Asteroid Apophis: The Perfect Candidate for a Global Impact ?

Near-Earth asteroids: Apophis will pass very close to Earth in 2029 — **Near-Earth Asteroids** in green are non-hazardous, orange ones are slightly hazardous, and red ones require close monitoring. The number of truly dangerous objects increases with observations.
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Scientific summary

Astronoo's article examines the asteroid 99942 Apophis, a near-Earth object 340 meters in diameter that will pass just 31,600 km from Earth on April 13, 2029. This exceptional flyby, well within the geostationary orbit (35,786 km), offers a unique opportunity to study orbital mechanics and planetary defense strategies. The article details Apophis's orbital elements, the gravitational effects of the Earth flyby (notably the "keyhole" phenomenon), and subsequent impact risks, now ruled out for 2036 and 2068. It also presents an estimate of the consequences of a potential impact, including crater size and regional damage. Finally, it highlights the importance of missions like DART and the need for continuous monitoring to anticipate potential future threats.

Will Apophis hit Earth ? How long are we safe ?

This article is dedicated to asteroid 99942 Apophis, a 340-meter-diameter near-Earth object that has caused great concern since its discovery in 2004. But will Apophis actually hit Earth? The short answer is no, at least for the 21st century. On April 13, 2029, Apophis will pass just 31,600 km from Earth's surface — much closer than our geostationary satellites — but astronomers have ruled out any collision for that date. Yet the question "How long are we safe?" remains open. The 2029 flyby will profoundly alter Apophis's orbit, and a phenomenon called the "gravitational keyhole" could, in theory, steer the asteroid toward a later impact, perhaps in 2036, 2068, or beyond. Thanks to radar observations from Goldstone and Arecibo, these risks have been reduced to less than 1 in 150,000. But uncertainties remain, notably the Yarkovsky effect — a tiny but cumulative thermal force over the long term — and gravitational perturbations from other bodies in the Solar System. The article explores these scenarios, detailing the orbital elements, the consequences of an impact (4 to 5 km crater, 1000 Mt energy) and deflection technologies like the DART mission. Apophis is not an immediate threat, but a celestial warning that reminds us of our planet's vulnerability.

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A terrifying flyby at 31,600 km

Asteroid 99942 Apophis, discovered in 2004, quickly attracted the attention of astronomers worldwide. In 2029, it will pass just 31,600 km from Earth's surface, well within the geostationary satellite orbit (35,786 km). At this distance, Apophis will be visible to the naked eye from certain regions of the globe.

The 31,600 km flyby: a high-precision estimate

This flyby, the closest ever observed for an object of this size (340 meters in diameter), represents a unique case study for orbital mechanics and planetary defense strategies. The passage of asteroid Apophis at a distance of approximately 31,600 km from Earth on April 13, 2029 is the result of precise measurements, complex orbital modeling, and advanced celestial mechanics techniques.

The 31,600 km perigee is measured from Earth's center. This places Apophis within the geostationary orbit (35,786 km), but well above the atmosphere. Its trajectory will not cross any known major satellites (operators and agencies have checked for collision risks).

Zero impact risk for 2029, but the "keyhole" exists

Thanks to precise radar observations from Goldstone and Arecibo, NASA has ruled out any collision risk with Earth for 2029. However, Apophis's trajectory will be significantly altered by Earth's gravitational effect — a phenomenon called the "gravitational keyhole". If the asteroid passes through a narrow region of space (about 600 meters wide), its trajectory could be deflected in a way that leads to an impact on a later return, notably in 2036 or 2068.

Current calculations, based on N-body dynamics and gravitational perturbations, show that the impact risk for these dates is less than 1 in 150,000. But orbital uncertainties, the Yarkovsky effect (long-term thermal perturbation), and future interactions with other Solar System objects require constant monitoring.

Table of approximate orbital elements of Apophis (2024–2026)

Orbital elements of Apophis (2024-2026)
Orbital element	Value (2024)	Value (2025)	Value (2026)
Semi-major axis (a)	0.92255214 AU	0.92255214 AU	0.92255214 AU
Eccentricity (e)	0.19129073	0.19129073	0.19129073
Inclination (i)	3.33973639°	3.33973639°	3.33973639°
Perihelion (q)	0.74607647 AU	0.74607647 AU	0.74607647 AU
Aphelion (Q)	1.09902781 AU	1.09902781 AU	1.09902781 AU
Orbital period (P)	0.8861 yr (≈ 323.66 d)	0.8861 yr (≈ 323.66 d)	0.8861 yr (≈ 323.66 d)
Argument of perihelion (ω)	126.6832°	126.7005°	126.7178°
Longitude of ascending node (Ω)	203.96°	204.12°	204.28°
Mean anomaly (M)	195.65°	75.42°	198.30°
Next perihelion date	February 12, 2025	January 25, 2026	January 7, 2027

N.B.:
These values are approximations and may vary slightly depending on models and observational corrections.

