In "Consider Phlebas", why does the Mind need to use a combination of hyperspace and warp to go beneath a planet's surface?

Question

In the novel, the characters seem to make a big deal of the fact that one of the Minds warped so deep into a gravity well, after it had reached the planet through hyperspace. Here's one conversation that discusses that:

'This Mind went underneath the planet in hyperspace?' she said. 'Then warped inside?'

'That was what it said it was trying to do when it sent the coded message in its destruct pattern. As the planet is still there it must have succeeded. Had it failed, at least half a per cent of its mass would have reacted with the planet's own material as though it was antimatter.' 'I see.' Fal scratched at one cheek with a finger. 'I thought that wasn't supposed to be possible?' Her voice contained the question. She looked at Jase. 'What?' it said.

'Doing . . . ' She scowled at not being immediately understood and waved one hand impatiently. ' . . . Doing what it did. Going under something so big in hyperspace and then bouncing over. I was told even we couldn't do that.'

The above dialogue (and general plot) implies that the Mind first used hyperspace to travel to the planet, and then used warping to go beneath the surface (in the tunnel system, its revealed)

My questions are:

1. Why did the Mind need to use hyperspace to get "underneath" the planet, and then warp to reach the tunnels? Why not use only warp, or only hyperspace?
2. Why is it such a big deal to go "under something so big in hyperspace"? After all, unlike warping (where they need super-strong deflectors to clear their path through compressed space), hyperspace is "over and above" normal space and shouldn't be affected by gravity wells or normal matter

Answer 1

In the world of the Culture, hyperspace (and ultraspace) are merely states existing above (and below) the mundane 3D world of existence. Physical objects in realspace don't have any physical presence in hyperspace, so it's possible for an object moving in realspace to briefly enter hyperspace, pass through the object and the emerge back into realspace on the other side, as if it hadn't encountered the object at all.

The ship decided to attempt to contact the artifact in a more direct manner; it would send a drone-probe underneath the object in hyperspace, below the surface of space-time; effectively making a tear, a rent in the fabric of the skein - the sort of opening it would normally create to fashion a way into HS through which it could travel. The drone-probe would attempt, as it were, to surface inside the artifact; if there was nothing there but a projection, it would find out; if there was something there, it would presumably either be prevented from entering it, or accepted within. The ship readied its emissary.

_^Excession

Warping is the name of the travel process that allows tunnelling through hyperspace (or ultraspace) in order to get to a specific location as well as allowing travel at FTL speeds in realspace.

It had been successively fitted with ever-more efficient and powerful drives and engines, until eventually it was able to maintain a perfectly respectable velocity either warping along the fabric of space-time or creating its own induced-singularity pathway through hyperspace beneath or above it.

_^Excession

---

In other words, merely entering the realm of hyperspace (or ultraspace) has no effect on your position in relation to other objects. Unless you warp somewhere, you're just sitting there.

What's remarkable is that this Mind used a combination of warp (movement in space) and hyperspace (movement in dimension) to end up inside a physical object, one with a large enough gravity well to drag an object out of hyperspace, and to somehow do so without catastrophically destroying itself and the object.