The US Government has announced a 10-year project to increase its readiness for preparing for and preventing catastrophic asteroid impacts.
The project, and the threat assessment, are outlined in a new report released under the seal of the US President’s National Science and Technology Council. The multi-author document is the product of the Interagency Working Group for Detecting and Mitigating the Impacts of Earth-Bound Near-Earth Objects (yielding the faintly disturbing acronym, DAMIEN), which includes high-level representatives from several government agencies, including NASA, the US Air Force, the Department of Defence and the State Department.
“Unlike most natural disasters, asteroid impacts are preventable,” says Aaron Miles, of the White House Office of Science and Technology Policy.
But it’s probably not a job for President Trump’s newly announced Space Force.
“The responsibility for responding and preparing is spread throughout the US government,” Miles says.
“Everyone brings capabilities to the table, and one of the objectives is to make sure we leverage those capabilities wherever they are.”
In fact, much of the work is already being carried out by a multitude of federal, state, and international agencies, including the United Nations.
Nor is NASA envisioning sending astronauts on risky missions to blow up an approaching asteroid. That makes for a good movie, says Lindley Johnson, NASA’s planetary defence officer, but it’s not practical in the real world. The type of missions involved would take years, and would best be handled by robotic spacecraft that can sustain a multi-year trip to a threatening asteroid.
The process begins by identifying as many near-Earth asteroids as possible. Already, Johnson says, NASA and its partners have found and tracked 95-to-96% of asteroids one-kilometre or larger suspected to sometimes pass within 48 million kilometres (30 million miles) of Earth.
“We think there are about 40 more that may need to be found,” he says.
In addition, he explains, astronomers are seeking smaller asteroids, with a goal of someday finding everything larger than 140 metres in diameter — a size large enough to have serious regional impacts if it were to strike Earth.
So far, Johnson says, a total of 18,310 near-earth asteroids have been found, of which about 8000 are in the 140-metre-plus size range. Again, none of them pose an immediate risk. But those that are known are probably just the tip of the iceberg. It is likely that two-thirds of bodies the 140-metre-plus size have yet to be spotted.
If a dangerous asteroid is detected far enough in advance, he says, there are three ways in which it can be deflected using presently feasible technologies.
One, which may be tested as early as 2021 to 2022 on a small, non-threatening asteroid called Didymos is to hit the asteroid with a “kinetic impactor.” This would be a rocket that would simply slam into it like a giant cannonball, hitting it hard enough to knock it onto a non-threatening orbit.
Another method, Johnson says, would be a “gravity tractor”. In this case, a spacecraft would rendezvous with the asteroid and hover above it for an extended length of time. The mutual pull of gravity between the spacecraft and the asteroid would gently tug the asteroid into a safer orbit.
The effect could be strengthened, Johnson says, if the spacecraft were to first pick up a boulder from the surface of the asteroid, thereby adding to its own mass.
A third approach would be to use a nuclear device. This doesn’t mean blowing it up, as in the movie Armageddon. Rather, the blast would be designed to heat the asteroid’s surface by enough that jets of matter would blow off into space, propelling it into a new orbit.
“Those are the techniques that current technology allows us,” Johnson says. “But part of the plan is to develop other techniques.”
To use them, however, the danger needs to be detected well in advance. “The minimum amount of time I would ever want to deal with to find an object would be at least 10 years before an impact,” Johnson says.
For large asteroids, this is feasible, especially as mapping and detection continues for those in the 140-metre class, but smaller ones are more capable of sneaking up on us.
And they can be dangerous. In 1908, for example, a 50-metre object blew up above the Tunguska region of Siberia, flattening trees over thousands of square kilometres. If the same event occurred over a large city, millions would die, the new report estimates.
And in 2013 a smaller asteroid blew up above Chelyabinsk, Russia, shattering windows and injuring 1000 people. “That was about a 20-metre-size object,” Johnson says.
In cases like that, Johnson explains, the goal is to provide warning. {%recommended 2047%}
“Even a short warning on the order of days or weeks gives us time to evacuate an area,” he says. In the case of an object like the one that blew up over Chelyabinsk, he adds, a warning could be issued to tell people to shelter in place.
Leviticus Lewis of the National Response Coordination Branch of the US Federal Emergency Management Agency adds that it’s also important to instruct emergency managers on what to do if their regions find themselves in the crosshairs of a Chelyabinsk or Tunguska type asteroid.
“Everyone in America knows what a hurricane is,” he says. But if there’s a threat of an asteroid impact, many people will have no idea what to do.
“We will be working to figure out what the questions are so that the national leadership and key executives can start thinking about what’s got to be the response.”
As an example of what can already be done, Johnson notes, a few months ago a two-to-three metre asteroid was detected about eight to nine hours before it came down in Botswana.
Initially, all that could be said was that it was going to come down somewhere in Africa or the Indian Ocean. But eventually, before it exploded like a second sun, asteroid trackers had successfully narrowed the impact zone to southern Africa.