Apophis: A Natural Laboratory for Deflection Technologies

The threat posed by Apophis has stimulated research into asteroid deflection technologies. Missions like DART (NASA, 2022) have demonstrated the feasibility of altering a body's trajectory through kinetic impact. Apophis offers an in-situ test opportunity: several agencies are considering sending probes to study its internal structure, density (estimated at \( 3\, \text{g/cm}^3 \)) and silicate composition.

An Apophis impact would release kinetic energy equivalent to more than \( 1000\, \text{Mt} \) of TNT, about 80,000 times the energy of the Hiroshima bomb. With its 340-meter diameter, estimated density of \( 3\, \text{g/cm}^3 \) and typical impact velocity of \( \sim 12\, \text{km/s} \), Apophis would pass through Earth's atmosphere without completely disintegrating. It would strike the ground, forming a crater several kilometers in diameter and causing major regional or even continental damage, depending on the impact zone.

Realistic crater estimate for Apophis (340 m, 12 km/s)

Final crater diameter: 4 to 5 km
Crater depth: 500 to 800 m
Destructive shock wave: up to 100–200 km around the impact point
Thermal effects / blast: destructive up to hundreds of kilometers depending on geography.

A celestial warning

The April 13, 2029 flyby

Apophis will not hit Earth in 2029, 2036 or 2068, but it brutally reminds us that our planet is not safe from a cataclysmic event from the sky. The most critical approach is that of April 13, 2029, but no collision is predicted in the 21st century.

The imperative of monitoring and deflection

Precise tracking of near-Earth objects, detailed understanding of their orbits, and the development of deflection technologies are becoming a scientific and strategic imperative. The question scientists must answer is "When could such an impact occur?"

Future dates of Apophis passages near Earth
Year	Distance (km)	Impact risk	Remark
2029	31,600	0 %	Historic flyby, visible to the naked eye from Europe, Africa and Asia. Unprecedented study for planetary defense.
2036	~14,000,000	0 %	Risk definitively ruled out in 2013 thanks to Goldstone and Arecibo radar observations.
2068	~38,000,000	0 %	More than 100 lunar diameters away. No risk identified.
2116	~200,000 (possible)	<\(10^{-6}\)	Orbital resonance scenario still under study. Uncertainties linked to Yarkovsky effect and planetary perturbations.
2126	~4,000,000	~ \(10^{-8}\)	Passage with no major risk according to current celestial mechanics models.
2136	~50,000	<\(10^{-5}\)	Very close passage, but impact probability infinitesimal. Requires continuous monitoring.

N.B.:
Beyond 2116, orbital predictions become highly uncertain due to the chaotic dynamics of the Solar System, the Yarkovsky effect (cumulative thermal perturbation) and gravitational interactions with other celestial bodies. The distances and risks indicated are estimates based on current models and are subject to revision with new observations.

References

FAQ: Everything you need to know about asteroid Apophis

What is asteroid Apophis?

Apophis (99942) is a near-Earth asteroid 340 meters in diameter, discovered in 2004. It is classified as a potentially hazardous object due to its orbit crossing Earth's.

When will Apophis pass near Earth?

The closest pass will occur on April 13, 2029, at a distance of only 31,600 km from Earth's surface. It will be visible to the naked eye from some regions of the world.

Will Apophis hit Earth in 2029?

No. Astronomers have ruled out any collision with Earth for 2029 thanks to precise radar observations.

What is the "gravitational keyhole" phenomenon?

It is a narrow region of space (about 600 meters) where Apophis's passage in 2029 could alter its future trajectory, directing it toward a later impact, for example in 2036 or 2068. The risks for these dates are less than 1 in 150,000.

What are the consequences of an Apophis impact?

An impact would release energy of over 1,000 megatons of TNT, creating a 4 to 5 km diameter crater and causing major regional or even continental damage, depending on the impact zone.

What is the Yarkovsky effect?

The Yarkovsky effect is a thermal perturbation that modifies an asteroid's orbit over the long term. It is caused by the asymmetric emission of infrared radiation from the asteroid's heated surface, acting as an additional force.

Are there technologies to deflect an asteroid like Apophis?

Yes. The DART mission (NASA) demonstrated in 2022 the feasibility of deflection by kinetic impact. Other techniques, such as using a gravitational tractor or surface nuclear explosion, are also being studied.

What should be done if an asteroid threatens Earth?

Space agencies like NASA and ESA continuously monitor near-Earth objects. In case of a confirmed threat, deflection scenarios are prepared, ranging from kinetic impact to nuclear charges, depending on size and available lead time.

Why is Apophis nicknamed the "God of Chaos"?

Apophis is named after the Egyptian god of chaos, Apep (or Apophis), due to the threat it initially posed. This name reflects the unpredictable and potentially dangerous nature of near-Earth asteroids.

Will Apophis be visible to the naked eye in 2029?

Yes. During its 2029 flyby, Apophis will be visible to the naked eye from Europe, Africa and parts of Asia. It will appear as a bright point moving across the night sky.