2005 HC4

2005 HC₄ is the asteroid with the second-smallest perihelion and the asteroid with the smallest known perihelion of any known object orbiting the Sun from 2005 to 2024 (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).^[4] Since then, another asteroid, 2024 YL3, has been found to have a closer perihelion, at about 0.070 AU.^[5] 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^[6] (there are comets, however, which obtain much higher speeds).

DiscoveredbyLONEOS

Discoverydate30 April 2005

Minorplanet category

• Mercury Crosser
• Venus Crosser
• Apollo Asteroid
• Mars Crosser

Aphelion3.5707 AU (534.17 Gm)

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2005 HC₄

Discovery[1]
Discovered by	LONEOS
Discovery date	30 April 2005
Designations
Minor planet category	Mercury Crosser Venus Crosser Apollo Asteroid Mars Crosser
Orbital characteristics[2]
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° 24m 4.32s /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[3]
Absolute magnitude (H)	20.7

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