What is a Planetary Decoder? What does it decode? How does it work?

Question

This answer to Classic Space part? says

In White it appears in two Exploriens sets

• 6856: Planetary Decoder

and

• 6982: Explorien Starship

Question: What is a Planetary Decoder? What does it decode? In association with what planets might it be used? And if possible what kinds of signals does it receive and how does it work?

Having just written an answer about optical communications in space the title of the set really piqued my interest!

Answer 1

According to various lego catalogs of 1996 (the set's release year), it's referring to the main play feature of the set :

The two transparent red and blue dishes at the front of the craft can be used to reveal different designs on two included tiles :

• Tile 2 x 2 with Groove with Alien Egg Pattern (Sticker)
• Tile 2 x 2 with Groove with Dinosaur Skeleton and Bone Pattern (Sticker)

One such catalog (1996 Holiday US Shop At Home) gives some more background information :

Transcription :

D. Planetary Decoder

It soars through space, then lands on uncharted planets to search for alien clues! This fully equipped craft has adjustable rocket engines, a rotating telescopic laser, alien clues and decoding equipment. 79 pieces.

#6856 Planetary Decoder $8.75

Cool decoding equipment detects dangerous dinosaurs? Blue screen reveals dino chomping on a bone and red screen reveals dino with mouth wide open.

For some more lore on the Exploriens range of sets, the Bricks 'n Pieces March 1996 issue dedicates some pages to it eg.