What is Apophis?
Apophis is a near-Earth asteroid, meaning its orbit around the Sun brings it within 1.3 times the distance between the Sun and Earth. Its full name is Apophis 99942. After Apophis was discovered in 2004, the asteroid was given a 2.7% chance of hitting Earth in 2029, causing a great deal of media attention. It also for a time had a small chance of hitting Earth in 2036. Additional observations have shown it will not hit Earth in 2029 or in 2036.
Nevertheless, in 2029 Apophis will come closer to Earth than our geostationary communications satellites, likely sparking a great deal of public interest. The Planetary Society has submitted recommendations to the U.S. scientific community that identify science and outreach opportunities. We also present these recommendations at workshops and conferences.
How to pronounce Apophis
Apophis is pronounced uh-pah-fis, generally with an emphasis on the second syllable. Click here to listen to a recording.
What does Apophis mean?
In Egyptian mythology, Apophis was a serpent and the enemy of Ra, the sun god. Every night Apophis sought to bring eternal darkness on the world before being defeated by Ra at sunrise.
Who discovered Apophis?
Apophis was discovered on 19 June 2004, by Roy Tucker, David Tholen, and Fabrizio Bernardi at the Kitt Peak National Observatory in Arizona. Tucker was a 2002 grant recipient from our Shoemaker Near Earth Object Grant Program, which funds advanced amateur astronomers who find, track and characterize near-Earth objects.
How big is Apophis?
Like most asteroids, Apophis is too small for us to figure out its exact shape and size from Earth. Radar images have shown it measures 450 meters (1500 feet) across its longest axis, equivalent to about 5 football fields and taller than the Empire State Building in New York City. It is approximately 170 meters on its shortest axis. It is likely egg-shaped or even dual-lobed like Arrokoth, the small world NASA’s New Horizons spacecraft flew past in 2019.
Will Apophis hit Earth?
Not anytime soon. It definitely will miss Earth in 2029 and 2036, and radar observations of Apophis during the asteroid's flyby in March 2021 ruled out an impact for at least the next 100 years.
Why did the probability of Apophis impact in 2029 go up before it went down to zero?
Soon after its discovery, more observations of Apophis refined the asteroid’s trajectory, and the range of trajectories still included Earth. More observations refined its path around the Sun and excluded Earth, bringing the probability of a 2029 impact down to zero.
What would happen if Apophis hit Earth?
Apophis would cause widespread destruction up to several hundred of kilometers from its impact site. The energy released would be equal more than 1,000 megatons of TNT, or tens to hundreds of nuclear weapons.
How big was the asteroid that killed the dinosaurs?
The asteroid that led to the extinction of the dinosaurs as well as 70% of all species on Earth was at least 10 to 15 kilometers wide. It was much larger than Apophis, though millions of people could still die if an Apophis-sized asteroid struck a major metropolitan area.
How close will Apophis come to Earth in 2029?
On 13 April 2029 Apophis will pass as close as 30,600 kilometers (19,000 miles) above the Earth. If you’re superstitious, that's on a Friday the 13th.
How close will Apophis come to Earth in 2036?
On 30 March 2036 Apophis will pass Earth at a much further distance: 8.4 million kilometers (5.2 million miles). That’s more than 20 times the distance between the Earth and Moon.
Will we be able to see Apophis?
During the 2029 pass Apophis will be visible from Europe, Africa, and western Asia looking like a somewhat bright star (magnitude 3.1) moving rapidly across the sky. It will be much too far away to be visible without telescopes in 2036.
Will Apophis hit our geostationary communications satellites?
No. Apophis will pass closer to Earth than some of our geostationary
satellites, but its path will be inclined away from the equator and not
carry it through the region these satellites occupy.
How do astronomers determine if an asteroid like Apophis will hit Earth?
It’s not just enough to find asteroids—they must be tracked with
followup observations that measure where they are at different times.
These observations, which are performed by both professional and talented amateur astronomers around the world, are submitted to the Minor Planet Center. Groups at NASA’s Jet Propulsion Laboratory in the U.S. and the NEODyS program
in Italy compute asteroid orbits from those observations. The number
and quality of observations determines the uncertainty in predictions.
Sometimes when asteroids come close enough to Earth, radar is used to get more precise distance data that can be used to further refine their orbits. Occasionally, spacecraft visit near-Earth asteroids allowing even more precise orbits to be determined.
Could we stop an asteroid like Apophis?
With enough warning time before impact, meaning many years, we could change the orbit of an asteroid the size of Apophis enough to cause it to miss the Earth, but this would require a coordinated global effort. To learn more about planetary defense including deflecting asteroids see our planetary defense page or take our free, one-hour online class Asteroid Threat 101.
Is anyone planning a mission to Apophis?
NASA's OSIRIS-APEX mission will study the asteroid for 18 months starting in April 2029, just before it makes its close approach to Earth. OSIRIS-APEX is the repurposed OSIRIS-REx spacecraft that returned a sample of asteroid Bennu to Earth in September 2023.
OSIRIS-APEX will study how Earth's gravity changes Apophis' rotation rate and surface properties, which could help us understand what lies beneath the asteroid's surface. The mission will give us new insight into asteroids similar to Apophis, including how we might deflect one on course to hit Earth.
Did The Planetary Society advocate for an Apophis mission?
Yes! The Planetary Society called for missions to Apophis in our submission to the Planetary Science Decadal Survey. We also held a $50,000 Apophis mission design competition in 2007 and 2008 to design a mission that would “tag” Apophis to better know its orbit.
Where can I learn more about the asteroid threat?