Space agency scrambling as 'planet killer' asteroid headed for Earth
Asteroid 99942 Apophis is the size of a skyscraper and it's what we don't know that could kill us.
Are we staring down a cannonball? Or a shotgun shell? An armour-piercing warhead? Or a flash-bang grenade?
We know the asteroid 99942 Apophis, named after the ancient Egyptian God of Darkness and Chaos, is the size of a skyscraper. We know it’s moving relative to Earth at about 4.7 kilometres a second. We know it will narrowly miss Earth (by 23,000km) on Friday, April 13, 2029.
We don’t know much else.
And it’s what we don’t know that could kill us. Eventually.
Apophis is one of 25,000 near-Earth objects (NEOs) big enough to do substantial damage to our planet. Astronomers track them closely, and confidently declare none will hit us for at least 1000 years.
At least, none of the known ones. And we don’t really know all the forces at play.
That’s why the European Space Agency (ESA) is scrambling to raise enough cash to launch an Apophis probe mission in just four years.
And it hopes its RAMSES project can use existing technology to prove Earth can react quickly to an unexpected threat.
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Apophis will fall under Earth’s influence at less than one-17th the distance of the Moon.
Boulders may tumble. Dust may fly. Ravines may collapse - or open.
“Scientists could then use that knowledge to improve how we deflect asteroids in the future,” said The Planetary Society’s Asa Stahl.
“They could also get a better handle on the small forces that nudge asteroids’ orbits, refining their ability to predict if one might be on a collision course with Earth.”
Vital to know more about asteroids to stop impacts
“A large asteroid impact is potentially the only natural disaster humanity has the technology to predict years in advance and take action to prevent,” NASA’s Lindley Johnson states in a newly released summary of its most recent Planetary Defence exercise.
The scenario addressed a “planet killer” asteroid with a 72 per cent chance of hitting Earth within 14 years.
Things didn’t go so well.
“Better information about the asteroid would reduce uncertainties in the potential consequences of an impact, thereby enabling better decision-making about how to respond,” the summary states.
A solid lump of iron could prove impervious to impacts. So some form of space “tractor” may be needed.
And a loose clump of boulders could crumble if nudged, producing a “buckshot” effect.
NASA recommends developing an emergency-response capability to “rapidly launch an NEO reconnaissance mission”.
This, it adds, can be done by “repurposing existing spacecraft and/or instruments” to “rapidly gather information about an asteroid threat”.
Luckily, the ESO has just such a proposal up its sleeve: RAMSES.
Not all asteroids are created equal
There are three known types of asteroids whizzing past Earth.
C-TYPE: These lumps of clay and silicate are left over from the dust that formed the solar system.
S-TYPE: Clumps of nickel-iron and silicates drawn together over aeons.
M-TYPE: Bundles of metal (mostly nickel-iron). Some have been smelted into alloy ingots, or lava-coated iron cores.
Then there are comets. These can be either dirty snowballs or enormous clumps of frozen gas.
Astrophysicists say every threat will need an individually tailored approach.
And we’re about to experience why.
On September 26, 2022, NASA smashed its DART (Double Asteroid Redirection Test) spacecraft into the S-type asteroid Dimorphos at some 24,000km/h.
It was humanity’s first experiment at redirecting a potentially hazardous threat.
The impact nudged Dimorphos’ trajectory. But it also transformed the asteroid, ejecting dozens of large boulders and a cloud of pebbles into space.
Researchers believe those boulders will fall on Mars in the coming decades.
And a new study predicts the shrapnel cloud will begin to hit Earth’s atmosphere within seven years.
How planetary defence works against asteroids
“Several proposed planetary defence mitigation techniques are technically feasible, but none has been demonstrated in practice,” reads a recent US National Academies of Sciences, Engineering, and Medicine report.
“Each has its own advantages and disadvantages depending on the physical characteristics of the NEO and the available warning time to impact.”
Less time requires a more dramatic response. Which generates greater risk.
“Deflections can be applied using impulsive or 'fast push' methods like a kinetic impactor or a standoff nuclear explosion, or via 'slow push/pull' methods such as a gravity tractor or ion beam deflection,” the report states.
Kinetic impact isn’t likely to be effective against larger objects. And there is always the risk deadly fragments will remain on course.
Nuclear detonation will vaporise an asteroid’s surface, creating orbit-altering momentum. But they must be precisely positioned to have any effect.
Ion Beam deflection involves a spacecraft sitting close to the asteroid, spraying its surface with thrusters. But will this push an asteroid, or just blow off dust?
A gravity tractor would involve a spacecraft sitting so close to an asteroid that its gravitational attraction pulls it off course. But the asteroid’s composition will again produce different outcomes.
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