It is the most notorious asteroid in astronomy. It is big. It is massive. And in less than five years, Apophis – the “God of Chaos” – will come particularly close to Earth.
It won’t hit.
However, it did not always seem that way.
When the asteroid 99942 Apophis was discovered in 2004, initial orbit calculations showed that the Earth would be in a collision “danger zone” during its flybys in 2029 and 2036.
Apophis is a lump of rock about 350 meters in diameter, roughly the size of a modern luxury cruise ship or one of America’s giant nuclear-powered aircraft carriers.
If it hits land, it could destroy an area the size of a country. If it hits the sea, it would trigger devastating tsunamis.
However, thanks to additional observations and radar tracking measurements, the orbit projections have since been considerably refined.
Today we know that it will miss the Earth by 32,000 kilometers on April 13, 2029.
And the mathematics is good enough to eliminate any risk for the next 100 years.
But the geostationary satellites that power your phone’s GPS are 35,800 km away. And the moon is 384,400 km away.
So, cosmically speaking, it will still be a very close call to defeat Apophis.
That is why the European Space Agency (ESA) wants to take a closer look at the star that catapulted past.
Threatening 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 god of the sun).
ESA wants to send RAMSES – named after the Egyptian priest-kings, the Pharaohs – to work on behalf of humanity. (This is also the abbreviation for Rapid Apophis Mission for Space Safety.)
The mission is part of the Planetary Defense Program and is designed to help better understand the composition and behavior of the more than 1,000 “planet-killer” asteroids known to shoot through Earth’s orbit.
And the short time span (four years is the minimum for a space project) is not entirely coincidental.
ESA presents the challenge as a “best practice” for a possible real-world scenario.
Astronomers estimate that about 95 percent of all “planet-killing” asteroids have been located. What worries them is the missing 5 percent.
Such an impact could appear out of nowhere at any time. The probability of such an impact is a gamble.
About 1.4 million asteroids have been discovered orbiting the solar system, most of them between the orbits of Mars and Jupiter.
Some, however, have taken more extreme trajectories and plunged toward the Sun – via the orbits of the inner planets, including Earth.
A review of all known threatening asteroid orbits was recently completed.
“Good news,” says astronomer Oscar Fuentes-Muñoz of the University of Colorado Boulder. “As far as we know, there will be no impact in the next 1,000 years.”
However, this only applies to giant asteroids that can destroy planets. Others – such as Apophis – still have the potential to vaporize an area several hundred kilometers in diameter.
According to the Planetary Society, this would be equivalent to 1,000 megatons, or hundreds of nuclear warheads, all detonated in the same place.
What risk do asteroids pose to the Earth?
The Earth passes through about 10 tons of interplanetary dust every day. These are the meteors you see almost every night.
Some of them, ranging in size from a pebble to a bowling ball, enter the atmosphere three to four times a day, causing the brightest flashes in the night sky.
Something as large as a truck hits two or three times a century. The last impact was in 2013 – a massive fireball that shattered windows and injured pedestrians over the Russian city of Chelyabinsk.
The large ones, with a diameter of about 150 m, are potentially devastating, but the probability of one of them entering the atmosphere is about 1 in 25,000 years.
An impact of just over 1 km in size could destroy civilization as we know it, with tsunamis, fireballs, and huge clouds of debris hurled high into the atmosphere. The probability of something like this happening is about once every two million years.
The dinosaur killer that struck 66 million years ago is said to have had a diameter of about 10 kilometers.
“Nature brings us one”: Asteroid expert
To speed up the RAMSES mission, ESA proposes to reuse the basic design of an asteroid mission already in planning.
The launch of the Hera probe is scheduled for October. Its task is to revisit the binary asteroids Didymos and Dimorphos, which will be the subject of an impact experiment in 2022.
RAMSES would use the close flyby of Apophis to take a closer look at how its rocky surface is held together, meaning the effects of the asteroid’s close encounter with Earth’s gravity could be observed.
“For the first time ever, nature brings us one and conducts the experiment itself,” said ESA astronomer Patrick Michel.
NASA’s OSIRIS-REx probe (Osiris is the Egyptian god of death) recently sent samples of the asteroid Bennu to Earth. It is now moving along a curved path 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 engines.
“This will allow us to observe subsurface material, giving us otherwise inaccessible insights into space weathering and the surface strength of rocky asteroids,” say mission planners at the University of Arizona.
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