I'm not sure if this question would be considered for "advanced" users or not,
but: Is it possible to cast caustics from an object without seeing things
reflected in its surface?

I am modeling a planet, and I would like to see reflected light illuminating the
dark side of one of its moons. I briefly tried radiosity, but photon mapping
seemed more accurate.

My problem is that I don't want to see objects reflected in the surface of the
planet; I only want the caustics it casts. ...Is this outright impossible?

Below is a boiled-down version of my scene code.
Thanks, God bless!

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#local sun_radius      =   40.00; // units in meters*10^6
#local plan_orbt_rdus  = 3000.00; // planet's orbit radius
#local aphelion_offset =   20.00; // distance of ephelion from otherwise
circular orbit
#local plan_radius     =    6.53;
#local plan_moon_dist  =    6.00; // dist @ closest point between moon's
surfaces
#local plan_moon_rdus  =    6.22; // moon radius
#local plan_rotn_prod  =    4.70; // rotation period in hours
#local camr_dist       =    3.00; // multiplier for camera dist
#local plan_poso = radians(073);  // planet's orbital position in radians
counterclockwise from positive x axis
#local plan_day  = 0;             // planet's rotational position in hours - one
full turn every multiple of 4.70

#local plan_moon_posr = plan_radius+plan_moon_dist+plan_moon_rdus;
#local plan_rotn = (plan_day/4.7)*-360-degrees(plan_poso);
#local plan_posx =
cos(plan_poso)*(plan_orbt_rdus+aphelion_offset*0.5)-aphelion_offset*0.5;
#local plan_posz = sin(plan_poso)*plan_orbt_rdus;

camera
 {
 location <0,1,-0.1>*(plan_moon_posr+plan_moon_rdus)*(camr_dist+1.0) look_at 0
 right x*image_width/image_height
 rotate <0,plan_rotn,0>
 translate <plan_posx,0,plan_posz>
 angle 48
 }
light_source {<-10,0.1,0> color rgb 1 photons {reflection on}}

global_settings
 {
 ambient_light 0
 max_trace_level 15
 photons {count 100000 spacing 10}
 }

#local plan_color = <0.3,0.7,1>;
union
 {
 sphere {0,plan_radius hollow texture {pigment {rgb plan_color} finish
{reflection plan_color*20}} photons {target reflection on collect off}}
 sphere {<plan_moon_posr,0,0>,plan_moon_rdus texture {pigment {rgb plan_color}}
photons {target} rotate <0,150,0>}
 translate <plan_posx,0,plan_posz>
 }

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