A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun (perihelion) is less than 1.3 times the Earth–Sun distance. This definition applies to the object's orbit around the Sun, rather than its current position, thus an object with such an orbit is considered an NEO even at times when it is far from making a close approach of Earth. If an NEO's orbit crosses the Earth's orbit, and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but about 0.35% are comets.
A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and which is large enough to cause significant regional damage in the event of impact. They are conventionally defined as having a minimum orbit intersection distance with Earth of less than 0.05 astronomical units and an absolute magnitude of 22 or brighter, the latter of which roughly corresponds to a size larger than 140 meters. More than 99% of the known potentially hazardous objects are no impact threat over the next 100 years. As of September 2022, just 17 of the known potentially hazardous objects listed on the Sentry Risk Table could not be excluded as potential threats over the next hundred years. Over hundreds if not thousands of years though, the orbits of some "potentially hazardous" asteroids can evolve to live up to their namesake.
2012 TC4 is a tumbling micro-asteroid classified as a bright near-Earth object of the Apollo group, approximately 10 meters (30 feet) in diameter. It was first observed by Pan-STARRS at Haleakala Observatory on the Hawaiian island of Maui, in the United States. As of 1 October 2017, it had a small Earth minimum orbital intersection distance of 0.000149 AU (22,300 km). On 12 October 2017, it passed Earth at 0.00033524 AU (50,151 km). The asteroid was removed from the Sentry Risk Table on 16 October 2017 and with a 5-year observation arc has a well-known orbit. For example, on the previously risk-listed date of 12 October 2022, it is now known that the asteroid will be more than 3 AU (450 million km) from Earth.
2013 TX68 is an Apollo asteroid and near-Earth object discovered on 6 October 2013 by the Catalina Sky Survey, during which it was near a close approach of 5.4 Lunar distances (LD) from the Earth. The asteroid only has a 10-day observation arc which makes long-term predictions of its position less certain. It was observed for three days as it approached Earth in the night sky starting with the sixth of October, 2013. Then it became unobservable by being between the Earth and the Sun, then not recovered due to its small size and dimness. Precovery images by Pan-STARRS from 29 September 2013 were announced on 11 February 2016 that extended the observation arc to 10 days. It was removed from the Sentry Risk Table on 11 February 2016, so there is no risk of impact from this object for the next hundred years or more. The asteroid was last observed on 9 October 2013.
469219 Kamoʻoalewa, provisionally designated 2016 HO3, is a very small asteroid, fast rotator and near-Earth object of the Apollo group, approximately 40–100 meters (130–330 feet) in diameter. At present it is a quasi-satellite of Earth, and currently the second-smallest, closest, and most stable known such quasi-satellite (after 2023 FW13). The asteroid was discovered by Pan-STARRS at Haleakala Observatory on 27 April 2016. It was named Kamoʻoalewa, a Hawaiian word that refers to an oscillating celestial object. The object's Earth-like orbit and its composition of lunar-like silicates may be a result of it being lunar ejecta.
2010 WC9, unofficially designated ZJ99C60, is a sub-kilometer near-Earth asteroid of the Apollo group, approximately 100 meters (330 feet) in diameter. First observed for eleven days by the Catalina Sky Survey in 2010, the asteroid was recovered in May 2018 during its sub-lunar close encounter with Earth.
2011 ES4 (also written 2011 ES4) is an Apollo near-Earth asteroid roughly 22–49 meters (72–160 feet) in diameter. It was first observed on 2 March 2011 when the asteroid was about 0.054 AU (8,100,000 km; 5,000,000 mi) from Earth and had a solar elongation of 159 degrees. It passed closest approach to Earth on 13 March 2011. Before the 2020 approach, the asteroid had a short observation arc of 4 days and had not been observed since March 2011. The asteroid was expected to pass within 1 lunar distance of Earth in early September 2020, but did not. There was no risk of a 2020 impact because the line of variation (LOV) did not pass through where Earth would be, and the closest possible 2020 Earth approach was about 0.00047 AU (70,000 km; 44,000 mi). One line of variation showed the asteroid passing closest to Earth on 5 September 2020 at 0.06 AU (9,000,000 km; 5,600,000 mi) with a magnitude of 23, which would place it near the limiting magnitude of even the best automated astronomical surveys.
2020 QG, also known by its internal designation ZTF0DxQ, is an Earth-crossing asteroid, a few meters in diameter. It belongs to the Apollo group, and passed above the surface of Earth approximately 2,950 kilometres (1,830 mi) away on 16 August 2020 at 04:09 UT. It was first imaged by the Zwicky Transient Facility (ZTF) at the Palomar Observatory about 6 hours after this closest approach, and was later identified by Kunal Deshmukh, a student at the Indian Institute of Technology Bombay, along with colleagues Kritti Sharma, Chen-Yen Hsu and Bryce T. Bolin analyzing images from the ZTF.
2019 BE5 is a sub-kilometer near-Earth asteroid classified under the Aten group. It was discovered on 31 January 2019, by the Zwicky Transient Facility at the Palomar Observatory. The asteroid was discovered one day after it had made a close approach to Earth from a distance of 0.00784 AU (1.173 million km; 3.05 LD).
(231937) 2001 FO32 is a near-Earth asteroid classified as a potentially hazardous asteroid of the Apollo group. With an estimated diameter around 550 m (1,800 ft), it was discovered by the Lincoln Near-Earth Asteroid Research at Socorro, New Mexico on 23 March 2001. The asteroid safely passed by Earth on 21 March 2021 16:03 UTC from a closest approach distance of 0.0135 AU (2.02 million km; 1.25 million mi), or 5.25 lunar distances (LD). During the day before closest approach, 2001 FO32 reached a peak apparent magnitude of 11.7 and was visible to ground-based observers with telescope apertures of at least 20 cm (8 in). It is the largest and one of the fastest asteroids to approach Earth within 10 LD (3.8 million km; 2.4 million mi) in 2021.
![Plot of orbits of known Potentially Hazardous Asteroids (size over 140 m [460 ft] and passing within 7.6 million km [4.7 million mi] of Earth's orbit) as of early 2013 (alternate image) Potentially Hazardous Asteroids 2013.png](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f6/Potentially_Hazardous_Asteroids_2013.png/550px-Potentially_Hazardous_Asteroids_2013.png)
