Tesla (TSLA) and SpaceX CEO Elon Musk was slammed on Twitter for a tweet he sent out on Sunday that said OCCUPY MARS with a picture that he believed was Mars.

In reality, Musk had just tweeted out a picture of a "blood moon" taken during a total lunar eclipse in July 2018. In response, Twitter users pointed out that "that's the moon" and sent memes and photoshopped pictures at his expense.

Musk was lighthearted about the incident, sending out laughing emojis and tweeting they would occupy the "moon too."

Musk currently leads the Space Exploration Technologies Corporation initiative, also known as Space X. One of the main goals of the initiative is to colonize Mars. According to SpaceX's website, the company wants to send its first cargo mission to Mars in 2022.

How soon would it be possible to colonize Mars? In an interview with PBS, Jim Pawelcysk, a former astronaut and professor at Penn State University, said that while small outposts on the red planet are possible, it's likely a century away that full-scale settlements could be built there.

Yet concerns have been raised whether it is ethical to colonize Mars. Forbes reported that human colonization of the red planet could disturb life forms or biological processes there.

In the meantime, Musk tweeted that he will likely send SpaceX's signature model Starship to the moon first over Mars as "it’s only 3 days away" and "doesn't need interorbital synchronization."