All of human life seemed on the brink of extinction on Feb. 15, at least according to several major news outlets when reporting of an incoming asteroid. In reality, Earth’s moon is 15 times closer to Earth than the asteroid was.
Asteroid 2002-PZ39 completed a close fly-by of Earth on Feb. 15, with headlines foreshadowing the beginning of the end. The asteroid, which contained its own small moon, proved to be no danger to the planet along its current trajectory. Other sources highlighted more asteroids nearing the Earth this week; however, none will impact it.
The data originates from NASA’s Jet Propulsion Lab’s Center for Near Earth Object Studies, according to Jaime Lombardi, professor of physics at Allegheny College. He pointed out that a larger celestial object passed closer to Earth last year.
“(Asteroid 2002-PZ39) would not have been mass extinction because it (only) has about 1/1000 the volume that you would need to have mass extinction,” Lombardi said. “It would need to be about 10 times larger in radius, so something that’s on the order of 10 kilometers, which is 6 miles across or larger — that could possibly cause mass extinction, but fortunately this was in radius about 1/10 that amount which means in volume it was about 1/1000 that amount.”
The 1-kilometer asteroid also had its own small moon. While it is not normal for an asteroid to have its own moon, Lombardi pointed out the quirks of such an oddity.
“A typical asteroid, even a large one, if you were to stand on its surface and jump off, you would float away because the gravity back down to the asteroid is not strong enough to pull you back,” Lombardi said. “When you take into account how weak the gravitational pulls are from these asteroids, it’s impressive that they can have moons, but occasionally if one’s close enough it can be stuck orbiting around it.”
Although asteroid 2002-PZ39 did not hit Earth, its strike would have resulted in cataclysmic events. Upon impact on land, it would have created a massive crater affecting 100,000 square miles. If it landed in the oceans, tsunamis would have eliminated coastal nations.
“If the object (from space) strikes in the water, then you get tsunamis,” Lombardi said. “That in a sense can be even more devastating because depending on where it hits, you could wipe out coastlines, and if you think of places like Bangladesh, which have millions of people all within just a few meters of sea level, then something like a tsunami could have truly devastating consequences.”
Scientists spend decades calculating and observing outer space to accurately chart the paths of asteroids. Lombardi credits Newtonian mechanics and the equation, f=ma, as being the main calculator.
“If you know those forces which we can calculate, you can calculate the acceleration of the asteroid, and the acceleration tells you how its velocity changes, and its velocity tells you how its position changes,” Lombardi said. “What you basically do is you calculate the forces and you update the position of the asteroid and then you recalculate the forces and you update the position of the asteroid, and you just keep on doing that forever and ever ad infinitum.”
The first major asteroid to be tracked to collide with Earth was Apophis, which is set to fly by on Friday, April 13, 2029. It was the only celestial object to be given a non zero score on the Torino Impact Hazard Scale, a scale ranging from 0 to 10 which measures out severity of collisions.
“At the time, the calculations of its trajectory put it at something like a 1/60 chance that it would hit the Earth, and so they knew even (when Apophis was discovered in 2004), when there was the maximum likelihood that it could hit the Earth, that it would miss in 2029,” Lombardi said. “But if it goes through just the wrong place in what’s called a gravitational keyhole, then its orbit would … come around (seven years later), so then in 2036 it hit.”
Over time, Apophis was reexamined and reduced back to a zero on the Torino Scale after it was discovered that it would pass by the planet. However, there are objects in the solar system with the capability of impacting Earth.
In response to a threat of collision, scientists have developed ways to change the course of the asteroid. One of those is the use of “gravitational tugboats,” which get placed next to the object’s path and change its gravity, according to Lombardi.
“If you can launch some object up and put it next to the asteroid, then you can just gravitationally tug on it from this spacecraft, or whatever you’ve placed next to it, and that gravitational tug could change its directory ever so slightly, but enough that it misses the Earth and flies by rather than strikes it,” Lombardi said.
He pointed out that years of advanced notice would be required to pull off that mission.
Another idea brought up by scientists is the launch of nuclear warheads to break up the asteroid, blowing it up and spreading its pieces.
“If it’s already headed at the Earth and it’s going to strike tomorrow and you blow it up, now rather than one big object you have many small objects that are going to strike the Earth,” Lombardi said. “That would probably be better because you would burn up more stuff in the atmosphere before it struck, but it still wouldn’t save you necessarily from all of the damage being done.”
Lombardi said that although asteroids are dangerous, comets remain a greater threat because of how comets are made compared to asteroids and the fact that they come from outside of the solar system.
“Comets are not rocky,” Lombardi said. “They’re little ice balls but they can be big as well, many kilometers across the nucleus if you’re unlucky. Halley’s Comet, for example, comes by and swings around the Earth every approximately 75 years or so. Fortunately, Halley’s Comet is not on an intersect course with the Earth — it’s not ever going to strike the Earth — but there could be some other comet that’s gravitationally scattered in the other parts of the solar system, and if that comes in and you’re unlucky and it’s headed towards the Earth, you have very little advanced notice of this and so humanity would have to react quickly.”
Although the likelihood of an impact of a celestial object is rare, the effects on an impact will last for centuries. Lombardi pointed out that remains of the object that caused the dinosaur extinction still has a crater in the Yucatán Peninsula. He also noted that the dinosaurs did not go extinct directly after the object collided with Earth, but rather that a cloud of debris in the atmosphere caused a global climate change.
“They didn’t die out all on the day that the impact occurred, it probably took on the order of 10,000 years or so for them to die off as they were fighting these great changes in the climate,” Lombardi said. “That’s why (with) these large objects, you need something that’s 6 miles across or wider because then if the debris from that impact gets up above the atmosphere, that’s when you can really have these devastating consequences.”
Although some may have jumped the gun on a possible annihilation of all life on Earth, the danger of an extinction level event eliminating all life on the planet remains as foreboding as ever.