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2005 HC₄

Discovery
Discovered by	LONEOS
Discovery date	30 April 2005
Designations
Minor planet category	Mercury Crosser Venus Crosser Apollo Asteroid Mars Crosser
Orbital characteristics
Epoch 3 May 2005 (JD 2453493.5)
Uncertainty parameter 9
Aphelion	3.5707 AU (534.17 Gm)
Perihelion	0.070657 AU (10.5701 Gm)
Semi-major axis	1.8207 AU (272.37 Gm)
Eccentricity	0.96119
Orbital period (sidereal)	2.46 yr (897.30 d)
Mean anomaly	341.42°
Mean motion	0° 24 4.32 /day
Inclination	8.3967°
Longitude of ascending node	63.790°
Argument of perihelion	309.01°
Earth MOID	0.0615074 AU (9.20138 Gm)
Jupiter MOID	1.92798 AU (288.422 Gm)
Physical characteristics
Dimensions	210–480 m
Absolute magnitude (H)	20.7

2005 HC₄ is the asteroid with the smallest known perihelion of any known object orbiting the Sun (except sungrazing comets). Its extreme orbital eccentricity brings it to within 0.071 AU of the Sun (23% of Mercury's perihelion) and takes it as far as 3.562 AU from the Sun (well beyond the orbit of Mars). Due to its very small perihelion and comparably large aphelion, 2005 HC₄ achieves the fastest speed of any known asteroid bound to the Solar System with a velocity of 157 km/s (565,000 km/h; 351,000 mi/h) at perihelion (there are comets, however, which obtain much higher speeds).

See also

• List of Mercury-crossing minor planets
• List of Venus-crossing minor planets
• Apollo asteroids
• List of Mars-crossing minor planets

References

1. "MPEC 2005-J02 : 2005 HC4". IAU Minor Planet Center. 1 May 2005. Retrieved 5 March 2014. (K05H04C)
2. "JPL Small-Body Database Browser: (2005 HC4)" (2005-05-11 last obs (arc=11 days)). Jet Propulsion Laboratory. Retrieved 30 March 2016.
3. "NEODyS 2005 HC4". Near Earth Objects – Dynamic Site. Retrieved 7 March 2014.
4. As calculated with the vis-viva-equation : ${\displaystyle v^{2}=GM\left({2 \over r}-{1 \over a}\right)}$ where:
   • v is the relative speed of the two bodies
   • r is the distance between the two bodies
   • a is the semi-major axis (a > 0 for ellipses, a = ∞ or 1/a = 0 for parabolas, and a < 0 for hyperbolas)
   • G is the gravitational constant
   • M is the mass of the central body

External links

• 2005 HC4 at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• 2005 HC4 at ESA–space situational awareness
  • Ephemerides · Observations · Orbit · Physical properties · Summary
• 2005 HC4 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters

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