Early Friday afternoon (2:24 p.m. EST), planet Earth will be buzzed by an asteroid some 150 feet wide, identified as 2012 DA14, as it intersects Earth’s orbit just 17,500 miles above our heads.
According to NASA, this is the closest documented encounter of an asteroid this large (excluding ones which actually smashed into the Earth). While this might not seem at first even a close miss, on the cosmic scale of the solar system, it certainly qualifies as a very close call.
Only last December a somewhat smaller asteroid, XE54, passed within about 140,000 miles of Earth, and was about as close to crashing into Earth as an asteroid can without actually doing so.
(Note: For perspective, a relatively simple calculation shows that DA14’s closest approach corresponds proportionately to two commercial aircraft approaching to within about 150 feet of one another. That is far below FAA requirements for the minimum safe horizontal separation between airliners - 3 to 10 miles. There is little doubt that coming as close as 150 feet, which is less than the wingspan of even most mid-sized commercial passenger planes, is as close one can imagine without having a disastrous mid-air collision.)
Several recent asteroids have come closer than DA14 but were much smaller (tens of feet in size). And, when it comes to the consequences of an Earth-asteroid collision, size really matters.
The smallest asteroids (better described as large rocks) to threaten Earth most likely would burn up in the atmosphere creating eye-opening fireballs racing across the sky, possibly with some fragments (referred to as meteorites) reaching the ground. (Note, by comparison, the “shooting stars” seen annually in association with meteor showers are typically pebble sized).
An asteroid the size of DA14 is capable of blasting a crater - with the equivalent of hundreds of Hiroshima atomic bombs – like the one mile wide hole known as Meteor Crater blasted into the ground 50 thousand years ago in Arizona.
Just 105 years ago (June, 1908) a 300 foot asteroid (or comet comprised of mostly water ice rather than hard rock) exploded over the Tunguska River in Siberia with more power than anything before or since (including thermo-nuclear hydrogen bombs) in recorded history. Thousands of square miles of territory were devastated, but the only victims were trees and wild life.
An equivalent strike today near a metropolitan area would obviously cause tremendous damage and take a terrible toll on life and societal infrastructure. However, it’s much more likely that the asteroid would either produce a big splash (and possible tidal waves) somewhere over the vastness of earth’s oceans, or create a humongous bang (and possible earthquakes) over some relatively large and sparsely populated land mass. In either case, though, the event would not wipe out humanity.
Scientists believe that any space rock larger than about 1 kilometer (.62 mile) across could cause a global catastrophe. The asteroid which led to the mass extinction of dinosaurs 75 million years ago was about 10 kilometers (6.2 miles) wide.
“Extinction event” asteroid collisions appear highly improbable (but possible) on time scales less than millions of years. But objects larger than about 100 feet like DA14 are believed to strike Earth every few hundred years. At this time there are no known asteroids of this size on a collision course with Earth for at least 100 years.
What’s of interest and concern, however, is that scientists believe there are literally tens to hundreds of thousands of objects, mostly with dimensions in the hundreds of feet, whizzing around in space that have not yet been discovered. Consider the fact that XE54 was first observed only the day before its closest approach. Even though it has been crossing Earth’s orbit about once per year for millennia, DA14 was discovered less than one year ago.
NASA video overview of asteroid 2012 DA 14
(Note: the discovery of DA14 reads like the opening of a SciFi movie. Last February, a young dental surgeon sailing along the Mediterranean coast of Spain just happened to spot a speck of light moving across the sky in images on his laptop from an observatory several hundred miles away. He alerted the Minor Planet Center in Cambridge, Massachusetts. Telescopes around the world then began determining the previously unknown object’s orbit placed it on a near–collision with the Earth.)
For the foreseeable future, then, Earth will continue to reside in a cosmic shooting gallery with an enormous number of currently unknown objects, some of which may have a direct bead on us without our knowing. While it is probably much more unlikely than likely, a potentially disastrous collision with an asteroid of at least the dimensions comparable to DA14 could occur anytime possibly with little or no warning in our lifetimes.
Over the next decade or so, ongoing and proposed (but not yet approved and/or funded) improvements in earth and space-based asteroid monitoring capabilities should (could) reduce the number of possible close encounters of the asteroid kind. For example, most of the sky seen from the southern hemisphere is currently unobserved by asteroid watchers. However this void is expected to be at least partially filled in 2019 by the Large Synoptic Survey Telescope (LSST) on Cerro Pachón Mountain in Chile.
Because ground-based telescopes can operate only at night, objects coming from the direction of the sun cannot be monitored. Only space-based platforms can overcome this problem. Despite a recent United Nations meeting of experts designed to review issues and discuss plans for the future, the only hard and potentially realistic proposal on the books comes from a non-profit charitable organization organized by notable scientists and two former NASA astronauts. All well and good, except the project depends upon contributions to move forward.
(Note: the company is also planning to mine asteroids for minerals and water for future manned exploration of space. While it’s not feasible to return very much of an asteroids resources back to Earth, it’s estimated that, if it were possible, the value of the asteroid belt between the orbits of Mars and Jupiter amounts to the equivalent of about 100 billion dollars for every person on Earth today!)
Suppose we were able to spot an asteroid on a trajectory that threatens Earth. What, if anything, could be done to avoid a potential disaster? The answer depends mostly on how much advance warning is available, especially for a potential “extinction event” sized object. Without advanced planning and defenses of some sort in place (not likely, politically and economically speaking), estimates are that it would take 10-20 years to spin up and effectively implement an operational system and strategy. As discussed previously, this would most likely take the form of deflecting the asteroid from its trajectory by gradually bumping (“nudging”) it with a robot space vehicle. Complicating any deflection strategy is that 15 percent of asteroids with orbits that bring them within close proximity of Earth are binary, i.e., a pair of objects orbiting about one another.
(Science fiction author Larry Niven is quoted as saying:“The dinosaurs became extinct because they didn’t have a space program. And if we become extinct because we don’t have a space program, it’ll serve us right!” If dinosaurs had been able to divert the killer asteroid, we wouldn’t be around to contemplate the event.)
If we were threatened by the more common mid-sized asteroid like DA14, the same deflection approach could be applied, but this class of asteroid would unlikely provide adequate warning time for this bumping strategy to sufficiently alter the trajectory.
Then what? Probably just sit back and watch coverage of the awe-inspiring (not panic-generating) event on 24/7 cable TV assuming there was total confidence (never possible with weather forecasts) the asteroid would crash into the ocean (but be wary of a tsunami from the impact.)
If ground zero were a populated region for an incoming medium-sized asteroid, blowing it up with a nuclear missile is a possibility. However, this probably would result in large fragments raining down on the surface. The net result might be a more extreme hazard over a larger area than a direct hit. Either way, the scenario becomes one of evacuating the affected population and massive disaster mitigation efforts.
Whether or not an asteroid threatens Earth in my lifetime - notwithstanding the extensive media coverage of this event has received - I personally am not going to lose much sleep over it.
What does keep me up at night – or at least thinking a lot about, is the more likely and possibly more imminent hazard presented by an end to life as we know it from a solar storm. I’ll have status report on this very real concern in a forthcoming post. (Spoiler alert: complacency given by the relative quiescence of the sun as the solar max approaches is far from warranted.)
NASA Asteroid flyby will be closest for a space rock so large (Washington Post, Brian Vastag)