is an Aten asteroid

Aten asteroid

The Aten asteroids are a group of near-Earth asteroids, named after the first of the group to be discovered . They are defined by having semi-major axes of less than one astronomical unit...

 located in Venus

Venus

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

' zone of influence that has frequent close encounters with Mercury

Mercury (planet)

Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

, Venus, and Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. It is also one of the best studied potentially hazardous asteroids.

Low aphelion

was discovered on November 25, 1998, by LINEAR

Linear

In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...

 about four months after a particularly close encounter with the planet Mercury (about 0.047 au

Astronomical unit

An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

). At the time of its discovery, astronomers were trying to find the first Apohele asteroid

Apohele asteroid

Apohele asteroids, or alternatively Interior-Earth Objects or Atira asteroids, are a subclass of Aten asteroids. They have not only their perihelion within Earth's orbit, but also their aphelion; that is, their entire orbit is within Earth's .The first suspected Apophele was , the first confirmed...

 (one that is always closer to the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 than the Earth). All asteroids known at the time that got closer to the Sun than the Earth also crossed Earth's orbit. Earlier that year, David J. Tholen

David J. Tholen

David James Tholen is an American astronomer at the Institute for Astronomy of the University of Hawaii, who specializes in planetary and solar system astronomy.-Professional life:...

 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 (1.019 au), 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 (aphelion = 1.013 au). 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

Venus

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

 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

(99907) 1989 VA

1989 VA is an Aten asteroid located in Venus' zone of influence that has frequent close encounters with the Earth. It was discovered on 2 November 1989 by C. S., E. M. Shoemaker and David H...

, 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

Trojan asteroid

The Jupiter Trojans, commonly called Trojans or Trojan asteroids, are a large group of objects that share the orbit of the planet Jupiter around the Sun. Relative to Jupiter, each Trojan librates around one of the planet's two Lagrangian points of stability, and , that respectively lie 60° ahead...

 and horseshoe

Horseshoe orbit

A horseshoe orbit is a type of co-orbital motion of a small orbiting body relative to a larger orbiting body . The orbital period of the smaller body is very nearly the same as for the larger body, and its path appears to have a horseshoe shape in a rotating reference frame as viewed from the...

 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 one is currently a co-orbital.

Record close encounter

is a Potentially Hazardous Asteroid (PHA). 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 December 16, 2001, it became the first Potentially Hazardous Asteroid to be observed passing within 5 Lunar Distances

Lunar distance (astronomy)

In astronomy, a lunar distance is a measurement of the distance from the Earth to the Moon. The average distance from Earth to the Moon is 384,400 kilometers...

 (the average distance between the Earth and the Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

) from the Earth. Other asteroids have come closer, and several 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 Potentially Hazardous Asteroid has made since passed by in 1969. However, was not discovered until many years after its closest approach, so no one knew it came at the time.

In September of 2004, the well known Potentially Hazardous Asteroid 4179 Toutatis

4179 Toutatis

4179 Toutatis/1989 AC is an Apollo, Alinda, and Mars-crosser asteroid with a chaotic orbit produced by a 3:1 resonance with the planet Jupiter, a 1:4 resonance with the planet Earth, and frequent close approaches to the terrestrial planets...

 came about 4 Lunar Distances from Earth. Due to its diameter being over ten times larger (5.7 km) and its closer approach, Toutatis at its closest (mag 8.9) was about half a magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 brighter than was at its closest (mag 9.5). 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.

Frequent inner-planet encounters

is a Mercury-crosser asteroid, a Venus-crosser asteroid

Venus-crosser asteroid

A Venus-crosser is an asteroid whose orbit crosses that of Venus. The known numbered Venus-crossers and outer-grazers are listed below .Venus also has a quasi-satellite, 2002 VE68...

, and an Earth-crosser asteroid

Earth-crosser asteroid

An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. The known numbered Earth-crossers are listed here. Those Earth-crossers whose semi-major axes are smaller than Earth's are Aten asteroids; the remaining ones are Apollo...

. Because of its relatively low inclination (7.34°), it is able to come close to each of these planets. Its orbit takes it within 0.021 au of Mercury's orbit, 0.0368 au of Venus' orbit, and 0.00989 au of Earth's orbit. It makes frequent encounters with these inner planets. The last time it came close to Mercury, Venus and Earth was 1998, 1977, and November 12, 2004 respectively. The next such encounter will be in 2035. These encounters perturb its orbit parameters slightly, and each pass reduces its inclination further. Astronomers have to monitor it closely due to its frequently changing path.

Physical Characteristics

During its close encounter in 2001, astronomers were able to make radar images of its surface and determine physical properties that remain unknown for most asteroids. The asteroid measures 420 by 330 metres (modestly elongated) and completes one rotation every 3.70 hours. It is classified a type E/Xe asteroid.

Future flyby candidate

has an orbit that not only crosses Earth's orbit, but is roughly parallel to it at its furthest. This means that during favourable years it is easy to reach from Earth. Several times this decade, it will be an easier target than Earth's own Moon. It is high on the list of possible Near-Earth Asteroid targets for future flybys, landings, mining, or orbit manipulations.

External links

• IMAGES OF ASTEROID 1998 WT24 - NASA
  NASA
  The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
  
  
• Radar Investigations of Asteroid 33342 (1998 WT24) in December 2001 with Evpatoria-Medichina and Goldstone-Medichina Bistatic Systems