By Dr. Robert Thorson

Planet Earth just got a blast from the past. Mounting evidence indicates that a bona fide meteoroid created the new crater west of Lake Titicaca in Peru. Most convincing are the seismic shock, the scatter of iron-rich rock fragments and eyewitness reports of a bright fireball accompanied by a thunderous roar. Once again, humanity has been reminded that we are not in charge.

Larger forces are at work. Though trivial by geological standards, the meteoroid had a dramatic impact on the villagers of Carancas, near the Peru-Bolivia border. Hundreds were reported ill due to some combination of local changes in atmospheric chemistry and psychosomatic shock. I suspect that even the most ardent atheists among them were brought to their knees in humility.

I’m also betting that the local birthrate will rise. That’s what happened near Tunguska, Siberia, in 1908 when Earth experienced its largest otherworldly blast of recent history. The Tunguska event was caused an errant comet or meteoroid that exploded several miles above the surface with the energy of a thousand Hiroshimas.

The shock wave leveled trees for more than 800 square miles, which is roughly the size of a large metropolitan city and its surrounding suburbs. Boston. New York. Chicago. Seattle. Los Angeles. All would have been annihilated by a comparable explosion.

Imagine you’re in the batter’s box of a baseball diamond tossing a basketball into the air over home plate. Now imagine a pitching machine on the mound, occasionally firing ultra-fast high balls over the plate. Because the paths of the balls coincide, collisions are merely a matter of timing. A similar situation exists for baseball meteoroids whose orbits pass through that of basketball Earth’s. Collisions are rare, perhaps only once every few million years for asteroids one to two kilometers in diameter.

Few Americans realize that their risk of dying from an meteoroid impact isn’t trivial. In the worst case assumptions, it is lower than dying from a firearms accident, but higher than from a passenger aircraft crash. This risk is acknowledged by Section 321 of the NASA Authorization Act of 2005. This Public Law No. 109-155 authorizes the agency to identify threatening “near earth objects” and assess how to divert potential collisions. By 2020, they are mandated to “detect, track, catalogue, and characterize the physical characteristics” of at least 90 percent of NEOs 140 meters or more in diameter. This is much larger than the tiny object that struck Peru, and falls within the range of estimates for the Tunguska object.

Despite the planet-saving, suicidal heroics of Bruce Willis in the blockbuster “Armageddon,” there is only so much NASA can do to prevent asteroid disasters. The agency estimates that several hundred near earth objects are more than a kilometer in diameter, possibly too big to move effectively. They estimate that “30-80 percent of potentially hazardous NEOs are in orbits beyond the capability of current or planned launch systems.” For those reachable by spacecraft, the best diversion option is a nuclear explosion at some distance above the object.

Drilling into an asteroid or comet before detonating a nuclear device is riskier because the object might fragment out of control. Shooting high-velocity rockets into solid NEOs or nudging less firmly aggregated ones away with solar technologies are deemed less effective methods.

Approximately 40,000 tons of star stuff rains on the Earth each year. Most burns up before striking the ground. Fist- to suitcase-sized objects are informative curiosities. But larger objects pose a serious threat.

Yet at the same time, we owe our lives to their gravitational gatherings. Earth’s water-rich atmosphere was created by some combination of planetary melting from impact heat and the earlier arrival of volatile-rich comets. The measures of our lives — days, months and seasons — derive from the same large impact that gave us La Luna. The dinosaurs were smacked down by an object only 10 km in diameter, giving mammals the ecological room to flourish a few million years later.

We owe our lives to blasts from the past. Let us be thankful for that. And while we’re at it, let us be more respectful of forces larger than ourselves.