Five years ago, on an otherwise normal Friday morning in Chelyabinsk, Russia, a six-story meteor—seemingly out of nowhere—burst across the clear blue sky as commuters were making their way to work. This surreal fireball—hurtling toward the Earth at 42,000 miles per hour and burning brighter than the sun—was caught on at least a dozen dashboard cameras before it exploded 19 miles above the city. (Nearly every car in Russia is outfitted with a dashboard camera, with footage typically used to settle traffic disputes.)
The blast from the largest asteroid to pierce the Earth’s atmosphere since the 1908 Tungaska event, which flattened some 800 square miles of Siberian forest, damaged 7,200 buildings in six cities, shattering windows and injuring more than 1,600 people.
Suffice to say, the episode was an effective reminder that about two-dozen meteors pop through the Earth’s atmosphere every year, including on average at least one the size of an automobile. It also proved a wake-up call for Congress, which began holding hearings about the threat to U.S. public safety. After all, the next 7,000-ton, flaming rock could just as likely land on I-95 as a Siberian forest.
NASA eventually announced the creation of the Planetary Defense Coordination Office. The big question they needed to figure out, of course, was how exactly do you divert a rogue asteroid from an orbital collision with Earth? How do you design, model, and fly something into a speeding space rock and then measure the change in its trajectory?
The answer came to Andy Cheng, of the Johns Hopkins Applied Physics Laboratory in Howard County, in his basement during his morning calisthenics routine. Cheng realized the simplest approach was to crash a spacecraft into the smaller of a twin pair of asteroids—whose orbits are linked—and then measure the change in the orbit of the smaller asteroid against its larger twin. Up until that point, leading planetary defense scientists, including those at the European Space Agency, assumed they needed to build two spacecrafts—a prohibitive cost—one to smash into the asteroid and a second to document the change in its orbit. Measuring the changes in the asteroid’s rotation and spin against its twin, however, scientists could manage from their telescopes.
“It was a light bulb moment,” Cheng says with a laugh. “I was at home, stretching, in my normal routine before work, and I thought, ‘I know how to do it.’”
The chief scientist of the Space Department at the Applied Physics Laboratory, Cheng jokes he should be retired by now. He well remembers the year he moved to Baltimore (he currently lives in Potomac) to take a job at JHU’s Applied Physics Lab because it’s the same year the Orioles last won a World Series—1983. Instead, the 66-year-old grandfather is the co-lead investigator on the first-ever mission, nicknamed DART (Double Asteroid Redirection Test), to demonstrate an asteroid deflection in real time, in real space, for planetary defense purposes.
“I’m just having too much fun to quit."
Given the way the threat of asteroids has permeated pop culture, namely end-of-the-world movies such as Deep Impact and Armageddon, it’s easy to forget that the study of asteroids is really new science. We put a man on the moon a decade before the first scientists theorized a giant asteroid had caused the mysterious extinction of the dinosaurs (not to mention three-quarters of all living species) 66 million years ago. That asteroid, with a diameter half the length of Manhattan, dented the Yucatan Peninsula with such force that it’s estimated 330-foot waves crested the shores of what are now Texas and Florida. More significantly, it ignited such an explosion on impact that the ensuing billow of dust, sulfur, and carbon dioxide blocked out the sun’s rays for years, driving down global temperatures and setting off a chain reaction of ecosystem catastrophes.
Closer to home, it wasn’t until 1983 that scientists discovered the first hint of the 53-mile impact crater buried beneath the Chesapeake Bay—left by the crash of an asteroid more than a mile in diameter.
“You know the saying: ‘The dinosaurs became extinct because they didn't have a space program,’” says NASA’s Tom Statler, quoting science fiction author Larry Niven and only half-kidding. “Only in hindsight does it seem obvious that all these [previously believed volcanic] craters were the result of asteroids crashing into planets.” All told, Statler adds, about 100 tons of extraterrestrial matter falls onto the Earth every day, mostly in the form of harmless dust, but also the occasional small meteorite.
