I know I've had a fair few of these questions recently, but I just can't remember their titles!

So, this one kind of reminded me of 2001: A Space Odyssey. It has aliens that left a special artifact on the moon which broadcasts signals into space. Then, something happens that causes those signals to stop and people go to investigate, I think. It was also once mentioned that the aliens used special human technology to put the artifact there. Final detail: I'm pretty sure the object was in the shape of a pyramid or a triangular prism. 60% sure that this is Asimov, Bradbury, or one of the other Sci-Fi giants.


You may be thinking of The Sentinel, a short story by Arthur C. Clarke.

The alien artifact in that story was a translucent Tetrahedron, which matches your description.

This short story provided the inspiration for a rather well known film.

  • The plot description in the question is kinda the inverse of Sentinel. My first thought as well, though. – Organic Marble May 1 '19 at 21:20
  • This is absolutely right! I didn't know it was the inspiration for A Space Odyssey. I just thought they were kinda similar. – user112267 May 1 '19 at 23:49