Planetary defense experts use infamous asteroid Apophis to practice spotting dangerous space rocks

March 2, 2021 by No Comments

Apophis definitely won’t hit Earth this month, but scientists are pretending it might.

Earth’s most recent brush with asteroid danger was eight years ago, when a space rock the size of a six-story building came seemingly out of nowhere, injuring 1,200 people when it exploded over Chelyabinsk, Russia.

Now, scientists are using this month’s flyby of the infamous asteroid Apophis to test their responses to potentially hazardous space rocks, honing the fine art of planetary defense. Planetary defense focuses on identifying asteroids and comets that hang out around Earth, mapping their precise paths and seeing how their orbits compare with Earth’s.

If an orbital model shows that an asteroid and Earth are due to reach the same place at the same time, things get serious, particularly when the space rock is large. That’s the sort of scenario that ended the dinosaurs’ reign, after all. But planetary defense isn’t hopeless: if humans identify a dangerous asteroid long enough before impact, we could theoretically do something to divert it.

Successfully preventing damage from an asteroid impact will depend on spotting the threat in time, which takes practice. But although scientists have identified more than 25,000 near-Earth asteroids to date, the majority are too small to cause much worry. So while there are plenty of asteroids rattling around Earth’s orbit, most aren’t big enough or close enough to trigger realistic existential angst.

Apophis came to its fame because it isn’t like most of these near-Earth space rocks. When scientists discovered it in 2004, it stood out right away. First, it is relatively large — more than 1,000 feet (300 meters) wide, around the height of the Eiffel Tower, according to NASA. And models based on early observations suggested a nearly 3% chance Apophis would collide with Earth on April 13, 2029.

More precise observations soon put the fear of impact that year to rest, but the early concern surrounding the asteroid prompted its name, which references an Egyptian “demon serpent who personified evil and chaos,” as NASA put it. Right now, scientists are confident that Apophis is no threat to Earth for at least a few decades. But the space rock will still come visiting next month, offering scientists valuable opportunities to get a close look at a relatively large asteroid.

And, with a little imagination, these flybys can also serve as planetary defense rehearsals.

“The goal is to basically wrangle all the scientists from around the world, kind of the coalition of the willing,” Vishnu Reddy, a planetary defense expert at the University of Arizona who is coordinating the project, told “Then we go on this months-long campaign, trying to observe this object.”

Apophis will fly past Earth on March 5. The asteroid will remain about one-tenth the average Earth-sun distance away — a downright mundane flyby compared to the 2029 event, when Apophis will pass by at about the altitude at which particularly high satellites orbit.

To mark this year’s flyby, the International Asteroid Warning Network instituted its third such campaign. Previously, scientists have practiced on an asteroid called 2012 TC4 and on 1999 KW4, which is a pair of rocks circling each other. For Apophis, about 40 scientists from 13 different countries have signed on. These observers are pretending that Apophis has never been seen before, which means they are starting from scratch in terms of evaluating how much danger the asteroid poses to Earth.

“It’s not a scientific goal,” Reddy said. “The goal is to get new observations as if we don’t know anything about this object and try and see where in the process we need to improve efficiency and also identify the human factor. Anybody dealing with scientists knows that it’s like herding cats, and when you do that on an international scale, there’s part diplomacy, part science, and part planetary defense.”

Reddy said that the coincidence of the Apophis flyby occurring during the continuing COVID-19 pandemic offered an opportunity to understand how resilient the asteroid detection system is. At this point, most telescopes are managing to continue operating, although he said the pandemic likely would have interfered much more had the flyby occurred a year earlier, when institutions were still scrambling to respond.

“There’s a reasonable amount of redundancy in planetary defense,” he said. “Even if one telescope goes down or we lose a certain thing, it’s not like the whole community goes down, to some extent.”