Beyond his interests in Amazon and The Washington Post, the newly-minted world’s richest man owns the Blue Origin rocket company. It’s a passion project for Bezos—one to which he has pledged $1 billion in Amazon stock each year. He even teased construction of the company’s first rocket manufacturing plant in his first Instagram post.

He’s hardly alone. At least four other billionaires are hoping to explore the stars. Here’s a look at their efforts.

Mark Zuckerberg

The Facebook founder (and world’s fifth richest person) wants to see what secrets the galaxy holds. Teaming with scientist Stephen Hawking and Russian venture capitalist Yuri Milner, he has helped fund The Starshot Project, an ambitious attempt to send miniature robots to the far reaches of space, including Alpha Centauri. The 25 million mile trip to Alpha Centauri would normally take 30,000 years, but Starshot thinks it can make the journey in 20.

Paul Allen

Allen, the co-founder of Microsoft and world’s 45th richest, runs Vulcan Aerospace, which is working on building a 238-foot-long jet aircraft (with a wingspan of 385 feet) that will take rockets to a high altitude before they separate and climb into orbit, letting them launch in any kind of weather—without a launch pad.

Elon Musk

He ranks 67 on the Forbes list, but Musk is front and center in the private space industry. As CEO and CTO of SpaceX, he has a crew of roughly 5,000 people working toward his goal of being the first to send a vessel to Mars.

Richard Branson

Branson’s down at 361 on the list, with a $5.1 billion net worth, but he has long been an advocate of space tourism. Virgin Galactic suffered a setback two years ago when its spacecraft came apart during a test flight, but tests will resume this year and the company hopes to begin commercial flights in 2018.