if you want rough answer not taking into account non-spherosity of the planet on the large scale nor the curvature of the planet on the small scale i would think something like this might be close enough.

• break your distance into EW and NS components.
• find circumference of planetoid. --> c
• your loc = x,y (longitude,latitude)
• find circumference at original latitude. --> c' = c * cos(y); (c' = c at equator; c' = 0 at 90deg)
• x' = x +- ( c' / 360 ) * EW
• y' = y +- ( c / 360 ) * NS

be carefull near the poles!

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