An artist's illustration of a large asteroid headed for Earth.
This diagram illustrates the differences between orbits of a typical near-Earth asteroid (blue) and a potentially hazardous asteroid, or PHA (orange). PHAs have the closest orbits to Earth's orbit, coming within 5 million miles (about 8 million kilometers), and they are large enough to survive passage through Earth's atmosphere and cause significant damage.
This chart illustrates how infrared is used to more accurately determine an asteroid's size.
This radar image of asteroid 2005 YU55 was obtained on Nov. 7, 2011, at 11:45 a.m. PST (2:45 p.m. EST/1945 UTC), when the space rock was at 3.6 lunar distances, which is about 860,000 miles, or 1.38 million kilometers, from Earth.
This still from a NASA animation by Jon Giorgini of the Jet Propulsion Laboratory shows the trajectory of asteroid 2005 YU55 as it passes between Earth and the moon on Nov. 8, 2011.
This radar image of potentially hazardous asteroid 1999 RQ36 — the target of NASA's Osiris-Rex sample-return mission — was obtained by NASA's Deep Space Network antenna in Goldstone, Calif. on Sept 23, 1999.
An artist's illustration of asteroid Apophis near Earth. The asteroid will fly extremely close to Earth in 2029, and then again in 2036, but poses no threat of hitting the planet either time.
ESA’s Herschel Space Observatory captured asteroid Apophis in its field of view during the approach to Earth on January, 5-6, 2013. This image shows the asteroid in Herschel’s three PACS wavelengths: 70, 100 and 160 microns.
The orbit of asteroid 2011 AG5 carries it beyond the orbit of Mars and as close to the sun as halfway between Earth and Venus.
Minor planet 6344 P-L (=2007 RR9) among the stars on October 3, 2007. This is currently still a faint object, recorded in 3-minute exposures tracked on the target object by Paulo Holvorcem of Brazil, remotely using the 0.35-m telescope at Tenagra Observatory in Western Australia (at Shenton Park, near Perth) operated by Paul Luckas.
NEOWISE survey has found that more potentially hazardous asteroids, or PHAs, are closely aligned with the plane of our solar system than previous models suggested. PHAs are the subset of near-Earth asteroids (NEAs) with the closest orbits to Earth's orbit, coming within 5 million miles (about 8 million kilometers).
NASA's NEOWISE asteroid survey indicates that there are at least 40 percent fewer near-Earth asteroids in total that are larger than 330 feet, or 100 meters. NASA used its WISE infrared space telescope to make the find.
The asteroid 2012 KP24 flew past Earth on May 28, 2012. While the space rock passed within the moon's orbit, it did not pose any danger to the planet.
An artist's illustration of an asteroid flying near Earth.
This NASA diagram shows the orbit of newfound asteroid 2011 SM173, which flew within 180,000 miles of Earth on Sept. 30, 2011. The asteroid was discovered a day earlier on Sept. 29.
An object entered the atmosphere over the Urals early in the morning of Feb. 15, 2013. The fireball exploded above Chelyabinsk city, and the resulting overpressure caused damage to buildings and injuries to hundreds of people. This photo was taken by Alex Alishevskikh from about a minute after noticing the blast.
This video still image shows damage created by the meteor that exploded over the Chelyabinsk region of Russia on Feb. 15, 2013.
The Tunguska explosion flattened some 500,000 acres of Siberian forest on June 30, 1908. This image is from the Leonid Kulik expedition in 1927.
A 130-foot-meteor created the mile-wide Meteor Crater in Arizona. The comet proposed to have impacted life in North America was significantly larger, but no crater indicating its collision has been found.
Astronaut Clayton C. Anderson tweeted this picture from space, a view of Aorounga Impact Crater, southeast of of Emi Koussi volcano in Chad.
Landsat image (color composite) of the newfound Kebira Crater in the Western Desert of Egypt at the border with Libya. The outer rim of the crater is about 19 miles (31 km) in diameter. Image courtesy of Boston University Center for Remote Sensing
Artist’s impression of a 6-mile-wide asteroid striking the Earth. Scientists think approximately 70 of these dinosaur killer-sized or larger asteroids hit Earth between 3.8 and 1.8 billion years ago.
An artist rendering of a space rock streaking toward Earth. Most experts think an impact off the Yucatan Peninsula 65 million years ago was the primary cause of the dinosaur demise. Others think volcanism and climate change may have played a role. A new and controversial idea suggests there was another, larger impact in India that was responsible.