Wildfire, Book 1 — David Mack

The da Vinci goes on a dangerous salvage mission: to rescue the U.S.S. Orion from a gas giant. As if the turbulent atmosphere of the planet wasn't enough, the Orion is carrying the prototype of the deadly Wildfire device -- a protomatter warhead that can ignite gas giants into stars.
But the operation may be more than even Capt. David Gold's crack team of engineers can handle, as they have to fight against the liquid atmosphere of the planet, the volatility of the Wildfire warhead -- and a strange alien life-form that may be responsible for the attack on the Orion!