Re: "How much more proof do they need?"
[If the hydrogen component in ALH84001 is magmatic, this would imply that hydrous magma with a low activity of water may have existed in the Martian mantle ~4.5 Gyr ago. Alternative, the hydrogen signature may represent an interaction of ALH84001 with crustal fluids that equilibrated with a primitive atmosphere that was much less fractionated than the present day Martian atmosphere.]
From: http://www.lpi.usra.edu/meetings/metsoc98/pdf/5275.pdf
---
Note the "~4.5 Gyr ago". I think they need actual proof from present day Mars: Core samples would be nice.
Marcia