Explore "Message From Mars" by Clifford D. Simak on Textopian. Read with annotations and highlights.
The Martians hadn't wanted them to to come. That much, at least, was clear. But having gotten here, the Martians had no intention of letting them return to Earth again. They didn't want them to carry back the word that it was possible to navigate across space to the outer planet.
Maybe the Martians were committed to a policy of isolation. Maybe there was a "Hands Off" sign set up on Mars. Maybe a "No trespassing" sign.