2) Instead, we'd need to steer a massive asteroid in the Chixculub class to impact that part of mars, and we don't, of course, have that technology yet

"The impactor's estimated size was about 10 km (6 mi) in diameter and may have released an estimated 400 zettajoules (4×10^23 joules) of energy, equivalent to 100 teratons of TNT (10^14 tons), on impact.
By contrast, the most powerful man-made explosive device ever detonated, the Tsar Bomba or Emperor Bomb, had a yield of only 50 megatons, making the Chicxulub impact 2 million times more powerful."
http://en.wikipedia.org/wiki/Chicxulub_crater

So, the impactor that made Chixculub delivered 4×10^23 joules. Campared to the Sun: "The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year"
http://en.wikipedia.org/wiki/Solar_energy
3,850,000 exajoules equals 3.85 x 10^24 which is about ten times more energy than that impactor.
Or about the same energy of a month of Sunlight on Earth.

If a rock vaporizes 10 cubic km of water [ice], that requires:

2.26 * 10^6 Joules per kg to boil
10 cubic km of water is 10^13 kgs
So 2.6 * 10^19 joules or around 1/200,000th
of Sunlight for one year. Or 2 1/2 minutes.

A rock 10 km in diameter with 25% water would
have 130 cubic km of water, so it have to have about
2% water to only have 10 km cubic km of water.