Hey, Alexa, how many trips to Mars can you buy with a billion bucks?

Amazon CEO Jeff Bezos might be musing over that question this weekend, after selling more than $1 billion worth of stock in his company on Friday.

The sale came to light as the result of a filing with the US Securities and Exchange Commission.

Amazon's stock shot up a breathtaking 13 percent on the previous Friday -- Oct. 27 -- after the company easily bested its third-quarter earnings expectations. That popped Bezos into the world's-richest-man slot, knocking out Microsoft co-founder and noted philanthropist Bill Gates. It was a return visit for Bezos; he'd briefly held the No. 1 spot back in July.

It's not clear what Bezos will do with the money from the stock sale, but in April he did say he likes to sell shares to fund his spaceship project.

"My business model right now ... for Blue Origin is I sell about $1 billion of Amazon stock a year and I use it to invest in Blue Origin," Bezos said at the annual Space Symposium in Colorado, according to Bloomberg.