The asteroid of 13 April 2029
Apophis
On 13 April 2029 Apophis, an asteroid about 340 metres across, will pass about 32,000 km above Earth's surface: closer than the satellites that broadcast television. It will be visible to the naked eye from Europe and Africa, and it will not hit Earth. For a body this size, such an event happens on average once every few thousand years.
- Diameter
- 340 m
- Distance from Sun
- 138 M km
- Orbital period
- 324 days
- Rotation
- 30.6 hours
- Discovered
- 2004
- Next flyby
- 13 April 2029
Physical characteristics
Apophis has a mean diameter of about 340 metres, more than the height of the Eiffel Tower, and it is elongated: radar images show two lobes, like a peanut. It is a rocky S-type asteroid, similar in composition to the most common meteorites, and reflects about a third of the light it receives.
It does not spin about a fixed axis: it tumbles with a complex motion whose main period is about 30.6 hours. The 2029 flyby will almost certainly change that motion, and could trigger small landslides on the surface: this is one of the things the spacecraft will go and check.
Orbit and rotation
Today Apophis takes 324 days to travel an orbit lying between 0.75 and 1.10 AU from the Sun, 138 million km on average: most of the time it stays inside Earth's orbit, which is why it is classed among the Atens. The 2029 flyby will change that: Earth's gravity will widen its orbit, its period will rise to about 1.2 years and Apophis will become an Apollo asteroid.
On 13 April 2029, at 21:46 UTC, it will pass about 38,000 km from Earth's centre, that is, about 32,000 km above the surface, inside the ring of geostationary satellites. It will reach about magnitude 3 and cross the sky in a few hours, visible to the naked eye from Europe, Africa and western Asia. Radar observations in 2021 ruled out any possibility of impact for at least a hundred years.
Discovery and exploration
Roy Tucker, David Tholen and Fabrizio Bernardi discovered it on 19 June 2004 from Kitt Peak Observatory in Arizona. In December of that year the first calculations gave a 2.7% chance of impact in 2029, the highest ever assigned to an asteroid, and Apophis reached level 4 on the Torino scale. Within days, older observations found in the archives ruled the collision out. Its name is the Greek form of the Egyptian serpent Apep, enemy of the Sun.
Two missions will follow it through the flyby. NASA's OSIRIS-APEX, the same spacecraft that brought back the Bennu samples, will reach it just after its encounter with Earth and stay alongside for about a year and a half. Europe's Ramses mission, developed with Japan, is due to launch in spring 2028 to arrive in February 2029, two months ahead, and observe the asteroid before, during and after the flyby.
Frequently asked questions
Will Apophis hit Earth in 2029?
No. It will pass about 32,000 km above the surface, a distance known to within a few kilometres. Radar observations in March 2021 also ruled out an impact on later passes, including the one in 2068, for at least a hundred years.
Will Apophis be visible to the naked eye?
Yes, under a clear, dark sky. On the evening of 13 April 2029 it will look like a moderately bright star, about magnitude 3, moving fast: it will cross much of the sky in a few hours. It will be visible from Europe, Africa and western Asia, to about two billion people.
What will happen to the asteroid during the flyby?
Earth's gravity will change its orbit, moving it from the Aten group to the Apollo group, and will almost certainly alter its rotation. Tidal forces could also disturb the surface, causing small landslides and exposing fresh material. There will be no effect on Earth.
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