Can you take a guarded step in difficult terrain

Question

So the way I am reading the rules it seems impossible to take a guarded step in Starfinder in difficult terrain.

So the guarded step rules say:-

You can carefully step 5 feet as a move action. This movement doesn’t provoke attacks of opportunity (see page 248), even if you’re in a threatened square (see page 255).

And the difficult terrain rules say:-

Difficult terrain, such as heavy undergrowth, piles of junk, or steep stairs, hampers movement. Each move into a square of difficult terrain counts as 2 squares of movement. Each diagonal move into a difficult terrain square counts as 3 squares. You can’t run or charge across difficult terrain. If you occupy multiple squares with different kinds of terrain, you can move only as fast as the most difficult terrain will allow. Flying and incorporeal creatures are not hampered by most difficult terrain, though a dense tree canopy or web of chains might count as difficult terrain for flying creatures.

Answer 1

No

Although the rules interaction isn't explicit, the two rules combine together. Difficult terrain doubles the cost of moving into the terrain. Therefore, a 5' move is not enough to crawl into it. The Crawl move action also gives 5' of movement, and would similarly not allow one to crawl into a square of difficult terrain.

Under Movement and Position is a section entitled Minimum Movement

Despite whatever penalties to your speed you might have, as long as you can move at all you can take a full action to move 5 feet (1 square) in any direction, even diagonally. >This rule doesn’t allow you to move through impassable terrain or to move when all movement is prohibited. Such movement provokes attacks of opportunity as normal (despite the distance covered, this move isn’t a guarded step).

This and Crawl demonstrate that not all 5' movements are Guarded Steps.

Answer 2

It's not made explicit, but it's confirmed by other rules.

As you yourself quoted in the question, the guarded step rules text does not say anything about difficult terrain. It only says that you can move 5 feet as a move action, while the difficult terrain rules say that it takes two squares of movement to move into a square of difficult terrain. Since a guarded step is one square's worth of movement, it appears you can't use it to go into difficult terrain.

This is confirmed indirectly by the presence of the Nimble Moves feat.

You can move through up to 20 feet of difficult terrain each round as if it were normal terrain. This feat allows you to take a guarded step into difficult terrain.