I've done some blasting in my day, and know that explosives -- even very large ones -- which are placed on the surface of a rock don't do much except move dust around*. Sometimes they create a bit of spalling, but often they won't even fracture the rock. It's just too easy for the energy of the explosion to dissipate in the air. At the very least, you need to use a shaped explosive charge which is either bolted in place or nailed to the surface via a lot of kinetic energy (which is how bunker-busting bombs work). Far preferable to that, is to drill a hole and place the explosives inside it. But in this case, if you can drill a hole, then your job is already accomplished.

Anyhow, drilling isn't that hard. Had the Beagle 2 survived, its "Mole" could have gotten to a depth of 6 feet -- a lot better than any explosive you'd consider carrying could do.

Cheers,

Nthan.

* And on Mars, explosives wouldn't even do that, given the low density of the atmosphere. Most of the dust-moving gasses would have to come from the explosive itself, which wouldn't be very much.