A very strange series of memos arrived at the White House during the fall of 2017, detailing a would-be nightmare scenario: an asteroid apparently on track to hit Earth. But those memos were covered in bright red warnings noting that they were just part of a drill; humanity didn't have any more reasons than normal to fear civilization's end.
The memos were part of a surreal, sophisticated drill that let NASA and the scientific community practice for the existential threat of an asteroid that seems to be on track to hit Earth — all based on a real asteroid. And now, the team involved in the drill has published a final set of findings about how the project went and what humans can do to be better prepared for this potential apocalypse scenario.
"The most important thing was [that] it was the first time we actually tested the whole system, including notification to the White House," Vishnu Reddy, a planetary defense expert at the University of Arizona and a co-author on the new paper, told Space.com last month at the annual Lunar and Planetary Science Conference held in The Woodlands, Texas. "It was a really fantastic experience for us to test with a real asteroid."
Early in 2017, scientists decided they wanted to conduct such a drill. So they went looking for an asteroid, one that wasn't really a risk but that would come close enough to produce realistic data about how an actual risk could play out. That would allow planetary defense specialists, who exclusively study the threat of asteroid impacts, to test their observation, evaluation and response procedures.
A space rock known as 2012 TC4 fit the bill. During this object's initial detection in 2012, observations of its path through the solar system suggested that it would make a close — but not dangerously close — approach to Earth in October 2017, although researchers weren't positive exactly what track it would take.
That's how the asteroid earned its role as guinea pig for the end of the world as we know it.
"We knew it wasn't a threat … we wanted it to be an exercise, but TC4 was a good candidate," Michael Kelley, a NASA scientist in the planetary defense program and co-author on the overview paper, said during a presentation at the same conference. "It was an asteroid with a slightly uncertain orbit that was in the time frame we were looking for to conduct this exercise. We knew it was out there. We knew roughly where to look in the sky, but we didn't know exactly where to point the telescopes, so we would have to search a little bit to try to find it."
That search began in July 2017, when a team using the Very Large Telescope in Chile began trying to spot TC4. They latched on for good in August, when they had expected they would be able to. A different telescope, Pan-STARRS in Hawaii, also proved separately that, had scientists not possessed the 2012 data, they still would have spotted the asteroid about two weeks before the 2017 closest approach.
As TC4 hurtled closer, scientists turned telescopes around the globe toward the object. First, they looked to track its path. Observers and orbital-trajectory specialists worked together to update their expectations of where precisely the rock would travel, one of the key responsibilities of planetary defense. As that picture developed, the team brought the data to government officials to talk through how the situation would be handled in real life.
The good news is you never heard about a large asteroid hitting Earth in the fall of 2017. The more complicated finding is that there was a time when the team's calculations suggested that this was a real possibility, Kelley said. Briefly, on Sept. 24 of that year, the calculations gave TC4 a 1 in 180 chance of hitting Earth. "This is well below the threshold to trip all the triggers for an emergency situation," Kelley said.
Fortunately, within just a few days, that sliver of a chance had evaporated. The uncertainty makes for a risky situation nevertheless, he added, since the team never wants to act rashly and cause a panic. But someone not following the entire process could have taken that one day's data out of context, intentionally or not.
"You have to be very, very careful when you have a lot of measurements coming in and you're waiting to see what fits the pattern and what does not fit the pattern," Kelley said. "You can get to a point where you are drawing the wrong conclusion if you stop at a certain point or if you just take a snapshot image."
By the end of the exercise, the team had completely eliminated any probability of impact from TC4 in the foreseeable future.
But scientists weren't content with simply predicting the asteroid's path; they also wanted to gather as much data as possible about the rock itself. In particular, they investigated how it dimmed and brightened as it spun in space. In the context of a potential impactor, this information is not just scientifically interesting. More than that, details about an asteroid's rotation and composition can shape the potential disaster, affecting how much of the initial mass makes it through Earth's destructive atmosphere.
Here, too, things got a little dicey. The team had lined up a range of facilities they wanted to use in advance, but fate intervened. Scientists had wanted to use the massive radio dish at Arecibo in Puerto Rico to bounce light waves off the asteroid's surface and see how they bounced back. But Hurricane Maria devastated the island just a couple weeks before the asteroid's closest approach, and the telescope wasn't ready to help. Scientists had to scramble to rope in two other radio telescopes, Goldstone and Green Bank, to make up for Arecibo's absence.
And the team had wanted to use NASA's Infrared Telescope Facility in Hawaii to better understand the object's composition. The telescope had a three-night window to catch TC4. It observed the asteroid on the first night and was put to another task on the second. On the third night, the power went out.
"It turns out that somebody cut a tree down and the tree fell on the power line," Reddy said. "And so the fate of the world will end up in [the hands of] some person with an ax in the hand trying to chop a tree in the evening."
There's no reason to suspect that the same sorts of mundane issues would patiently wait for a real threat to pass. "There are real-world problems that can crop up even in an emergency situation," Kelley said. "Bad timing is always there."
Despite the challenges during observations, scientists are pretty satisfied with what they were able to learn about TC4. It seems to be very bright, about 33 feet (10 meters) across, with a jagged, uneven surface. "This may be a fragment of a very bright, white rock in space," Kelley said. It seems to resemble an unusual type of meteorite — a kind that makes up just 1% of the space rocks we have here on Earth — called aubrites.
Now that the results of the TC4 drill are published, the team is ready to apply the lessons learned during the exercise to a new drill. That team has selected a different asteroid, again based on the object's orbital convenience. "We can't schedule the asteroid[s]. We kind of have to wait for them to cooperate," Kelley said.
This drill will be of a smaller scale than the TC4 one was, aiming only to learn as much as possible about the space rock itself — even though scientists already have a good sense of what it is.
"We know a lot, but we're pretending as if we don't know," Reddy said. "Imagine if this asteroid is going to hit us, say, 15, 20 years from now and this is the last, best flyby when we can characterize it to know what to do in the next 15, 20 years before impact. What can we learn?"
This kind of preparation is not just about learning about distant space rocks sailing through the solar system. It also means learning about deeply terrestrial, deeply human factors, like how to be ready if someone cuts the wrong tree down on the wrong day.
"This exercise was actually a good lesson in the reality of trying to do this as well, in a practical sense," Kelley said. "Real-world events affected the campaign, but we dealt with them and worked through it." And as a result, humans should be better prepared for the next close approach.
"Fortunately, the fate of the Earth wasn't riding on this one, so we're OK," he said.
The project is described in a paper published in March in the journal Icarus.
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