Orbital elements:
Elliptic orbit (ell_orbit):
1.	orbit_Epoch (default: J2000)
2.	orbit_Eccentricity
3.
	orbit_PericenterDistance
	or
	orbit_SemiMajorAxis
4.
	orbit_MeanMotion
	or
	orbit_Period
	or
	skip both
5.	orbit_Inclination
6.	orbit_AscendingNod
7.
	orbit_ArgOfPericenter
	or
	orbit_LongOfPericenter
8.
	orbit_MeanAnomaly
	or
	orbit_MeanLongitude
	
Comet orbit (comet_orbit):
1.	orbit_Eccentricity
2.
	orbit_PericenterDistance
	or
	orbit_SemiMajorAxis
3.	
	orbit_MeanMotion (degrees/day)
	or
	orbit_Period (days ???)
	or
	skip both if the parent is the Sun
4.
	orbit_TimeAtPericenter (JD)
	or
	(orbit_Epoch (JD)
	and
	orbit_MeanAnomaly (degrees))
5.	orbit_Inclination (degrees)
6.	orbit_ArgOfPericenter (degrees)
7.	orbit_AscendingNode (degrees)

Planet properties:
*	parent
*	lighting (bool)
*	radius
*	oblateness (default: 0.)
*	color (RGB, decimal fractions of 1)
*	albedo
*	tex_map (filename)
*	hidden (bool, default: 0 ???)
*	atmosphere (bool, default: false)

Rotation elements:
*	rot_obliquity (d: 0.)
*	rot_equator_ascending_node (d: 0.)
*	rot_pole_ra (default: 0.)
	and/or
	rot_pole_de (default: 0.)
	(if any of these are !=0, rot_obliquity and rot_equator_ascending_node are
	recalculated)
*	rot_periode (default: orbit_Period (default: 24.) / 24., i.e. default: 1.)
*	rot_rotation_offset (default: 0.)
*	rot_epoch (default: J2000)
*	rot_precession_rate (default: 0.)
*	orbit_visualization_period (default: 0.)

Rings (if any):
*	ring_inner_size (internally: in AU)
*	ring_outer_size (ditto)
*	tex_ring (filename)