When I was young I read a short story about a creature made of plasma ejected from the sun by a solar flare. It flew through space and hit the boiling hot sun-facing side of Mercury, whereupon it 'froze' to death. It blew my mind. I thought it was from Arthur C Clarke, but I can't seem to find it. Any help would be appreciated.
The story you're describing is "Out of the Sun" by Arthur C Clarke.
We were looking at what seemed to be a translucent oval, its interior laced with a network of almost invisible lines. Where the lines crossed, there appeared to be tiny, pulsing nodes of light; we could never be quite sure of their existence because the radar took almost a minute to paint the complete picture on the screen—and between each sweep the object moved several thousand miles. There was no doubt, however, that the network itself existed; the cameras settled any arguments about that.
Then the radar screen was empty, wiped clean during a single scan of the beam. The creature had fallen below our horizon, and was hidden from us now by the curve of the planet. Far out in the burning dayside of Mercury, in the inferno where only a dozen men have ever ventured and fewer still come back alive, it smashed silently and invisibly against the seas of molten metal, the hills of slowly moving lava. The mere impact could have meant nothing to such an entity what it could not endure was its first contact with the inconceivable cold of solid matter.