Need to pinpoint the source of my laptop's overheating that led to physical melting of the touchpad

Alienware M17x R3 (released in 2011)

I opened my laptop lid to find strange marks that looked as though an interior piece of the laptop overheated and melted the exterior. The melted area is near the touchpad. The left click button was also affected - it doesnt click properly anymore.

I tued it on and immediately noticed that the area around the touchpad began to get hotter. I quickly tued off the laptop after touching the touchpad and noticing it begin to grow hotter (I didn't want to risk anymore damage).

I opened the laptop and looked at what was directly under the melted but I don't know what to make of it. Here are some pictures of the damage and what is undeeath.

What could be causing this? What would I need to replace? Someone suggested to me that it might be the processor overheating because the laptop is 5 years old. However, the processor is not undeeath the affected area, but the battery is. But when I removed the battery after quickly tuing it off, the battery was not abnormally hot.

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