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JPL Small-Body Database Browser
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949 Hel (A921 EM)
Classification: Main-belt Asteroid          SPK-ID: 2000949
Ephemeris | Orbit Diagram | Orbital Elements | Mission Design | Physical Parameters | Discovery Circumstances | Close-Approach Data ]

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For accurate long-term ephemerides, please instead use our Horizons system.This orbit viewer was implemented using two-body methods, and hence should not be used for determining accurate long-term trajectories (over several years or decades) or planetary encounter circumstances.


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Orbital Elements at Epoch 2459000.5 (2020-May-31.0) TDB
Reference: JPL 37 (heliocentric ecliptic J2000)
 Element Value Uncertainty (1-sigma)   Units 
e .1922948833195404 3.9026e-08  
a 3.002913050495773 1.4202e-08 au
q 2.425468235831963 1.1617e-07 au
i 10.70139122481058 4.4688e-06 deg
node 321.1674147609966 2.2918e-05 deg
peri 249.5416622901892 2.5498e-05 deg
M 358.2562036839565 1.3445e-05 deg
tp 2459009.706738711291
(2020-Jun-09.20673871)
7.1012e-05 TDB
period 1900.695571822838
5.20
1.3484e-05
3.692e-08
d
yr
n .1894043450918058 1.3437e-09 deg/d
Q 3.580357865159583 1.6933e-08 au
  Orbit Determination Parameters
   # obs. used (total)      2490  
   data-arc span      33361 days (91.34 yr)  
   first obs. used      1928-09-05  
   last obs. used      2020-01-07  
   planetary ephem.      DE431  
   SB-pert. ephem.      SB431-N16  
   condition code      0  
   norm. resid. RMS      .4295  
   source      ORB  
   producer      Otto Matic  
   solution date      2020-Jan-28 17:45:37  

Additional Information
 Earth MOID = 1.44636 au 
 Jupiter MOID = 1.58163 au 
 T_jup = 3.198 
[ hide covariance matrix ]
Orbital Elements at Epoch 2455944.5 (2012-Jan-18.0) TDB
Reference: JPL 37 (heliocentric ecliptic J2000)
 Element Value Uncertainty (1-sigma)   Units 
e .1975785388198468 3.9156e-08  
q 2.405733761012839 1.1712e-07 au
tp 2455205.197266228376
(2010-Jan-08.69726623)
6.2634e-05 TDB
node 321.5437704885084 2.3019e-05 deg
peri 248.7569396328659 2.539e-05 deg
i 10.68655239032148 4.4642e-06 deg
  Orbit Determination Parameters
   # obs. used (total)      2490  
   data-arc span      33361 days (91.34 yr)  
   first obs. used      1928-09-05  
   last obs. used      2020-01-07  
   planetary ephem.      DE431  
   SB-pert. ephem.      SB431-N16  
   condition code      0  
   norm. resid. RMS      .4295  
   source      ORB  
   producer      Otto Matic  
   solution date      2020-Jan-28 17:45:37  

Additional Information
 Jupiter MOID = 1.58163 au 
 T_jup = 3.198 
Orbit Covariance (6×6)
  e q tp node peri i
e 1.53316266507185E-15 -4.565145288475652E-15 -3.191840689696518E-13 -7.891460131682753E-15 -2.953406029422642E-14 -4.810763411055018E-16
q -4.565145288475652E-15 1.371592776139266E-14 9.653197486025642E-13 2.769014367776872E-14 9.370805333888984E-14 2.543816232968578E-15
tp -3.191840689696518E-13 9.653197486025642E-13 3.923046644270075E-9 2.10713219306099E-12 6.947528397025115E-10 2.933152746469204E-12
node -7.891460131682753E-15 2.769014367776872E-14 2.10713219306099E-12 5.29888849737065E-10 -5.19792567703076E-10 8.44373271407457E-12
peri -2.953406029422642E-14 9.370805333888984E-14 6.947528397025115E-10 -5.19792567703076E-10 6.446338934162083E-10 -8.087965917863749E-12
i -4.810763411055018E-16 2.543816232968578E-15 2.933152746469204E-12 8.44373271407457E-12 -8.087965917863749E-12 1.992899519829863E-11

Ephemeris | Orbit Diagram | Orbital Elements | Mission Design | Physical Parameters | Discovery Circumstances | Close-Approach Data ]

Physical Parameter Table
Parameter Symbol Value Units Sigma Reference Notes
absolute magnitude H 9.8   n/a MPO347521  
diameter diameter 63.494 km 0.743 urn:nasa:pds:neowise_diameters_albedos::2.0[mainbelt] (http://adsabs.harvard.edu/abs/2014ApJ...791..121M)  
rotation period rot_per 8.215 h n/a LCDB (Rev. 2019-August); Warner et al., 2009 Result based on less than full coverage, so that the period may be wrong by 30 percent or so.
Published Reference List:
[Brines, P.; Lozano, J.; Rodrigo, O.; Fornas, A.; et al. (2017) Minor Planet Bull. 44, 145-149.]
geometric albedo albedo 0.058   0.013 urn:nasa:pds:neowise_diameters_albedos::2.0[mainbelt] (http://adsabs.harvard.edu/abs/2014ApJ...791..121M)  

949 Hel (A921 EM)          Discovered 1921-Mar-11 by Wolf, M. at Heidelberg
Reference: DISCOVERY.DBLast Updated: 2003-08-29

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Alternate Designations
 A921 EM = 1952 DN = 1954 SN1 
Ephemeris | Orbit Diagram | Orbital Elements | Mission Design | Physical Parameters | Discovery Circumstances | Close-Approach Data ]
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