Armageddon

The film opens on depicting the CretaceousâPaleogene extinction event caused by a collision of an asteroid striking the Earth 65 million years ago, with narration warning that such an event will happen again.
In the present day, a massive meteor shower destroys the orbiting Space Shuttle Atlantis and bombards a swath of land from the U.S. East Coast to Europe, particularly in New York City. NASA discovers through the Hubble that the meteors were debris propelled from the asteroid belt by a rogue asteroid roughly the size of Texas. The asteroid will collide with Earth in 18 days, causing another extinction event. NASA scientists, led by Dan Truman, plan to trigger a thermonuclear detonation at least 800 feet (240Â m) inside the asteroid to split it in two, driving the pieces apart so both will fly past the Earth. NASA contacts Harry Stamper, considered the best deep-sea oil driller in the world, for assistance. Harry insists he will need his full team to help execute NASA's plan, and they agree to help but only after their list of unusual rewards are met.
NASA plans to launch two specialized shuttles, Freedom and Independence, to increase the chances of success; the shuttles will refill with liquid oxygen from a Russian space station before making a slingshot maneuver around the Moon to approach the asteroid from behind. NASA puts Harry and his crew through a short and rigorous astronaut training program, while Harry's team re-outfit the mobile drillers, "Armadillos", for the job. During training, Truman and Harry question the abilities of A.J. Frost, a hot-headed drill operator who has also been dating Harry's daughter Grace against Harry's wishes.
The destruction of Shanghai by a meteorite forces NASA and the military to reveal the asteroid's existence, as well as their plan. The shuttles are launched and arrive at the space station, where its sole cosmonaut Lev Andropov helps with refueling. A major fire breaks out during the fueling process, forcing the crews, including Lev, to evacuate in the shuttles before the station explodes. The shuttles perform the slingshot around the Moon, but approaching the asteroid, the Independence's engines are destroyed by trailing debris, and it crashes on the asteroid. Grace, aware A.J. was aboard the Independence, is traumatized by this news. Unknown to the others, A.J., Lev, and "Bear" (another of Harry's crew) survive the impact and head towards the Freedom target site in their Armadillo.
Freedom safely lands on the asteroid, but overshoots the target zone, landing on a much harder metallic field than planned, and their drilling quickly falls behind schedule. The military initiates "Secondary Protocol", planning to remotely detonate the weapon at the asteroid's surface, despite Truman and Harry's insistence that it would be ineffective. Truman delays the military, while Harry convinces the shuttle commander Colonel Willie Sharp to disarm the remote trigger. Harry's crew continues to work, but in their haste, they accidentally hit a gas pocket, blowing their Armadillo into space and losing another man. As the world learns of the mission's apparent failure, another meteorite devastates most of Paris.
All seems lost until Independence's Armadillo arrives. With A.J. at the controls, they reach the required depth for the bomb. However, flying debris from the asteroid damages the triggering device, requiring someone to stay behind to manually detonate the bomb. The crew draw straws, and A.J. is selected. As he and Harry exit the airlock, Harry rips off A.J.'s air hose and shoves him back inside, telling him that he is the son Harry never had and gives his blessing to marry Grace. Harry contacts Grace to bid his final farewell. After some last minute difficulties involving both the shuttle engines and the detonator, the Freedom moves to a safe distance and Harry triggers the detontation, experiencing visions of Grace in his final moments. The bomb successfully splits the asteroid, avoiding the collision with Earth. Freedom safely returns to Earth, and the surviving crew are treated as heroes. A.J. and Grace get married, with photos of Harry and the other lost crew members present.

Question: What does Harry's crew accidentally hit while drilling?
Answer: a gas pocket