Asteroid attacks: Close calls getting closer all the time (pictures)

On Friday an asteroid 150 feet in diameter will pass by Earth. It will be a relatively close call -- the pass will be a record-close approach for a known object of this size.
Though it won't be visible with the naked eye, as it's fairly small, asteroid 2012 DA14 should be visible to viewers in Eastern Europe, Asia, and Austraila using a telescope or a pair of binoculars. It will pass inside the ring of Earth's geosynchronous weather and communications satellites, coming within just 17,200 miles of the Earth's surface at around 12:30 p.m. PT.
Twenty years ago, NASA would not even have been able to detect this threat to Earth, but 15 years ago NASA established the Near Earth Object Program, known by many by its nickname "Spaceguard." With the original goal of finding 1km or larger objects which might be threats, the program has been quite a success, having found 95 percent of those 1km or larger size asteroids, NASA says, but they have also notably found many smaller asteroids, such as the approaching 2012 DA14.
You can following the Near Earth Object Program on Twitter at @asteroidwatch for up to date information on potentially hazardous asteroids and comets that could approach Earth.

Discovery of these potentially hazardous asteroids and comets involves dedicated telescopes sweeping the sky. Detection occurs simply by observing the motion of asteroids against the background stars.
By bouncing radar waves off an asteroid, researchers have been able to get detailed physical measurements along with very specific information about near Earth asteroids, which might one day help as NASA searches for targets for manned missions or mining operations.
Discovered in 2005, 2005 YU55, seen here, passed within 201,900 miles of Earth on November 8, 2011. Observed by the Goldstone Deep Space Communications Complex (GDSCC) in the Mojave Desert, the object was measured by radio waves and found to be about 400m in diameter, about the size of an aircraft carrier. NASA says we won't be getting detailed images like these from 2012 DA14 because the asteroid is much smaller.
See a five-frame looped movie of the 2005 YU55 radar imagery here.

Last year, NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) survey found that more potentially hazardous asteroids, or PHAs, are closely aligned with the plane of our solar system than previous models had suggested.
PHAs are the subset of near-Earth asteroids (NEAs) with the closest orbits to Earth's orbit, coming within 5 million miles. They are also defined as being large enough to survive passage through Earth's atmosphere and cause damage on a regional, or greater, scale.
The dots represent a snapshot of the population of NEAs and PHAs that scientists think are likely to exist based on the NEOWISE survey. Positions of a simulated population of PHAs on a typical day are shown in bright orange, and the simulated NEAs are blue. Earth's orbit is green.
These results have found about 4,700 objects, plus or minus 1,500, with diameters larger than 330 feet. The NEOWISE team estimates that only about 20 percent to 30 percent of the PHAs thought to exist have actually been discovered so far.

The Torino Scale, created by Professor Richard P. Binzel in the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology, is a color coded and numbered scale ranking the threats to Earth from asteroids and comets.
When a new asteroid or comet is discovered, initial predictions for where the object will be months or decades in the future are rough estimates, and subject to changes based on collecting additional data.
Fortunately, for the majority of objects even the initial calculations are sufficient to show that they will not make any close passes by the Earth within the next century.

In this oblique view, a diagram shows the path of near-Earth asteroid 2012 DA14 as it is seen passing close to Earth on February 15, 2013.
The asteroid will quickly move from the southern evening sky into the northern morning sky with its closest Earth approach occurring at about 12:26 p.m. PT when it will achieve a magnitude of less than seven, which is somewhat fainter than naked eye visibility. Viewers in Eastern Europe, Asia, and Australia should be able to view the asteroid with the help of binoculars.

Radar image of asteroid Toutatis taken by NASA's Goldstone Solar System Radar on December 12 and 13, 2012.
On December 12, 2012, the day of its closest approach to Earth, the 3-mile long Toutatis was 4.4 million miles away. In these radar images, the elongated, irregularly shaped object shows ridges and craters and a very slow, tumbling rotational state, rotating on its long axis every 5.4 days.
See a short, 64 frame video of the asteroid Toutatis generated from data taken by Goldstone's Solar System Radar.

Nine new radar images of near-Earth asteroid 2007 PA8 were obtained between October 31 and November 13, 2012, with data collected by NASA's 230-foot-wide Deep Space Network antenna at Goldstone, Calif.
These new radar images and measurements of 2007 PA8's distance and line-of-sight velocity further refined calculations of its orbit around the sun, enabling reliable computation of the asteroid's motion for the next 632 years.

An impact with Earth has been ruled out in 2029 for Asteroid Apophis, which was discovered on June 19, 2004.
Alarm bells went off when the initial data suggested there was a fairly large, 2.7 percent chance of the asteroid impacting Earth in 2029. Apophis broke the record for the highest level on the Torino Scale when it was categorized as a level 4 threat -- for a short time -- before it was lowered to 1 and then determined to be of no threat in August 2006.
Nonetheless, the April 13, 2029 fly-by will be quite an event. The asteroid, which is the size of three football fields, will come within 19,400 miles of the Earth's surface, according to the Near-Earth Object Program Office at JPL.
According to NASA and the Near Earth Object Program, we can expect an Earth impact from an asteroid the size of Apophis, around 325 meters, about every 80,000 years or so.
Want to learn more about the devastating effect of an Earth impact? Calculate your chances for survival here.