• MPC Preparation (Info)

  • Perturbing Bodies

    Files of perturbed orbital elements maintained by the Minor Planet Center now specifically code the source of the planetary ephemerides and any additional perturbing bodies to the major planets Mercury to Neptune.

    The following description details the changes in the one-line format used for submitting orbits to the Minor Planet Center. Columns 1-201 and 210-220 of this one-line format are not affected by the description below. This additional information is included in orbits extracted via the Extended Computer Service but, for simplicity, not in the printed MPCs.

    Column 202 contains a descriptor of the system used for the perturbing planets according to the follow scheme:

         (space)    Undefined/unknown, assume JPL DE200 positions + masses
            d       JPL DE200 positions + masses
            f       JPL DE245 positions + masses
            h       JPL DE403 positions + masses
            j       JPL DE405 positions + masses
            k       JPL DE431 positions + masses
            l       JPL DE441 positions + masses
    Computers wishing to use other systems should apply to the Minor Planet Center for a descriptor. Note that new codes will only be assigned under exceptional circumstances. Consistency in the perturbation schemes used is more important than changing the scheme with every minor update of the JPL ephemerides.

    The coarse indication of perturbing bodies is given in columns 204-206. Note that minor planets are now indicated by lower-case letters. This allows a distinction to be made between M-P (considering Pluto) and M-p (considering Pallas, and probably Ceres as well).

    The precise indicator of perturbers is given in columns 208-209 as a two-digit hexadecimal number as described below.

               Perturber  Bit  Value
               Hygiea      0     1
    Lo-digit   Earth       1     2       Lo-digit bits 1 + 2 must
               Moon        2     4       both be set or both be
               Ceres       3     8       unset!
    Hi-digit   Pallas      0     1
               Vesta       1     2
               Eunomia     2     4
    Sum the values of the included perturbers and convert to hexadecimal. Since orbits will always include the major planets Mercury to Neptune there is no need to include these bodies in the above scheme (other than allowing the earth and moon to be treated separately).

    Some examples of coarse and precise indicators are:

       Coarse   Precise    Perturbers (Mercury-Neptune+...)
         M-c      08       Ceres, EM barycenter
         M-c      0E       Ceres, Earth, Moon
         M-p      16       Pallas, Earth, Moon    [NOT RECOMMENDED]
         M-p      18       Ceres, Pallas, EM barycenter
         M-p      1E       Ceres, Pallas, Earth, Moon
         M-v      38       Ceres, Pallas, Vesta, EM barycenter
         M-v      3E       Ceres, Pallas, Vesta, Earth, Moon
         M-e      78       Ceres, Pallas, Vesta, Eunomia, EM barycenter
         M-e      7E       Ceres, Pallas, Vesta, Eunomia, Earth, Moon
         M-h      39       Ceres, Pallas, Vesta, Hygiea, EM barycenter
    The default for Minor Planet Center orbits will henceforth be k (DE431), M-v (coarse) and 38 or 3E (precise, depending on whether the object is an earth-approacher or not). Additional perturbers will be added as necessary.