It’s the most famous asteroid in the history of astronomy. It’s big. It’s solid. And in less than five years, Apophis, the “God of Chaos,” will come particularly close to Earth.
It will not work.
But that didn’t always seem to be the case.
When it was discovered in 2004, early orbital calculations of asteroid 99942 Apophis placed Earth in a “danger zone” for collisions during its passes in 2029 and 2036.
Apophis is a mass of rocks about 350 meters in diameter, roughly the size of a modern luxury cruise liner or one of America’s massive nuclear-powered aircraft carriers.
If it hit land, it could destroy an area the size of a country. An impact at sea would trigger devastating tsunamis.
Satellite images track Apophis.Satellite images track Apophis.
Astronomers have been closely tracking the movements of Apophis since its discovery 20 years ago. Credit: NASA/JPL-Caltech and NSF/AUI/GBO
But additional observations and radar measurements have since considerably refined its orbital projections.
We now know that on April 13, 2029, it will miss Earth by 32,000 kilometers.
And the calculations are good enough to rule out any risk for the next 100 years.
But the geostationary satellites that power your cell phone’s GPS are 35,800 km away, and the Moon is 384,400 km away.
So, from a cosmic perspective, Apophis is still going to be a very close opponent.
This is why the European Space Agency (ESA) wants to observe it carefully during its flight.
Menacing asteroid named after Chaos God
Apophis is named after the ancient Egyptian god of darkness and chaos, a god who was constantly at war with Ra (the sun god).
ESA wants to send RAMSES – named after the pharaoh priest-kings of Egypt – to intercede on behalf of humanity. (It also stands for Rapid Apophis Mission for Space Safety.)
As part of the Planetary Defense Program, the mission is to better understand the composition and behavior of the more than 1,000 “planet-killer” asteroids known to pass through Earth’s orbit.
And the short time frame (four years is a minimum for a space project) is not entirely accidental.
ESA presents this challenge as a “best practice” for a potential real-world scenario.
Astronomers estimate that about 95 percent of all “planet-killer” asteroids have been located. It’s the missing 5 percent that worries them.
Apophis depicted as a giant serpent fighting Ra, the sun god, in an Egyptian artwork.Apophis depicted as a giant serpent fighting Ra, the Sun God, in an Egyptian artwork.
In ancient Egyptian artwork, Apophis is often depicted as a serpent or dragon battling the sun god Ra. Source: Getty
Such an event could happen out of nowhere, at any time. The odds of such an impact are a crapshoot.
About 1.4 million asteroids have been discovered floating around the solar system. Most of them are located between the orbits of Mars and Jupiter.
But some have swung into more extreme trajectories, sending them plummeting toward the Sun — through the orbits of the inner planets, including Earth.
A review of all known threatening asteroid orbits was recently completed.
“This is good news,” says astronomer Oscar Fuentes-Muñoz of the University of Colorado at Boulder. “As far as we know, there won’t be an impact in the next 1,000 years.”
However, this only applies to large asteroids, known as “planet killers.” Others, such as Apophis, still have the potential to vaporize an area several hundred kilometers in diameter.
According to the Planetary Society, that would be the equivalent of 1,000 megatons, or hundreds of nuclear warheads all exploding in the same place.
What risk do asteroids pose to Earth?
The Earth passes through about 10 tons of interplanetary dust every day. These are the meteors you see almost every night.
Some, about the size of a pebble or a bowling ball, enter the atmosphere three or four times a day, causing the brightest flashes in the night sky.
A truck-sized fire occurs two to three times a century. The most recent was in 2013, when a massive fireball shattered windows and injured pedestrians above the city of Chelyabinsk, Russia.
The largest, about 150 m in diameter, are potentially devastating. But the probability of such a device entering the atmosphere is about once every 25,000 years.
Radar images of the asteroid Apophis, captured in 2012.Radar images of the asteroid Apophis, captured in 2012.
Scientists used radar images to determine that Apophis would not hit Earth. Credit: NASA/JPL-Caltech
A collision with an object larger than a kilometer could end civilization as we know it, causing tsunamis, fireballs, and huge clouds of debris to be thrown high into the atmosphere. The probability of such an event occurring is about once every two million years.
The killer dinosaur that struck 66 million years ago is estimated to have measured about 10km in diameter.
‘Nature brought us one’: asteroid expert
To speed up the RAMSES mission, ESA is proposing to reuse the basic design of an asteroid mission already in preparation.
The Hera probe is scheduled to be launched in October. Its mission will be to revisit the double asteroids Didymos and Dimorphos, the subjects of an impact experiment in 2022.
RAMSES would take advantage of Apophis’ close passage to closely observe how its rocky surface is held together. This means that the consequences of the asteroid’s close encounter with Earth’s gravity could be observed.
Artist's impression of NASA's OSIRIS-APEX probe approaching the surface of the asteroid Apophis.Artist's impression of NASA's OSIRIS-APEX probe approaching the surface of the asteroid Apophis.
Scientists plan to study the asteroid as it passes close to Earth. Source: NASA
“For the first time, nature has brought us one and conducted the experiment itself,” said ESA astronomer Patrick Michel.
NASA’s OSIRIS-REx probe (Osiris being the Egyptian god of the dead) recently sent samples from the asteroid Bennu to Earth. It is currently following an arc through space to reach Apophis about a month after its 2029 Earth pass. It is expected to remain nearby for more than a year.
One of its missions will be to explode the surface of Apophis with one of its thrusters.
“This will allow us to observe subsurface materials, which will provide previously inaccessible information on space weathering and surface strength of stony asteroids,” say mission planners from the University of Arizona.
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