Water is much more efficient than air at absorbing heat and so even with tiny amounts ofliquid flowing through the system the researchers saw a significant effect.
You also need an appropriate orbit - one that puts you not too close to or far from the heatof the star, one that allows liquid water, which most scientists believe is necessary for life, to exist.
The consequent condensation of the water vapour it is carrying heats the air further (the change of state from gas to liquid sheds latent heat), causing it to continue rising.
Apparently the microwavable pad housed a chemical substance (manufactured by ADEKA) not quite stable enough to handle the heat, sparking a lengthy list ofof cases where the liquid erupted from its container and provided an uncomfortable surprise to the poor soul embracing the creature's volcanic warmth.