For the record, the asteroid that exploded over Chelyabinsk is considered “small” by NASA’s near-Earth asteroid tracking standards. As was the fiery 26-pound rock that smashed through the trunk of 18-year-old Michelle Knapp’s Chevrolet Malibu while it was parked in her family’s Peekskill, New York, driveway in 1992, and the 8.5-pound space rock that crashed through an Alabama farmhouse in 1954, injuring Ann Hodges while she was napping on her sofa. Remarkably, there are no known human casualties from asteroids in recorded history, although a dog in a village outside Cairo, Egypt, was reportedly killed by a falling fragment in 1911. (Intercepting these small meteorites isn’t on the table at NASA or the Applied Physics Lab. Planetary defense scientists have their hands full tracking the thousands of near-Earth asteroids five times the size of the most recent Russian asteroid or larger.)
Roughly 95 percent, or about 15,000, of the large near-Earth asteroids have been located, says Statler, who serves as the NASA program scientist overseeing the DART mission. But until Cheng’s breakthrough idea, redirection was considered extremely difficult and borderline unverifiable.
“I wish I had thought of it,” Statler says.
As the timeline stands, the APL-built DART spacecraft will launch in June 2021 and impact Didymoon—the smaller twin to the asteroid Didymos (Greek for twin)—6.8 million miles from Earth on Oct. 7, 2022.
“Each asteroid has been to different places. Each has its own history.”
This summer, the White House released the administration’s 2019 budget request of $150 million for planetary defense, including $90 million for the DART mission. The White House also outlined goals to address the small but “high-consequence” threat posed by near-Earth objects, further developing technologies for deflecting or disrupting potential collisions (including a nuclear missile in the worst case scenario).
Meanwhile, notes Nancy Chabot, an APL project scientist, amateur astronomers will be able to track the DART project’s effect on the orbits of the Didymos asteroids when they are close to Earth. “We welcome anyone with a telescope to help,” she says of what will be the years-long observations of the twin rocks.
Most asteroids that stray near Earth—the Didymos pair, the Chelyabinsk rock, or others—are fragments of larger asteroids, numbering in the millions, from an enormous asteroid belt between the orbits of Mars and Jupiter. Some are rich in precious metals—asteroid mining is predicted as a thing of the future. Some asteroids are actually blown out comets with all the ice gone and just the rocky minerals left behind. Some have eccentric orbits. “Each asteroid has been to different places,” says Columbia resident Andy Rivkin, co-lead investigator with Cheng on the DART mission. "Each one has its own history.”
Rivkin adds that in recent years it has been theorized that most of the water on Earth may have come from asteroids and not comets.
The DART mission is not the only current high-profile project out of the Hopkins lab, which employs more than 6,000 people on its sprawling 20-building, 453-acre campus. The APL designed, built, and operates the recently launched $1.5 billion Parker Solar Probe, which will fly seven times closer to the sun than any previous mission. That spacecraft will explore, among other sun properties, the powerful solar winds that affect Earth, occasionally derailing satellites and GPS systems.
Other recent missions based at the Laurel facility include MESSENGER, the first spacecraft to orbit Mercury, and the New Horizons mission to Pluto. And yes, Pluto is still a planet, although it is now considered a dwarf planet, of which there are many in our solar system. “The question everyone asks at a cocktail party when they find out you're a planetary astronomer,” says Rivkin.
Meanwhile, APL planetary geophysicist Olivier Barnouin, who worked on the MESSENGER and New Horizons projects, helped write the proposal for another ongoing high-profile project overseen by NASA’s Goddard Flight Center in Greenbelt. The OSIRIS-REx project is the first U.S. mission designed to bring back an asteroid sample, from a primitive asteroid named Bennu, which scientists hope will reveal new information about the formation of the solar system.
“[With the OSIRIS-REx project], we are talking about being able to answer what are religious-type questions in the scientific community,” says Barnouin. “One hypothesis people go for is that in reality we are all aliens—that almost everything that is needed for life on Earth came from outer space.”
An asteroid estimated to be 4.5 billion years old with a diameter of the Empire State Building, Bennu, named after a mythological Egyptian bird, takes a close orbit to the Earth every six years. It is also noteworthy because it’s one of the large near-Earth asteroids with the best odds of impacting Earth, albeit sometime late next century. Granted, it’s a slim shot—an estimated 1 in 2,700 chance—but that’s still twice the probability of the average little leaguer making it to the big leagues. It’s also better odds than getting struck by lightning, which kills a couple dozen people in the U.S. each year.
Space, which is sometimes depicted as a great void and at other times as an asteroid and comet superhighway, is actually neither.
“Space is big,” says Rivkin. “But if you wait around long enough, something will come by.”