   By default,  geocentric orbital elements are shown in the J2000
equatorial frame.  Any other sort of elements (heliocentric,
barycentric, centered on other planets or their satellites) is
shown in the J2000 ecliptic frame.  That default will almost
always be what's desired.

   However,  you can select a particular frame to be used for
all elements,  including a 'body frame' element.  These are
elements referred to the current orientation of the central body,
and are sometimes used for inner satellites of other planets.
(Elements for more distant,  'irregular' satellites of the gas
giants are more commonly referenced to the J2000 ecliptic.)

   The frame used will be shown in the orbital elements.  It
makes a significant difference in the inclination,  ascending
node,  and longitude of periapsis;  it makes no difference at
all in the mean anomaly,  semimajor axis,  orbital period,
or eccentricity.
