The first lunar base was completed last year. One company, aptly named "Out Of This World Vacations", offers tourists a week-long visit to the Moon. The cost of such a vacation is extremely high.

"It was awesome! Wait till I show you the Moon rocks I brought back," Alex boasted as a crowd gathered around him on the school grounds.

"What's going on here?" Kari whispered to the person beside her.

"Alex is telling us about his experience on the Moon."

"I felt like an Olympian; I was able to jump more than a metre straight up!" The crowd was clearly impressed so Alex continued. "There are no clouds and no light pollution from big cities, so there was an amazing view of the stars. And while you were here, possibly watching the moonrise, I watched the earthrise - right from when it was just visible on the horizon until it was overhead."

"Why should we believe you actually went there?" one sceptic asked.

"I knew there would be doubters, so I brought back a few Moon rocks. I collected these while on a moonwalk in the Sea of Tranquility. Hey, Jack, you collect rocks, this would be a stellar addition to your rock collection! I'm willing to sell you a rock for only..."

"I've heard quite enough," Kari interrupted. "Jack, save your money for your own vacation."

What had Kari heard that indicated the story wasn't true?