After you acquire the Morph Ball ability from the green E.M.M.I., you find a teleportal back to Artaria.
Get a Missile Tank
When you arrive in Artaria, go downward from the Teleportal and kill the floating creatures and ceiling creatures. Below that, there are two tunnels in the water. Go to the left side and shoot into the tunnel with a missile. Then you can roll into the tunnel to get a Missile Tank.
Get an Energy Part
Go through the door on the left to reach a Save Room. Then go through the left door. Jump up into the tunnel and roll to the end to get an Energy Part.
Activate a Device
Go upward from there and you will find another tunnel at the upper right. Roll through it. In the next room, make your way through the tunnel while avoiding the creatures that come out of the walls. In the next room, go upward to the upper left of the area. Roll through the tunnel there to reach the next room.
Go upward and there will be a door with a green cover on the right, and a charge beam door above that. Shoot the upper door with a charged shot to open it, then go through.
Go to the right to find a device. Stand on the glowing panel in front of it to activate it.
Escape the Heat
Extreme heat is now rising upward from the bottom of the room, so you need to quickly escape. Go to the left and jump up onto the ledge, then jump up to the right onto the ledge there. Some of the structure will collapse. Go to the right, and jump up to the next ledge. Shoot the block in the wall to the left and roll through the tunnel there. The machinery on the left will rise upward. Slide left through two tunnels, then grab the blue wall on the left and climb to the top. Shoot toward the right to get rid of the blocks at the top of the right wall, and roll through the tunnel that you revealed. Go right and jump upward from there, and keep going to the right. The machinery beneath you will move. Shoot toward the right to get rid of the blocks in your way, or just slide through. Go to the right and jump onto the ledge, then jump onto the ledge to the left. If you go toward the left, some flames will start shooting upward, blocking your path, but the bridge to the right will collapse, so go to the right, then jump up onto the next ledge. It will collapse under you, so jump up and shoot at the wall to break open a tunnel. Roll through, then go to the left while avoiding the flames, then jump up onto the ledge on the left and slide through the tunnel at the end. The extreme heat will be blocked behind you, so you no longer need to run away from it.
Get an Item Sphere
Go upward and shoot through the ceiling to reach the door with the Missile Cover on it. Shoot the red cover with a missile, then open the door and go through.
Go to the right until you can jump up into the tunnel at the end. Shoot the sphere that the statue is holding, then take the item that is revealed. You will get the Varia Suit. You are now safe from extreme heat, but are not safe from extreme cold or lava. Your Dash Melee will now be more powerful.
Return to the Teleportal
Go to the right and slide back through the tunnel, the shoot a charged shot at the door on the right and go through. Go to the right and shoot the floor on the right side of the room to break it open. Then go to the left and shoot a charged shot at the door to open it. Go through.
Go to the left, then fall down below to where there is a slope. At the bottom, slide through the tunnel on the left, then turn right and roll through the tunnel. Continue along the straightforward path to reach a door at the bottom right. Shoot it with a charged shot and go through.
Go to the right and drop down below, then go left and shoot a charged shot at the door and go through.
Go to the left and fall downward. You will land on an Energy Recharge Station. The Teleportal to Cataris is here, and the path below is blocked, so you have to use the Teleportal to return to Cataris.