I have obtained the hindcast position of Mercury relative to the Sun for the epoch 2000-Jan-01 12:00:00 using two methods: PlanEph ver 4.2 (Dos-based) and JPL Horizons DE431 (online).
The two methods give positions which are over 2000 Km apart.
Details are presented in the following figure:-
I presume that such a large discrepancy is due to some error of specification or understanding on my part. I wonder if anyone can suggest or help me find out what that error might be?
(EDIT)
APPENDIX 1 JPL HORIZONS QUERY SETTINGS
Ephemeris Type:VECTORS
Target Body: Mercury(199)
Coordinate Origin: Sun (body center) [500@10]
Time Span: Start=2000-01-01 11:59, Stop=2000-01-02 12:03,Step=1m
Table Settings: output units=KM-S; CSVformat=YES
Display/Output:download/save(plain text file).
APPENDIX 2 Full listing of the JPL Horizons Output File
(CSV format)
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Revised: Jul 31, 2013 Mercury 199 / 1
GEOPHYSICAL DATA (updated 2008-Feb-07):
Mean radius (km) = 2440(+-1) Density (g cm^-3) = 5.427
Mass (10^23 kg ) = 3.302 Flattening, f =
Volume (x10^10 km^3) = 6.085 Semi-major axis =
Sidereal rot. period = 58.6462 d Rot. Rate (x10^5 s) = 0.124001
Mean solar day = 175.9421 d Polar gravity ms^-2 =
Mom. of Inertia = 0.33 Equ. gravity ms^-2 = 3.701
Core radius (km) = ~1600 Potential Love # k2 =
GM (km^3 s^-2) = 22032.09 Equatorial Radius, Re = 2440 km
GM 1-sigma (km^3 s^-2)= +-0.91 Mass ratio (sun/plnt) = 6023600
Atmos. pressure (bar) = Max. angular diam. = 11.0"
Mean Temperature (K) = Visual mag. V(1,0) = -0.42
Geometric albedo = 0.106 Obliquity to orbit[1] = 2.11' +/- 0.1'
Sidereal orb. per. = 0.2408467 y Mean Orbit vel. km/s = 47.362
Sidereal orb. per. = 87.969257 d Escape vel. km/s = 4.435
Hill's sphere rad. Rp = 94.4 Planetary Solar Const = 9936.9 (Wm^2)
[1] Margot et al., Science 316, 2007
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Ephemeris / WWW_USER Thu Jan 4 09:47:08 2018 Pasadena, USA / Horizons
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Target body name: Mercury (199) {source: DE431mx}
Center body name: Sun (10) {source: DE431mx}
Center-site name: BODY CENTER
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Start time : A.D. 2000-Jan-01 11:59:00.0000 TDB
Stop time : A.D. 2000-Jan-01 12:03:00.0000 TDB
Step-size : 1 minutes
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Center geodetic : 0.00000000,0.00000000,0.0000000 {E-lon(deg),Lat(deg),Alt(km)}
Center cylindric: 0.00000000,0.00000000,0.0000000 {E-lon(deg),Dxy(km),Dz(km)}
Center radii : 696000.0 x 696000.0 x 696000.0 k{Equator, meridian, pole}
Output units : KM-S
Output type : GEOMETRIC cartesian states
Output format : 3 (position, velocity, LT, range, range-rate)
Reference frame : ICRF/J2000.0
Coordinate systm: Ecliptic and Mean Equinox of Reference Epoch
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JDTDB, Calendar Date (TDB), X, Y, Z, VX, VY, VZ, LT, RG, RR,
**************************************************************************************************************************************************************************************************************************************************************************
$$SOE
2451544.999305556, A.D. 2000-Jan-01 11:59:00.0000, -1.946394607859077E+07, -6.691260531388976E+07, -3.679595954330999E+06, 3.699453582609515E+01, -1.116598386942620E+01, -4.307714204076275E+00, 2.327713739463555E+02, 6.978310234741506E+07, 6.152788768051691E-01,
2451545.000000000, A.D. 2000-Jan-01 12:00:00.0000, -1.946172639275932E+07, -6.691327522588462E+07, -3.679854414596554E+06, 3.699499188030234E+01, -1.116441595690670E+01, -4.307627980092747E+00, 2.327714970537363E+02, 6.978313925407939E+07, 6.149432668355465E-01,
2451545.000694444, A.D. 2000-Jan-01 12:01:00.0000, -1.945950667956619E+07, -6.691394504380433E+07, -3.680112869688489E+06, 3.699544788177393E+01, -1.116284803117785E+01, -4.307541750189781E+00, 2.327716200939488E+02, 6.978317614060709E+07, 6.146076565335312E-01,
2451545.001388889, A.D. 2000-Jan-01 12:02:00.0000, -1.945728693901455E+07, -6.691461476764810E+07, -3.680371319606457E+06, 3.699590383050987E+01, -1.116128009224054E+01, -4.307455514367438E+00, 2.327717430669925E+02, 6.978321300699817E+07, 6.142720458993068E-01,
2451545.002083333, A.D. 2000-Jan-01 12:03:00.0000, -1.945506717110758E+07, -6.691528439741514E+07, -3.680629764350098E+06, 3.699635972651007E+01, -1.115971214009566E+01, -4.307369272625786E+00, 2.327718659728678E+02, 6.978324985325259E+07, 6.139364349330478E-01,
$$EOE
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Coordinate system description:
Ecliptic and Mean Equinox of Reference Epoch
Reference epoch: J2000.0
XY-plane: plane of the Earth's orbit at the reference epoch
Note: obliquity of 84381.448 arcseconds wrt ICRF equator (IAU76)
X-axis : out along ascending node of instantaneous plane of the Earth's
orbit and the Earth's mean equator at the reference epoch
Z-axis : perpendicular to the xy-plane in the directional (+ or -) sense
of Earth's north pole at the reference epoch.
Symbol meaning:
JDTDB Julian Day Number, Barycentric Dynamical Time
X X-component of position vector (km)
Y Y-component of position vector (km)
Z Z-component of position vector (km)
VX X-component of velocity vector (km/sec)
VY Y-component of velocity vector (km/sec)
VZ Z-component of velocity vector (km/sec)
LT One-way down-leg Newtonian light-time (sec)
RG Range; distance from coordinate center (km)
RR Range-rate; radial velocity wrt coord. center (km/sec)
Geometric states/elements have no aberrations applied.
Computations by ...
Solar System Dynamics Group, Horizons On-Line Ephemeris System
4800 Oak Grove Drive, Jet Propulsion Laboratory
Pasadena, CA 91109 USA
Information: http://ssd.jpl.nasa.gov/
Connect : telnet://ssd.jpl.nasa.gov:6775 (via browser)
http://ssd.jpl.nasa.gov/?horizons
telnet ssd.jpl.nasa.gov 6775 (via command-line)
Author : [email protected]
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