[RightWhale]

We all probably know what's going on, but we can't walk into that room since the doorways are so low. No clearance, you'll hit your head.

[Joe Hadenuf]

The radar sounder on board Mars Express, MARSIS, will map the subsurface structure from a depth of about a hundred metres to as much as a few kilometres. This is in contrast with the Mars Odyssey, which can sense surface compositions to a depth of only one metre.

Now this data will prove to be interesting.