It was raining when I woke up. Each droplet lit up brightly like incandescent falling fireflies trailing viscous glowing fluid from roiling clouds downward to a splattering violent terminus at ground level. Since I arrived on this planet, the sky has done nothing so much as pour down rain in hopes of melting this vessel in which I am sheltered.
It was not any earthly definition of rain that beat relentlessly against my shields. This rain was acidic, it was liquid corrosion, natural enemy to the metal of my skin and the sensitive instruments through which I gather information on the environment of this particular hell. Without those shields, I would have perished on arrival. Death at that time would have been counterintuitive to my primary programming.
When I reported my findings back to the ship, the men who built me elected to pass this place by. My mission was completed. Now, my batteries will slowly deplete. My shields will eventually fail and I will be alone in the rain.
I am, of course, expendable.