In the next 200 years an asteroid will hit Earth: Will we be ready?

Earlier this spring, as violence and chaos drove thousands of refugees into the deadly waters around Italy, scientists gathered on the outskirts of Rome to discuss another sort of catastrophe. Astronomers and physicists from some of the world's top institutions grappled with a dire scenario: a 1,200-foot asteroid – large enough to cause epochal damage – was hurtling toward Earth, and the countries likely to be hit included some of the poorest and most unstable in the world. Policymakers bickered over whether to try to blow it up or move it, and nations nearly went to war over whether deflecting it would make the hurtling, fiery rock more likely to land on them.
But relax. It was only a drill. Had it been a real emergency, you would have been instructed to kiss the world – or a large chunk of it – goodbye.

Watching this week-long asteroid war game from the wings were two Americans, one from the scientific world and one from the military. These elder statesmen of what is called planetary defence have been responsible for reminding policymakers that the planet, and all life on it, has been shaped by big rocks from outer space slamming into it.

Dave Morrison was one of the first researchers to suggest that unlike the dinosaurs, made extinct by an asteroid impact, we humans might be able to defend ourselves. Former US Air Force Lt Colonel Lindley Johnson was put in charge of Nasa's planetary science division after suggesting in the 1990s that the Air Force track asteroids. He is now heading Nasa's NEO (Near Earth Object) Observations Program. These men are proud and relieved that the Big Question has evolved from what if a cataclysm-inducing space rock is aiming for us to what will we do about it?

That question was the main topic of that meeting held in a conference hall at Frascati in mid-April. The European Space Agency (ESA) had invited astronomers, physicists, nuclear engineers and mathematicians to discuss the slim possibility of a space rock smashing into Earth and causing regional damage or maybe even the end of civilisation. The goal was, as it has been for the last six Planetary Defence conferences, to share information about identifying asteroid threats and the methods for saving us all.

Scientists today can tell us, with various degrees of certainty, that an object is on track to smash the planet in, say, 200 years, and they believe that we probably have technology to stop it. But nobody knows how human beings could or would co-operate to face a global threat. And, in an age when many politicians deny man-influenced climate change, can we even count on them to believe the asteroid threat is real?

Dave Morrison, astronomer Carl Sagan's first doctoral student, was one of the first scientists to warn the public about asteroids in 1989 with Cosmic Catastrophes, a book he co-wrote with astronomer Clark Chapman. "Thirty years ago, there was no research on Near Earth Objects," he says. "There weren't that many known and hardly anything to study."
Since then, the field has grown to include national space agencies, the US Congress, the United Nations and labs filled with mathematicians, physicists, engineers, rocket scientists and even the designers of nuclear weapons. Thanks to their efforts, more than 150,000 asteroids are now registered with the Smithsonian museum's Minor Planet Center. The defenders estimate there are tens to hundreds of thousands more out there that we cannot see, many in our blind spot – hidden by the sun. About 12,700 of the identified ones are categorised as NEOs (Near Earth Objects, with orbits that come within 121 million miles of Earth's orbit). Nasa estimates that about 1,000 NEOs are civilisation-enders – larger than half a mile in diameter. None of the behemoths seems to be a likely threat but about 1,600 other mapped NEOs may be headed our way, and an impact could kill millions.

The Earth-crossers

The first comet was discovered in the 17th century – although comet-like objects have been sighted throughout history, showing up in biblical and other ancient accounts. The first asteroids were identified in the 19th century but it was not until the early 20th century that we realised that some of them actually cross Earth's orbit. Scientists now know there are thousands of "Earth crossers," and that luckily Jupiter and Saturn absorb many of the asteroids that might otherwise pummel Earth.

The late geologist Gene Shoemaker, a science prodigy who graduated from the California Institute of Technology at 19, was, in the 1950s, examining lunar craters for the US space programme when he determined that they were caused by impacts. Eventually, he was appointed head of the US Geological Survey Center of Astrogeology in Flagstaff, where he and his team began mapping asteroids and studying the mechanics of meteorite impacts. His most important find – in terms of planetary defence – was Comet Shoemaker-Levy 9, which smashed into Jupiter in 1994; it was the first extraterrestrial impact that human beings had first predicted and then witnessed in real time. And it convinced scientists that similar calculations could be made for Earth.

Around the same time, geologist Walter Alvarez discovered a layer of iridium-infused clay at the geological strata separating the Cretaceous and Tertiary periods – in other words, between the era of the dinosaurs and our epoch. Iridium is extremely rare on Earth, but common in meteorites. Geologists soon found a similar iridium layer at the same geological strata in other parts of the world and postulated that a catastrophic impact had occurred around the time the dinosaurs became extinct. Scientists even know where the asteroid that killed off the dinosaurs likely hit – just off the Yucatan Peninsula, at Chicxulub, Mexico.

In the decades since, geologists have learned more about how catastrophic extraterrestrial impacts changed our planet; they believe our moon is actually a chip off a collision between two Mars- and Venus-sized objects sometime during the Earth's first 100 million years. After that impact, the Earth was enveloped in a hot silicate atmosphere, leaving only heat-loving organisms in rocks a half-mile or more beneath the surface, and, from that, all future life developed. Numerous bigger objects, in the five- to 10-mile diameter range, like the one that caused the dinosaur extinction, have also slammed into the planet, causing lesser, but nevertheless catastrophic changes.
The Little Prince's asteroid

When Chapman and Morrison published their 1989 book about cosmic catastrophes they covered a broad range of menacing events including comets, asteroids and supernovas. But both men thought the asteroid impact scenario was the most intriguing because mankind could theoretically do something to prevent it happening. In 1990, Congressional staffers invited Morrison to present his findings about space rock hazards. A year later Congress authorised Nasa to study asteroids and how to deflect them.

