Defending Earth

"This plan is an outline not only to enhance the hunt for hazardous asteroids, but also to better predict their chances of being an impact threat well into the future and the potential effects that it could have on Earth."
"[Protecting Earth from incoming asteroids will be a huge job, no astronauts would be involved.] That's something relegated to the movies — it makes a good movie, but we do not see in our studies any technique that would require the involvement of astronauts. [NASA's proposed asteroid-deflection techniques] would all be done by robotic spacecraft."
"[The agency's Double Asteroid Redirection Test [DART], to be launched in 2021, will be] our first technology demonstration of the kinetic impact technique to deflect an asteroid."
NASA's planetary defense officer, Lindley Johnson

"[One focus of the DART goal is to increase international cooperation to better prepare the rest of the world for the possibility of an asteroid strike — under the leadership of the United States.]"
"This kind of cooperation is really important  It's a global hazard that we all face together, and the best way to approach and address that hazard is cooperatively."
Aaron Miles, senior policy adviser, White House Office of Science and Technology Policy

Artist's illustration of a large asteroid headed for Earth. Credit: ESA

A report from the National Science and Technology Council in the United States outlined a pressing need to improve vigilance by the international community dedicated to preserving Planet Earth's geological integrity and the safety of all living creatures, through international programs in coordination with the United States in detecting the presence of and danger posed by asteroids and other space objects speeding toward Earth, recognizing that a collision with a large rock-metal-ice object hurtling toward the planet could result in utter catastrophe.

During Earth's formative years tens of millions of years ago such collisions did occur when for example a 200-kilometre-wide crater was discovered, all that remained of the results of such an ancient collision that wiped out three-fourths of the vegetation and animal species then existing on the planet. The crater's remnants were recognized on the Yucatan Peninsula, and the Gulf of Mexico, a wide swathe of utter destruction.

The knowledge that Earth is vulnerable at any given time to other collisions which might occur have been fortified by some that have. As, for example in 2013's event when a 20-metre asteroid appeared suddenly over the sky in Chelyabinsk, Russia, exploding and damaging thousands of buildings in the thermal blast, causing widespread injuries. In 1908 a much larger asteroid exploded over Tunguska, Russia leaving 2,000 square kilometres of forest devastated.

The report, published in Science, pointed out that were such an asteroid to explode over a far more vulnerable, populated area such as New York City, the fallout would be enormous, the death toll unspeakably dramatic. NASA has catalogued no fewer than 18,310 space objects of sizes from minuscule to alarmingly huge. Just over 800 of those space objects are 140 metres or larger. Should a space rock happen to suddenly appear  and an estimate made of its strike time; anywhere from days to weeks in advance, current space technology offers no solutions for stopping or altering its trajectory.

The National Science and Technology Council report speaks of the urgent need to improve asteroid detection, its tracking and the potential for deflection. Its participating partners are NASA, federal emergency, the military, the White House and other similar U.S. national authorities. Scientists, according to NASA's planetary defence officer, have discovered 95 percent of near-Earth objects measuring one kilometre or larger, continuing to search for the remaining 5 percent and smaller objects still capable of inflicting damage on Earth.

The most difficult to detect are rocks that have passed the sun and are on their way out of the solar system, approaching from the day side, while ground telescopes are known to detect asteroids speeding into the inner solar system, approaching from the night side of Earth; the former is how the Chelyabinsk asteroid suddenly appeared. The nightmare scenario of a Tunguska-sized asteroid hitting New York City equates to millions of people dying.

Even with all resources put to work, headed by the American initiative and joined by international partners with every reason to be as concerned as the U.S., solutions will take years of planning, design, construction and implementation before it could be said an effective defence can be mounted. It would take years for any effort to turn away a threatening asteroid; a number of years to build a spacecraft, another few years for it to reach its target. A minimum ten years' advance notice of a feared approach of a killer asteroid is what Dr. Johnson envisions.

The mission could be comprised of a design to smash the asteroid or comet with a fast-moving robotic spacecraft to alter the path of the threat. Even to launch a nuclear device to superheat the surface of the asteroid, to remove sufficient material to make for a swerving diversion, thus bypassing its initial target Earth. It all sounds dramatically science-fiction-like, but then so does the prospect of our home, Earth, or parts thereof being blown to smithereens by some gigantic space object approaching and colliding  and destroying it and us.

This image of a vapor trail was captured about 125 miles (200 kilometers) from the Chelyabinsk meteor event, about one minute after the house-sized asteroid entered Earth’s atmosphere.

Credits: Alex Alishevskikh