Asteroid passes near Earth on September 7. At its closest (18:18 UTC / 2:18 p.m. EDT), it's about the same distance from Earth as weather and communications satellites.
Submit your message on the future of communications or solar system exploration. It might be chosen for a time capsule aboard an asteroid sample return mission.
Tool marks within the engraving suggest that it was likely created by someone who intentionally passed a sharp object again and again over the cave wall.