Chapman and Morrison gathered together experts in astronomy, physics and geology to study the problem. The team concluded that the most dangerous asteroids are about one mile in diameter. Such a rock (one-10th the size of the one that erased the dinosaurs) could have "civilisation-ending" effects, mainly because weather alterations caused by impact-related dust would result in the starvation of billions of people. So they recommended sky surveys to find all objects of that size.
The planetary defender community also attracted nuclear weapons designers, about to be left unemployed by the end of the Cold War, who found a new market for their expertise. Among them was Dr Strangelove himself, Edward Teller, one of the fathers of America's nuclear weapons programme. Peace-loving Carl Sagan was also involved. The two men had argued bitterly over nuclear weapons but found common ground in the idea that nuclear weapons could save us from an asteroid. As chief of Nasa's asteroid programme. Johnson focused on asteroids and called his paper Preparing for Planetary Defence – thereby coining the term. After 23 years in the Air Force, Johnson announced he was retiring in 2003, and Nasa enlisted him to run its Near Earth Object Programme.

A third American played a pivotal role in the development of planetary defence. Russell "Rusty" Schweickart was the first Apollo astronaut to walk in space, on the Apollo 9 mission. In 2002, he founded the B612 Foundation (named after the asteroid in Antoine St Exupery's story The Little Prince). Schweikart devoted several decades to proselytising for deflection and mitigation technology. He also urged fellow astronauts to get involved and found some like-minded space explorers, including former astronaut Ed Lu, who now heads B612 Foundation. Schweickart has travelled the world encouraging a co-ordinated global response. "I fear there's not enough of a collective survival instinct to really overcome the centrifugal, political forces," he says. "That is, in a nutshell, the reason we'll get hit. Not because technically we don't know it's coming, or we can't do something about it."

Apophis, the un-creator

When an Indian Ocean tsunami killed 230,000 in 14 nations on 26 December 2004, it captured the world's attention and obscured a nearly simultaneous, albeit theoretical, brush with Armageddon. Just 48 hours before the disaster, scientists made an alarming calculation: an 885-ft-diameter hunk of dark space rock was heading our way, with a one in 25 chance of smashing into the Earth in 2036, an impact with the potential force of 58,000 Hiroshima A-bombs. The earthquake that launched the tsunami released less than half that force.

The ominous spinning rock was soon renamed Apophis, after a mythic Egyptian god, "the un-creator". By December 2004, astronomers at telescopes in Puerto Rico and Arizona had gathered enough data to enable scientists at the Jet Propulsion Lab in Pasadena, which tracks NEO orbits, to project that Apophis had a 2.4% chance of impact in 2029, and an alarming one in 25 chance of smashing the Earth on an orbital swing in 2036. Eventually scientists refined the prediction down to a much less likely threat of one in 250,000. When Apophis makes its close approach, it will pass between us and our satellites, and be visible to the naked eye.

For the planetary defenders, such an event is cause for glee, not alarm. The potential death star was a reason to wake up politicians and the public. The public imagination was already primed by a pair of Hollywood disaster movies in 1998 (Deep Impact and Armageddon) featuring annihilation from the skies. Now, with real apocalyptic catastrophe in the form of a killer tsunami in Indonesia, and a threat from an asteroid, people wanted answers.

The last significant asteroid event was one that no one saw coming. In 2013, a bus-sized space rock blew up in the sky near the town of Chelyabinsk, in Siberia, with a force similar to a nuclear bomb. Windows were blasted and 1,000 people went to hospital. Chelyabinsk gave the planetary defenders another lesson in what even a relatively small asteroid, bursting not on impact but in the air, can do. And they know it's only a matter of time before something like that happens over New York, London, Delhi or Tokyo.

Find them all!

The US Congress passed the George E Brown Act in response to the Apophis threat, and President Bush signed it into law in 2005, instructing Nasa to detect, track, catalogue and characterise the physical characteristics of asteroids larger than 85 miles across. (Brown had been a much-admired chairman of the House Science Committee, an early voice on climate change and near-Earth threats.) In other words, the US was finally doing what Morrison had been suggesting 15 years earlier: trying to find them all.

Objects as small as 150 yards across would cause severe regional damage, and the mapping project has only identified an estimated 25% of those. Geologists believe objects between about 50 and 150 yards in diameter hit the Earth every 100 to 300 years, and some have wreaked major havoc. Nasa is considering a proposal to build a new space-based telescope that will find and measure many more asteroids. If approved it could be operational by 2020.

Deflecting an asteroid is an embryonic science. There are three schemes, roughly classified as Nuke, Kick or Tug. The Nuke option would aim an explosive device – or, more likely, many devices – at an asteroid on a collision course. The planetary defence community regards that as a last-ditch effort. The other two options are the Kick – aiming a projectile called a "kinetic impactor" at an asteroid to knock it slightly off its orbit – and the Tug – an unmanned spacecraft shot into the orbit of the asteroid and operating as a "gravity tractor" with enough mass to pull the rock off its natural trajectory.

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About Arun Kumar Singh