Not really. The polar caps are almost certainly CO2. That's why they completely disappear in summer, despite temps that we'd consider subarctic.
We think there may still be subsurface water. We certainly hope so. But "know" is too strong a word.
Just burn that bible
2015/16 -17- Kirkwood days
Arbor A-Frame 158 2009-10
Jeremy Jones Hovercraft 156, 2011/12
Subaru WRX 06 - 181K