11.  But they did find huge river canyons, proof that bone-dry Mars once had liquid water.

12.  But this is the first time that liquid water has actually made it to Earth.

13.  But two kilometers under the Martian surface, say some scientists, is liquid water at a temperature capable of sustaining life.

14.  Earth is the only planet in the solar system known to have liquid water on its surface.

15.  Earth remains the only place in the solar system with liquid water in plain view.

16.  Find liquid water on Mars, and life may not be far behind.

17.  If blocks of ice have tilted so their thickness can be estimated, the pictures could even show how far down the liquid water lies.

18.  If the analysis also produces chemical signatures of minerals typically formed in liquid water, then scientists will gain even more evidence that Mars once was much more hospitable.

19.  If so, Europa would be the first place in the solar system other than Earth where liquid water is known to be abundant.

20.  If so, it is more likely that the heat and liquid water that shaped Europa in the past are still active there.