(33342) 1998 WT24
is a bright, sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Aten group, located in Venus's zone of influence that has frequent close encounters with Mercury, Venus, and Earth. It made a close approach to Earth on 11 December 2015, passing at a distance of about 4.2 million kilometers and reaching about apparent magnitude 11.
The asteroid was discovered on 25 November 1998 by LINEAR about four months after a close encounter with the planet Mercury. It measures approximately 400 meters in diameter. It is also one of the best studied PHAs and was the 10th Aten asteroid to be numbered.
Classification and orbit
orbits the Sun at a distance of 0.42–1.02 AU once every 7 months. Its orbit has an eccentricity of 0.42 and an inclination of 7° with respect to the ecliptic.Low aphelion
At the time of its discovery, astronomers were trying to find the first Apohele asteroid. All asteroids known at the time that got closer to the Sun than Earth also crossed Earth's orbit. Earlier that year, David J. Tholen claimed to have spotted the first Apohele asteroid, which was dubbed. However, the object was lost without being confirmed. Thus, 1993 DA remained the asteroid with the lowest known aphelion at 1.023 AU. When was discovered, it was found to have a slightly smaller aphelion than 1993 DA, and was thus the closest thing to an Apohele asteroid known at the time. It lost its smallest aphelion title almost immediately when was discovered only a few weeks later. Asteroids with even smaller aphelions were discovered until February 2003, when finally, an asteroid with an aphelion smaller than 1.000 AU was discovered. This was 163693 Atira, the first confirmed Apohele asteroid.Venus zone of influence
was the second asteroid discovered to be close enough to Venus as to be within the major planet's zone of influence. It is located at about the inner edge of the zone, while (99907) 1989 VA, the first asteroid discovered there, is at about the outer edge. It is possible for planets to capture asteroids located in their sphere of influences into co-orbital relationships such as Trojan and horseshoe asteroids. Because of its frequent close encounters with Mercury and Earth, however, it may prove difficult for Venus to keep in a co-orbital relationship for any length of time. Of the six objects in Venus's zone of influence, only Zoozve is currently a co-orbital.Record close encounter
is a potentially hazardous asteroid. That means its orbit takes it very close to Earth and if it were to collide with our planet, it would cause devastation on at least a regional scale. On 16 December 2001, it became the first PHA to be observed passing within 5 Lunar Distances from Earth. Other asteroids have come closer, and numerous have even come closer than the Moon, but these have all been small asteroids, incapable of causing much damage to the planet, or much concern. The 2001 encounter was the closest known approach to Earth any PHA had made since passed by on 27 August 1969. However, was not discovered until September 1999 many years after its closest approach, so no one knew about in 1969.| Date | Distance from Earth |
| 1908-12-16 | |
| 1956-12-16 | |
| 2001-12-16 | |
| 2099-12-18 |
In September 2004, the well known PHA 4179 Toutatis came about 4 Lunar Distances from Earth. Due to its diameter being over ten times larger and its closer approach, Toutatis at its closest was about half an apparent magnitude brighter than was at its closest. However, Toutatis arrived during a full moon, and thus 's 2001 encounter is still the most easily observed flyby of an asteroid in history. It also made the first Near-Earth asteroid observed to be brighter than magnitude 10.