Apophis — inside the satellite belt
On 13 April 2029 the asteroid Apophis, about 340 m across on average, will pass roughly 32,000 km above Earth's surface, closer than the geostationary satellites. From Europe, Africa and western Asia it should be bright enough to see without a telescope.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
On 13 April 2029 the asteroid Apophis is due to pass very close to Earth. Apophis is shaped a little like an elongated peanut, and it is about 340 metres across on average. At its closest it will be about 32,000 km above Earth's surface. The geostationary satellites that carry television and weather data orbit about 36,000 km up, so Apophis will pass inside their ring.
Calculations suggest that an asteroid of this size comes this close only about once every 800 years on average. This time, however, the date and even the hour have been known for decades. That has given scientists years to prepare, and telescopes and spacecraft from several countries are planning their work around this one day.
Apophis was not always a welcome visitor. Soon after it was discovered in 2004, the first rough orbit gave it a 2.7 percent chance of hitting Earth in 2029. As more observations came in, that chance disappeared. Radar measurements in 2021 then showed that it will not hit Earth for at least the next 100 years.
The name comes from Apophis, the serpent of chaos in Egyptian mythology who tried to swallow the Sun. It is a reminder of how worried people were at the time of discovery. Today the 2029 pass is seen as a chance for science rather than a danger. ESA's Ramses spacecraft is planned to reach Apophis before the flyby, and NASA's OSIRIS-APEX shortly after it.
Mission goals
The encounter matters to science because Earth itself becomes a giant piece of laboratory equipment. Scientists think that small asteroids like Apophis are not solid lumps of rock but rubble piles: collections of boulders and gravel held together loosely by their own weak gravity. When such an object passes close to Earth, our planet's strong pull could change its shape or the way it spins.
Earth pulls a little harder on the near side of the asteroid than on the far side. That difference stretches the asteroid slightly. It may speed up or slow down its spin, tilt its axis, or make loose rocks slide down its slopes. These effects have been studied in many computer models, but they have hardly ever been measured. Nobody can drag an asteroid close to Earth on purpose, so nature is running the experiment for us.
The results will also help with planetary defence. If an asteroid is ever found heading for Earth, experts will need to know how solid it is before deciding whether to push it aside or break it up. In 2022 the DART spacecraft tested the first idea by crashing into a small asteroid and changing its orbit. Apophis offers a different test, one in which scientists simply watch and touch nothing.
Mission chronology and background
Apophis was discovered in June 2004 at Kitt Peak Observatory in Arizona and was first known by the provisional name 2004 MN4. For several months the observations covered only a short stretch of its orbit, so the orbit was uncertain. Each new calculation raised the chance of a 2029 impact, and in December 2004 it reached level 4 on the Torino Scale, which rates asteroid hazards. No other object has ever been rated higher.
What changed things was a set of older pictures. Astronomers found Apophis in images taken in March 2004, before its official discovery. With a longer record of its motion, the orbit became much more precise, and the chance of a 2029 impact fell to zero. The episode showed how a probability can jump up and then vanish when data are scarce, and it pushed experts to think about how to explain such cases to the public.
The 2029 pass will also change Apophis's orbit. Today it circles the Sun once every 0.89 years or so; after Earth's gravity tugs on it, the period is calculated to become about 1.16 years. Apophis will pass Earth again in 2036 and 2068, but nowhere near as closely as in 2029. Instead, two spacecraft are planned to study it before and after the flyby, although their schedules could still change.
Other milestones of this mission
- OSIRIS-APEX arrives at Apophis(planned)
Where to see it — sky and simulator
Apophis makes its closest approach at about 21:46 Universal Time on 13 April. At that hour the sky is dark over Europe, Africa and western Asia, where the asteroid is expected to reach about third magnitude, similar to an ordinary star in a constellation. From a place away from bright city lights it should be visible without any equipment. In East Asia and Australia it will already be the morning of 14 April, and across North America it will still be daytime, so a naked-eye view there is not realistic.
Unlike an eclipse, there is no danger to your eyes. You are looking at a point of light in the night sky, so no filter is needed, and binoculars simply make it easier to find. Do not expect a bright streak like a meteor. Apophis will look like a star, but over a few minutes that star will visibly shift among the stars around it. That movement is the sign of how close it is.
Even if you cannot see it in the sky, you can follow the event in NowSky's orbit view. Move the time to 13 April 2029 and the replay shows Apophis diving inside the ring of geostationary satellites, then being bent by Earth's gravity onto a new path. The exact timing and the track across the sky will be refined as the date gets closer.
See this for yourself — replay the moment in the orbit view
FAQ
Is there any chance Apophis will hit Earth?
No. Radar observations in 2021 made the orbit very precise, and they rule out an impact for at least the next 100 years, including 2029 and the 2068 pass that once caused concern. The 2.7 percent figure from 2004 came from an early orbit based on very few observations.
Will it really be visible to the naked eye?
It is expected to be, from places where it is night at closest approach, such as Europe, Africa and western Asia. It should reach about third magnitude, which is visible without equipment from a dark site. Binoculars make its motion among the stars much easier to notice. In East Asia and Australia it will be morning, and in North America daytime, so it will be hard to see there.
It passes inside the satellite ring, so why won't it hit a satellite?
The geostationary ring is an enormous circle around Earth, and the satellites along it are spaced far apart. Apophis's path is also known very precisely, so the chance of hitting a satellite is tiny. Satellite operators will still keep an eye on the pass.
Will the flyby change the asteroid itself?
Scientists think it might. Models suggest that Earth's gravity could change how Apophis spins or cause small landslides on its surface, but only observations can show how large the changes are. That is why spacecraft are planned to visit it both before and after the flyby, so the two views can be compared.
Related
- OSIRIS-APEX arrives at Apophis
- DART — the first planetary defence test
- Hera arrives at Dimorphos
- Hera — object index
- Earth — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.