"NASA states that the odds are 300 to 1 that asteroid 1950DA will hit the Earth, but says there's plenty of time to figure out what to do before it does." http://en.wikipedia.org/wiki/(29075)_1950_DA 1950 DA is the near Earth object with the highest known possible probability of impacting Earth, according to the Palermo Technical Impact Hazard Scale. For a few days in December 2004 [its threat-risk] was temporarily surpassed by 99942 Apophis (which at the time was named only by its provisional designation 2004 MN4). 1950 DA was first discovered on February 23, 1950 by Carl A. Wirtanen at Lick Observatory. It was observed for 17 days and then lost for half a century. An object discovered on December 31, 2000 (provisionally designated 2000 YK66) was recognized as being the 1950 DA. If 1950 DA continues on its present orbit, it will approach near to the Earth on March 16, 2880. Over the intervening time, the rotation of the asteroid will cause its orbit to change (by the Yarkovsky effect). The radar observations are currently being reanalyzed, in combination with the optical lightcurves. http://www.geocities.com/blobrana/features/1950da.html Integration of the orbit of asteroid (29075) 1950 DA, based on radar and optical measurements spanning 51 years, reveals a 20-minute interval in March 2880 when there could be a non-negligible probability of the 1-kilometer object colliding with Earth. The impact scenario is three orders of magnitude more probable than any previous case, or about 1.5 times greater than the entire background risk through the year 2880, but depends on the physical properties of the asteroid. Trajectory knowledge remains accurate until 2880 because of extensive astrometric data, an inclined orbit geometry that reduces in-plane perturbations, and an orbit uncertainty space modulated by gravitational resonance. Analysis of sources of uncertainty in this long-term prediction include the effects of numerical integration error, galactic tides, perturbations due to encounters with other asteroids, solar mass loss, solar particle-wind, solar oblateness and radiation pressure, the uncertainties in planetary masses, and accelerations due to the time-delayed anisotropic thermal re-radiation of incident solar radiation, also known as the ``Yarkovsky" effect. This latter effect depends on the shape, mass, spin axis, composition, and surface properties of the asteroid, all of which are either unknown or weakly determined, such that refinement to a specific collision probability may require direct inspection by a spacecraft If you add the Yarkovskey effect, it could be this asteroid doesn't have a chance of hitting us," - Joseph Spitale, Lunar and Planetary Laboratory at the University of Tucson, Ariz.
So far scientists still aren't sure how or even if the Yarkovsky effect will change the trajectory of 1950 DA.
A preliminary analysis shows two possible pole directions (Giorgini, et al., 2002 "Asteroid 1950 DA's 2880 Encounter with Earth"). One trajectory misses the Earth by tens of millions of kilometers, while the other has an impact probability of 1⁄300. The energy released by a collision with an object the size of 1950 DA would cause major effects on the climate and biosphere which would be devastating to human civilization. Results of a study simulating the impact of a 1950 DA-like object in the northern Atlantic ocean were published (Ward & Asphaug, UCSD, June issue of the Geophysical Journal International). The same impact velocity and general impact region were used, but a less massive object with less energy dissipation was assumed. The actual mass of 1950 DA is unknown. It was found waves propagate throughout the Atlantic Ocean and the Caribbean. Two hours after impact, 400-foot waves reach beaches from Cape Cod to Cape Hatteras. Four hours after impact, the entire East Coast experiences waves at least 200 feet high. It takes 8 hours for the waves to reach Europe, where they come ashore at heights of about 30 to 50 feet.
The discovery of the potential impact has heightened interest in asteroid deflection strategies. ----------- http://www.sciam.com/article.cfm?articleID=0005979A-3A5E-1D23-97CA809EC588EEDF | July 08, 2002 | | Avoiding the Impact | | After last month's near miss with an asteroid 100 meters in diameter, a former astronaut discusses what to do about the danger to Earth from huge space rocks | From Shooting Stars to Smashing Siberia Asteroids circle the sun on paths that may cross the orbit of Earth. From time to time through history, huge asteroids have collided with the planet. "The reality is we get hit 100,000 times every day; but they’re so small, you call them shooting stars," Schweickart says. Earth's atmosphere protects us from bodies smaller than 50 meters. "But when they get to the size of 50 meters, they start coming though the atmosphere instead of burning up in it. The Tunguska thing didn’t make it to the ground, but it blew up so close to the ground that it flattened a big hunk of Siberia." The famous 1908 explosion at Tunguska leveled 2,000 square kilometers of forest. It involved an asteroid some 100 meters in diameter. Impacts with bodies that size may occur once in a century on average, according to estimates. Though far less frequent, an asteroid of 10 to 15 kilometers in size could wreak the kind of destruction that wiped out the dinosaurs 65 million years ago, says Schweickart. Impacts of that size occur perhaps once in every 1,000,000 centuries, according to the JPL Near Earth Asteroid Tracking Team.
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