It’s astronomy’s most notorious asteroid. It’s big. It’s solid. And, in less than five years, Apophis – the “God of Chaos” – will come especially close to Earth.
It won’t hit.
It didn’t always seem that way, though.
When first discovered in 2004, initial orbital calculations for asteroid 99942 Apophis put Earth in a collision “danger zone” during its 2029 and 2036 passes.
Apophis is a clump of rocks about 350 metres across. That is about the size of a modern luxury cruise liner, or one of America’s enormous nuclear-powered aircraft carriers.
If it struck land, it could destroy an area the size of a country. A sea impact would unleash devastating tsunamis.
But additional observations and radar ranging have since considerably refined its orbital projections.
We now know that, on April 13, 2029, it will miss Earth by 32,000 kilometres.
And the math is good enough to rule out any risk for a further 100 years.
But the geostationary satellites power the GPS on your mobile phone are at 35,800km. And the Moon is 384,400km distant.
So, cosmically speaking, Apophis is still going to be a very close call.
Which is why the European Space Agency (ESA) wants to take a good look as it catapults by.
Menacing asteroid named after God of Chaos
Apophis is named after the ancient Egyptian God of Darkness and Chaos – a god that was constantly warring with Ra (the God of the Sun).
The ESA wants to send RAMSES – named after Egypt’s priest-king Pharaohs – to intercede on humanity’s behalf. (It’s also short for Rapid Apophis Mission for Space Safety).
Part of the Planetary Defence Program, the mission is to better understand the makeup and behaviour of the more than 1,000 “planet killer” asteroids known to cannon through Earth’s orbit.
And the short notice (four years is minimal for a space project) isn’t entirely accidental.
The ESA presents the challenge as a “good practice” for a potential real-world scenario.
Astronomers believe about 95 per cent of all “planet killer” asteroids have been located. It’s the missing 5 per cent that has them worried.
One could come out of nowhere, at any time. The odds of such an impact are a game of dice.
Some 1.4 million asteroids have been found floating around the solar system. Most are bundled between the orbits of Mars and Jupiter.
But some have tumbled into more extreme trajectories, sending them diving towards the Sun – across the orbits of the inner planets, including Earth.
A review of all known threatening asteroid orbits has recently been completed.
“Good news,” says astronomer Oscar Fuentes-Muñoz of the University of Colorado Boulder. “As far as we know, there’s no impact in the next 1,000 years.”
This, however, applies only to enormous “planet killer” asteroids. Others – such as Apophis – still have the potential to vaporise an area several hundred kilometres across.
According to the Planetary Society, this would be the equivalent of 1,000 megatons, or hundreds of nuclear warheads all set off in the same place.
What risk to asteroids pose to Earth?
Earth passes through roughly 10 tonnes worth of interplanetary dust daily. 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. These cause the brightest flashes in the night sky.
Something the size of a truck arrives two to three times each century. The last hit in 2013 – the massive fireball that smashed windows and injured pedestrians over the city of Chelyabinsk, Russia.
The big ones – about 150m across – are potentially devastating. But the odds of one entering the atmosphere are about one in every 25,000 years.
A hit by something over 1km in size could end civilisation as we know it through tsunamis, fireballs and vast clouds of debris being thrown high into the atmosphere. The odds of one of these arriving is once every two million years or so.
The dinosaur killer that hit 66 million years ago is believed to have been about 10km across.
‘Nature bringing one to us’: Asteroid expert
To speed up the RAMSES mission, the ESA proposes to reuse the basic design of an asteroid mission already in the pipeline.
The Hera probe is due to be launched in October. Its job is to revisit the double asteroids Didymos and Dimorphos, the subjects of an impact experiment in 2022.
RAMSES would take advantage of Apophis’ close pass to take a good look at how its stony surface is held together. And that means the consequences of the asteroid’s close encounter with Earth’s gravity can be observed.
“For the first time ever, nature is bringing one to us and conducting the experiment itself,” ESA astronomer Patrick Michel said.
NASA’s OSIRIS-REx probe (Osiris being the Egyptian god of the dead) recently sent samples of the asteroid Bennu back to Earth. It’s now arcing its way through space to rendezvous with Apophis about a month after it passes Earth in 2029. It’s expected to stay in close proximity for more than a year.
One of its missions will be to blast Apophis’ surface with one of its thrusters.
“This will allow us to observe subsurface material, which will provide otherwise inaccessible insight into space weathering and the surface strength of stony asteroids,” say the University of Arizona mission planners.
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