Move over, Bruce Willis. Your asteroid-pulverizing, Home Planet–saving career might not be ready for a resurgence just yet, although NASA will still be carefully tracking the visit of 2012 DA14, a small rocky body which will make its closest approach to Earth at around 2:25 p.m. EST today. Known as a “Near-Earth Object” (NEO), it is expected to pass within 17,150 miles of us, and the Jet Propulsion Laboratory in Pasadena, Calif., will air a half-hour broadcast with real-time animations of the celestial intruder and views from observatories in Australia and Europe. It will be a unique opportunity for researchers to study the mysteries of an NEO, up close and personal.
As described by Jason Rhian in a recent AmericaSpace article, the asteroid measures about 150 feet wide and has an estimated mass of 190,000 metric tons. Our planet’s immense gravity will distort its path in such a fashion that in all likelihood it will not come our way again. Yet 2012 DA14 will still pass far closer than our Moon—which orbits the Earth at a mean distance of 240,000 miles—and at a peak magnitude of 7.2 it might be visible to ground-based skywatchers with telescopes or high-powered binoculars. Any possibility that it will strike a satellite is considered remote, and current trajectory models indicate that it will pass no closer than 1,200 miles from any of our mechanical moons. Still, controllers have been provided with orbital parameters and other pertinent data for the asteroid.
NASA’s commentary and near-real-time imagery of the flyby will be streamed from noon EST throughout this afternoon at http://www.ustream.tv/nasajpl2, and the agency’s Marshall Space Flight Center of Huntsville, Ala., will stream its own feed from 9:00 p.m. EST at http://www.ustream.tv/channel/nasa-msfc.
“We’ve done a pretty good job of finding asteroids that are one kilometer or larger that could potentially impact the Earth,” said Lindley Johnson, program executive with NASA’s NEO Observations Program at the agency’s headquarters in Washington, D.C. “Our estimates show that we’ve found about 95 percent of those larger asteroids that come close to the Earth. We’ve also found smaller objects, like DA14.” That “find” occurred on 23 February 2012, by astronomers at the Observatorio Astronómico de La Sagra in Granada, Spain, when the NEO was about 1.6 million miles away. Today’s event is considered to be a record close approach for a known object of 2012 DA14’s size and mass.
And for those of us planning to watch out for the asteroid, the best viewing location is believed to be Indonesia, although Eastern Europe, Asia, and Australia should be well-placed to see it. Goldstone Observatory in the Mojave Desert, near Barstow, Calif., will observe 2012 DA14 by radar for the next few days. Following that, it will pass us again in February 2046, but at a much greater distance of around 930,000 miles, and the chance of it actually hitting us at any point between 2080 and 2111 is considered infinitesimally small: the risk has been described as 0.00000021% … or a 1 in 4.7 million probability. On the 0-10 Torino Scale, which categorizes the risks posed by NEOs, today’s visitor is listed as “0” or “White,” meaning that it poses no hazard to us.
Yet it is events such as these which reinvigorate our awareness of the risks that NEOs pose. Nowhere are these risks more prevalent—or famous—than at the site of the Chicxulub Crater in Mexico’s Yucatan Peninsula, whose ancient impact is generally accepted to have been responsible for the extinction of most non-avian dinosaurs, around 65 million years ago. On the Torino integer list, that impact would have been a top-of-the-scale “10” (or “Red”) event, described as being “capable of causing global climatic catastrophe that may threaten the future of civilization as we know it … whether impacting land or ocean. …” Less catastrophic (9-8) Red events might also trigger localized tsunamis or major devastation. Thankfully, events such as these occur on average once every 100,000 years or so.
Lower down on the Torino Scale, ranking between 7-5, “Orange” events would require governmental (or intergovernmental) contingency planning if they were predicted to occur within the next few decades, whilst lower still the “Yellow” (4-2) events merit close attention from astronomers and possibly public officials and “Green” and “White” (from 1-0) pose almost no risk. And that is fortuitous, indeed, for if 2012 DA14 were to have hit us, it would have entered the Earth’s atmosphere at around 28,400 mph, producing an air burst equivalent of 2.9 megatons of TNT at an altitude of 28,000 feet.
To put that in context, the Tunguska explosion in Siberia in June 1908—the largest impact event ever recorded in human history—generated an air burst of 3-20 megatons, flattened 80 million trees over 830 square miles, incinerated thousands of reindeer, bears, wolves, foxes, and other animals … and, had it hit a metropolitan area, would undoubtedly have caused enormous carnage in what is ominously described as “a city-killer.” If Tunguska was caused by an NEO, it probably measured around 330 feet wide, a little more than double the size of 2012 DA14, offering a measure of perspective of what we have just dodged.
As today’s asteroidal visitor makes its relatively close, but relatively harmless, passage to the Home Planet today, wherever you are, it is fortunate that you will be left alone to live in peace, work in peace, skywatch in peace, eat in peace, or sleep in peace.
At least, for now.