Mercury is a planet with a lot of holes in the ground. The bomb room is located inside of the central cliff.
Watch your step and move around the holes on the first two screens. Walk into the hole with steam coming out of it on the third screen to get launched up to the top of the cliff.
On the top of the cliff is the lever that operates the door to the bomb room. Feel free to flip it, but continue onward.
On the right side of the cliff is a solar power plant, hidden under a large metal hatch. A simple flip of the lever next to the hatch is enough to open the hatch and make the power plant rise. But for now leave the hatch closed and carry on past it.
There is a lever on the right most screen, flip it. Now the power plant will extend its solar panels when out, so flip the lever to open the hatch and raise the power plant.
With that, launch yourself back up on the cliff, flip the lever if you didn't before, and walk to the large door.
Go inside and the bomb is right there in front of you, but the floor is missing. If you set up the solar power plant, simply flipping the lever next to you will raise the floor. Otherwise, go back and check that the power plant is up and has the panels extended.
Disarming the bomb[edit]
With the bomb disarmed note the digit that appears and walk back to the ship.