the subtle thrust from asymmetric thermal radiation — the dominant uncertainty in long-term orbit predictions.
Planetary Defense — Real-world data to validate deflection strategies for future threatening asteroids.

Kepler's Orbits and the Thinness of Safety

The Nightbase planetarium uses classical Keplerian two-body mechanics to propagate orbits — the elegant ellipses where each body responds only to the Sun's gravity. Under these simplified calculations, Apophis's predicted path results in a collision with Earth on nearly the same date that NASA's models predict the closest real-world encounter.

The difference between catastrophe and a safe flyby comes down to gravitational whispers from distant worlds — subtle nudges that only emerge when you account for every body pulling on every other.

The difference between impact and a safe flyby at 31,600 km comes down to gravitational perturbations from Jupiter, Venus, and the other planets — tiny tugs that accumulate over years and shift the trajectory by just enough. NASA's precise n-body simulations, which account for the pull of every significant mass in the solar system, resolve this hair-thin margin. It is a striking illustration of how delicate the conditions for life on Earth truly are. Our continued existence depends on the combined pull of the major bodies in the solar system. A slightly different Jupiter, a slightly shifted Venus — and the math tips from near-miss to extinction event.

Explore Kepler's Laws of Planetary Motion

Experience the Encounter

Watch the 2029 encounter unfold in real-time 3D. The planetarium jumps to March 2029 and follows Apophis as it sweeps past Earth — closer than our own communication satellites.

Launch Apophis Tour

Sources & Credits

Orbital data: NASA/JPL Center for Near Earth Object Studies (CNEOS). Images: NASA/JPL-Caltech, public domain. Radar observations: Goldstone Deep Space Network, March 2021.