101 Helena

101 Helena
Discovery
Discovered by	James Craig Watson
Discovery date	15 August 1868
Designations
MPC designation	(101) Helena
Pronunciation	/ˈhɛlənə/[1]
Named after	Helen of Troy
Alternative designations
Minor planet category	Main belt
Orbital characteristics[2]
	Epoch 31 July 2016 (JD 2457600.5)
	Uncertainty parameter 0
Observation arc	145.07 yr (52986 d)
Aphelion	2.94606 AU (440.724 Gm)
Perihelion	2.22353 AU (332.635 Gm)
Semi-major axis	2.58480 AU (386.681 Gm)
Eccentricity	0.13977
Orbital period	4.16 yr (1517.9 d)
Average orbital speed	18.44 km/s
Mean anomaly	236.265°
Mean motion	0° 14m 13.823s / day
Inclination	10.1976°
Longitude of ascending node	343.419°
Argument of perihelion	348.030°
Earth MOID	1.21369 AU (181.565 Gm)
Jupiter MOID	2.4117 AU (360.79 Gm)
TJupiter	3.387
Physical characteristics
Dimensions	65.84±1.3 km[2]
Mass	3.0×1017 kg
Mean density	2.0 g/cm³
Equatorial surface gravity	0.0184 m/s²
Equatorial escape velocity	0.0348 km/s
Rotation period	23.080 h (0.9617 d)[2]
Geometric albedo	0.1898±0.008[2]
Temperature	~173 K
Spectral type	S[3]
Absolute magnitude (H)	8.33

Helena (minor planet designation: 101 Helena) is a large, rocky main-belt asteroid. It was discovered by Canadian-American astronomer J. C. Watson on August 15, 1868,[4] and was named after Helen of Troy in Greek mythology.

This object is orbiting the Sun with a period of 4.16 years and an eccentricity of 0.14. Its orbital plane is inclined by 10.2° to the plane of the ecliptic. Radar observations were made of this object on Oct 7 and 19, 2001 from the Arecibo Observatory. Analysis of the data gave an estimated ellipsoidal diameter of 71×63×63 ± 16% km. The mean diameter estimated from IRAS infrared measurements is 66 km, in agreement with the radar findings. It is classified as an S-type asteroid in the Tholen system,[3][5] suggesting a predominantly silicate composition. 101 Helena is spinning on its axis with a period of 23 hours.[2]

References

Noah Webster (1884) A Practical Dictionary of the English Language
Yeomans, Donald K., "101 Helena", JPL Small-Body Database Browser, NASA Jet Propulsion Laboratory, retrieved 12 May 2016.
DeMeo, Francesca E.; et al. (2011), "An extension of the Bus asteroid taxonomy into the near-infrared" (PDF), Icarus, 202 (1): 160–180, Bibcode:2009Icar..202..160D, doi:10.1016/j.icarus.2009.02.005, archived from the original (PDF) on 17 March 2014, retrieved 22 March 2013. See appendix A.
"Numbered Minor Planets 1–5000", Discovery Circumstances, IAU Minor Planet center, retrieved 7 April 2013.
Magri, Christopher; Nolan, Michael C.; Ostro, Steven J.; Giorgini, Jon D. (January 2007), "A radar survey of main-belt asteroids: Arecibo observations of 55 objects during 1999 2003", Icarus, 186 (1), pp. 126–151, Bibcode:2007Icar..186..126M, doi:10.1016/j.icarus.2006.08.018.

External links

101 Helena at AstDyS-2, Asteroids—Dynamic Site
- Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
101 Helena at the JPL Small-Body Database
- Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters

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[1] Noah Webster (1884) A Practical Dictionary of the English Language

[JPL-2] Yeomans, Donald K., "101 Helena", JPL Small-Body Database Browser, NASA Jet Propulsion Laboratory, retrieved 12 May 2016.

[DeMeo2011-3] DeMeo, Francesca E.; et al. (2011), "An extension of the Bus asteroid taxonomy into the near-infrared" (PDF), Icarus, 202 (1): 160–180, Bibcode:2009Icar..202..160D, doi:10.1016/j.icarus.2009.02.005, archived from the original (PDF) on 17 March 2014, retrieved 22 March 2013. See appendix A.

[IAU_MPC-4] "Numbered Minor Planets 1–5000", Discovery Circumstances, IAU Minor Planet center, retrieved 7 April 2013.

[Icarus186-5] Magri, Christopher; Nolan, Michael C.; Ostro, Steven J.; Giorgini, Jon D. (January 2007), "A radar survey of main-belt asteroids: Arecibo observations of 55 objects during 1999 2003", Icarus, 186 (1), pp. 126–151, Bibcode:2007Icar..186..126M, doi:10.1016/j.icarus.2006.08.018.