It is the most famous asteroid in astronomy. It’s big. It’s stable. And in less than five years, Apophis – the “God of Chaos” – will come especially close to Earth.
It won’t hit.
But it hasn’t always seemed that way.
When it was first discovered in 2004, initial orbital calculations for asteroid 99942 Apophis placed Earth in the “danger zone” of a collision during its 2029 and 2036 transits.
Apophis is a cluster of rocks with a diameter of about 350 meters. That’s roughly the size of a modern luxury cruise ship or one of America’s huge nuclear-powered aircraft carriers.
If it hits land, it can destroy an area the size of a country. A blow from the sea would unleash devastating tsunamis.
But additional observations and radar sweeps have since greatly refined his orbital predictions.
We now know that on April 13, 2029, it will miss Earth by 32,000 kilometers.
And the math is good enough to rule out any risk for another 100 years.
But the geostationary satellites powering your mobile phone’s GPS are 35,800 km away. And the Moon is at a distance of 384,400 km.
So, cosmically, Apophis will still be very close.
That’s why the European Space Agency (ESA) wants to take a good look at it as it ejects.
A menacing asteroid named after the God of Chaos
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 Egyptian pharaoh-priest-kings – to intercede on behalf of humanity. (It also stands for Rapid Apophis Mission for Space Safety).
Part of the Planetary Defense Program, the mission is to better understand the structure and behavior of the more than 1,000 “planet killer” asteroids known to shoot through Earth’s orbit.
And the short notice (four years is the minimum for a space project) is not entirely accidental.
ESA presents the challenge as a “good practice” for a potential real-world scenario.
Astronomers estimate that about 95 percent of all “planet killer” asteroids are localized. The missing 5 percent is what worries them.
A person can appear out of nowhere at any time. The odds of such an impact are a roll of the dice.
About 1.4 million asteroids have been found floating around the solar system. Most are clustered between the orbits of Mars and Jupiter.
But some have fallen into more extreme trajectories, sending them diving toward the Sun — through the orbits of the inner planets, including Earth.
A review of all known threat asteroid orbits was recently completed.
“Good news,” says University of Colorado Boulder astronomer Oscar Fuentes-Muñoz. “As far as we know, there is no impact for the next 1,000 years.”
However, this only applies to huge “planet killer” asteroids. Others – such as Apophis – still have the potential to vaporize an area of several hundred kilometers.
According to the Planetary Society, this would be equivalent to 1,000 megatons, or hundreds of nuclear warheads, all fired at the same location.
What risk do asteroids pose to Earth?
Earth passes through approximately 10 tons worth of interplanetary dust per day. These are the meteors you see almost every night.
Some, ranging from the size of pebbles to bowling balls, enter the atmosphere three or four times each day. They cause the brightest lightning in the night sky.
Something the size of a truck arrives two to three times every century. The latest hit in 2013 was the massive fireball that shattered windows and injured pedestrians over the city of Chelyabinsk, Russia.
The large ones – about 150m in diameter – are potentially devastating. But the chances of one entering the atmosphere are about one in 25,000 years.
An impact from something over 1km in size could end civilization as we know it with tsunamis, fireballs and huge clouds of debris thrown high into the atmosphere. The chances of one of them arriving are about once in two million years.
The killer dinosaur that struck 66 million years ago is thought to have been about 10 kilometers in diameter.
‘Nature brought us one’: Asteroid expert
To accelerate the RAMSES mission, ESA proposes to reuse the basic design of an asteroid mission already in preparation.
The Hera probe is due to launch in October. Its task is to re-examine the twin asteroids Didymos and Dimorphos, subjects of an impact experiment in 2022.
RAMSES would have taken advantage of Apophis’ close pass to get a good look at how its stone surface held together. And this means that the consequences of the asteroid’s close encounter with Earth’s gravity can be observed.
“For the first time, nature has brought one to us and is conducting the experiment itself,” said ESA astronomer Patrick Michel.
NASA’s OSIRIS-REx probe (Osiris is the Egyptian god of the dead) recently sent samples from the asteroid Bennu back to Earth. It is now making its way through space to rendezvous with Apophis about a month after it passes Earth in 2029. It is expected to remain in close proximity for more than a year.
One of its missions will be to blast the surface of Apophis with one of its thrusters.
“This will allow us to observe subsurface material, providing otherwise unavailable insight into the space weathering and surface strength of rocky asteroids,” say University of Arizona mission planners.
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