An average of 500m of water if distributed over the surface of Mars is at the upper limit of what I recall being estimated previously. I think the range was either 100-500m or 200-500m. The news would be in confirming the most optimistic estimate and in having a reliable measure since past estimates required a lot of educated guessing. While they may have turned out right, they could have been far off. A lot less water would have been bad news for the chances of Martian life and human colonization.

It's not surprising news just really good news if the 500m estimate is correct.

Regards,
Mark Eby