Last week, humans around the world looked up to see dazzling streaks of light fall across the sky during the annual Geminid meteor shower. For most, such celestial shows offer a beautiful and sobering reminder of our tiny place on Earth amidst the magnitude of our galaxy. For Joseph Nuth, an astrophysicist at NASA Goddard Space Flight Center in Maryland, they portend a bleaker possibility.
“Each meteor shower is a potential comet-Earth collision that just didn’t occur because the Earth wasn’t in the right place, or in this case, the wrong place,” Nuth put it bluntly during a presentation at this year's American Geophysical Union meeting in San Francisco last week. Fortunately, he has a plan: Nuth is part of an international team of researchers working to protect Earth from getting struck by potentially devastating comets and asteroids.
The threats posed by so-called Near Earth Objects (NEO) range from localized injuries—as in the 2013 Chelyabinsk meteor impact in Russia that injured 1,500 people—to mass extinctions like the one that wiped out the dinosaurs. Yet these threats also present an unusual opportunity for nations to band together to protect all Earthlings from imminent danger. After all, an asteroid impact could potentially be a global disaster, says Brent Barbee, an aerospace engineer with NASA Goddard Space Flight Center.
“Asteroids certainly don’t discriminate between nations, and an impact can occur on anyone’s territory,” says Barbee.
There’s another factor that makes the threat of asteroid impacts a unique opportunity for global unity. Unlike some more localized natural hazards, like volcanic eruptions and tsunamis, these kinds of impacts are theoretically preventable. “It’s the only natural disaster that we really have the ability to—at least in principle—prevent,” says Barbee. “That creates a certain type of international collaboration that is very unique.”
Scientists didn’t fully appreciate the devastating potential of comets and asteroids hitting Earth until the 1980s, when physicist Louis Alvarez and his son Walter Alvarez first suggested that an impact caused the extinction of dinosaurs. Since then, advancements in space observing technology have revealed more than 700,000 asteroids in our solar system—a feat accomplished through the collaboration of thousands of scientists around the world, according to Michael Busch, a researcher at the SETI Institute in California.
Telescopes in Australia and Chile, for example, have played an important role in identifying asteroids. We now know there are at least 15,000 within 50 million kilometers of the Earth’s orbit, a distance that officially qualifies them as potentially threatening Near Earth Objects, Busch says. Meanwhile, researchers in Japan, China, the European Union and the U.S. have played large roles in developing technology to better characterize these asteroids. Japan, for example, launched an asteroid explorer called Hayabusa2 in 2014, which aims to collect material from an asteroid in 2018; if all goes well, it will return to Earth in 2020.
But knowing that objects are out there and collecting information from them is not the same as being able to protect Earth from impacts, as Nuth warned last week. The next step is establishing an action plan to intercept an object heading toward Earth. The success of this mission requires that NASA work with other large space agencies like the European Space Agency (ESA) to build and launch intercepting spacecraft before the object hits Earth, Nuth explained.
Building and launching a high-reliability spacecraft can take five years from start to finish. Depending on the situation, that may be more time than we have to spend. Nuth cited the recent case of the Siding Spring comet, which came unnervingly close to Earth in 2014—only 22 months after researchers detected it for the first time at the Siding Spring Observatory in Australia. “It is imperative that we reduce that reaction time,” Nuth says.
To do that, Nuth proposes that NASA build spacecraft to observe and intercept objects, and store these spacecraft away until an object poses an imminent threat. Even then, the timeline of launching would depend on budget allocations from Congress and on Earth’s position in its orbit around the sun relative to the incoming object, Busch says. But having the equipment ready would shave off years in preparation time, Nuth argues.
The type of interceptor deployed would depend on the size of the incoming object, Nuth’s colleagues explained during a press conference at the meeting last week. For smaller objects, you might deploy something akin to a cannonball. But a much larger object could require a nuclear explosive device, says Catherine Plesko, a researcher at Los Alamos National Laboratory.
“Nuclear is the way to get the largest amount of energy out to the object in the smallest possible container,” says Plesko.
In both cases, the goal would be to push the object off course, as opposed to destroying it and sending potentially hazardous shrapnel toward Earth, Plesko says.
Such interceptors would only be used on the most pressing threats to Earth, such as objects aimed at high population areas on land or in near coastal areas. Open ocean impacts worry the researchers less because they very rarely cause tsunamis, although these can send water vapor into the stratosphere where it could have long-lasting climate impacts.
While astronomers can spot asteroids centuries or even millennia before they hit Earth, comets are more difficult to prepare for because they travel from much farther away and up to four times faster than asteroids, leaving less time to react, says Mark Boslough, a physicist at Sandia National Laboratories in New Mexico. “Every once in a while one falls in, and we have a year or less between when we discover it and when we need to act,” Boslough said.
This is where Nuth’s plan for squirreling away a spacecraft would come into play.
But not all astronomers are on board with this idea. Michael Busch at the SETI Institute argues that storing away spacecraft could allow someone with ill intentions to direct an asteroid that wouldn’t otherwise hit Earth on a path toward the planet. “That can be done, if you are suitably evil,” says Busch, pointing out that late astronomers Carl Sagan and Steven Ostro presented this view in a paper in the mid 1990s.
Still, Busch is a firm advocate of NASA funding Near Earth Object research—the future of which remains unclear with the next presidential administration. The Trump administration has proposed slashing funding for NASA’s Earth Science department, but has expressed a commitment to deep space exploration, which might include research on Near Earth Objects. While funding for this research has been steady and has even increased in recent years since the Chelyabinsk event, the future of these NASA efforts has yet to be determined, Busch says.
NASA is currently pursuing funding for a project called the Double Asteroid Redirection Test (DART), in which it would test the cannonball iteration of intercepting an oncoming asteroid. But the ability of DART to move forward is contingent on NASA’s budget, which has not been finalized for the coming year. “Those projects are having trouble going forward because we don’t currently have a budget for NASA for next year,” Busch says.
In May, the International Academy of Astronautics will meet in Tokyo for a planetary defense conference to discuss next steps toward protecting the planet impacts. In the meantime, Busch hopes that NASA funding will go through so that the U.S. can work with other countries around the world on this universally—or at least globally—important issue. After all, he says, “the asteroid does not care about any of our borders before it hits the ground."