It’s never too early to plan ahead.
“There’s no question that asteroids strike the earth and can create great damage,” says Jay Apt, an astronaut who has flown four space shuttle missions, two as shift commander, and who teaches engineering at Carnegie Mellon. “These strikes don’t necessarily plunge the Earth into winter for many years, though it is something to take very seriously.”
“But,” he continues, “once you see an asteroid coming this way, the question is what to do about it.”
Scientists have debated that at least since the Tunguska Impact of 1908, when an asteroid exploded over Siberia and, with the power of multiple atomic bombs, took out 80 million trees over a frozen expanse of 830 square miles. Astronomers have since counted 1,097,558 of the “rocky, airless remnants,” as NASA puts it, in our solar system. Sometimes, one of them can enter Earth’s orbit, the prospect of which fuels the imaginations of science fiction writers and the nightmares of astronomers alike.
The American science fiction writer Larry Niven once said, “The dinosaurs became extinct because they didn’t have a space program.”
And now we have a tentative answer to the threat of an asteroid colliding, to cataclysmic effect, with our planet: NASA’s Double Asteroid Redirection Test, or DART.
Developed by a team of scientists from the Johns Hopkins University Applied Physics Laboratory and NASA’s Planetary Defense Coordination Office, DART is an unmanned, remotely controlled astronomical suicide mission designed to nudge an asteroid that is half a mile in diameter out of its orbit. Doomsayers take note: This is only a test. The asteroid in question, Didymos — Greek for “twin,” and so named because it was discovered to be paired with its own small moon — is not actually on a collision course with Earth.
Sometime between Thanksgiving week (perhaps as soon as the evening of Nov. 23) and February 2022, the team behind DART will launch it from Vandenberg Space Force Base in California on a SpaceX Falcon 9 rocket. The spacecraft will, if all goes according to plan, travel 6.8 million miles to reach and collide with Didymos’s moonlet, Dimorphos, which is 525 feet in diameter.
DART will also ferry a shoebox-sized spacecraft contributed by the Italian Space Agency. Several days before DART’s impact with Dimorphos, that little craft, the LICIACube (Light Italian CubeSat for Imaging of Asteroids), will separate from DART to capture images of the impact.
Success will destroy DART but also provide data on how the collision alters the speed of the moon around its larger companion. The goal: to learn how to speed up or slow down an asteroid’s transit so that it can be done again if and when the asteroid in question is headed for Earth.
Only a little tap from DART will make an enormous difference.
“If you know an asteroid’s orbit for a long time and have advance warning, and if you think it will hit the Earth, even a tiny nudge far away will change the trajectory of the asteroid and save the Earth,” says Michael J. Neufeld, senior curator of the National Air and Space Museum.
But what if DART is a dud, or what if the technology doesn’t work quite right? Are we simply to be the victims of, to summon Robert Frost’s 1920 poem of the same name, fire and ice?
“We have other tools,” says Thomas D. Jones, a veteran of four space shuttle flights who is chairman of the committee on Near-Earth Objects of the Association of Space Explorers. “We can ‘park’ nearby and tug on the object through gravitational pulls. We can use a nuclear explosive device. And there is an exotic idea of using a solar-powered laser pulse to hit the asteroid repeatedly, creating a puff of gas that will vaporize a piece of the surface and propel the asteroid like a rocket. But the physics of DART are simple: We just run into the object the way we have automobile crashes on Earth.’’
One way or another, moving asteroids out of the way of Earth is a preoccupation of astronauts such as Jones, whose committee believes the “chances are 100 percent that our planet will be struck again by a large Near-Earth Object” and that there are as many as 1,000 “threats to human civilization” traveling near the planet.
Plus there is this challenge: Winning support — technical, economic, political — for a global mobilization against an asteroid careering toward Earth. As Kelly Fast, manager of NASA’s Near-Earth Object Observation Program, put it during an Association of Space Explorers seminar last week, “Planetary defense is a team sport.”
Asteroids were first discovered on New Year’s Day 1801, in the very first hours of the 19th century. In the decades that followed that discovery, science fiction writers speculated on how earthlings might redirect asteroids, perhaps to use them for resources, to produce rocket fuel, or even to employ them for settlement. The real push to create a planetary defense came in the past half-century. “There’s a growing sense we need to track these things and see if we can do anything about diverting them,” says Andrew Rivkin, a Johns Hopkins planetary researcher involved in the DART project.
Asteroid anxiety, in other words, is real.
So is confusion about what, exactly, happens when an asteroid reaches Earth’s atmosphere. In 2017, a team of researchers determined that the cracks and pores in an asteroid’s surface let in high-pressure air that creates massive internal pressure. Most asteroids effectively explode from within before actually hitting Earth’s surface.
This happened 26 times in the first 14 years of the 21st century. Sensors installed around Earth because of the Nuclear Test Ban Treaty Organization, which monitors the infrasound signature of nuclear detonations, identified the nuclear-strength asteroid explosions, most of which occurred over oceans.
On Feb. 15, 2013, however, a 66-foot-long asteroid traveling at 40,000 miles per hour exploded about 20 miles above Chelyabinsk, Russia. With a force 30 times that of the Hiroshima bomb, it damaged thousands of buildings across six cities and injured 1,500 people. Scientists widely believe that the destructive potential of an asteroid or other near-Earth object could exceed regional catastrophe and be global in scale.
Imagine, then, what an asteroid with a diameter of half a mile, like Didymos, could do.
‘A little safer’
The modern pioneers of asteroid deflection were scientists with the European Space Agency (ESA) who crafted a double-spacecraft plan they called Don Quijote two decades ago. The mission would have deployed one spacecraft, Hidalgo, to crash into an asteroid, and a second, Sancho, to observe the change in its momentum.
Facing a funding shortfall, Don Quijote didn’t make it out of initial studies, which led to a 2010 report by the National Research Council in the United States, ominously titled “Defending Planet Earth.” It urged “an experimental test of a kinetic impactor along with a characterization, monitoring and verification system, such as the Don Quijote mission that was previously considered but not funded by the European Space Agency.”
In 2018, ESA produced Hera, a smaller spacecraft that is scheduled to follow DART into deep space after five years to study the crater that DART produces.
DART’s mission is no easy undertaking. While something of its size would cause a huge explosion in Earth’s atmosphere, Dimorphos is actually quite small as celestial bodies go. DART will travel at approximately 4 miles a second, and in the spacecraft’s final four hours before collision, scientists on the ground will yield DART’s steering to autonomous onboard computers that will have a greater-than-human-guided chance of smashing DART into the rock, thus pushing the asteroid off course.
The long-term effect of such efforts, Hopkins’s Rivkin says, “is to make the planet a little safer.”
But not entirely safe. There are other threats out there in space, like comets hurtling toward Earth at high velocity. They can come from completely unexpected directions, and we can have no advance warning of their arrival. But that’s for another day, and another essay.
David Shribman, previously the Globe’s Washington bureau chief, is executive editor emeritus of the Pittsburgh Post-Gazette and a nationally syndicated columnist.