Bill Gates told the BBC he does not think traveling to Mars is a good use of money.
"You can buy measles vaccines and save lives for $1,000 per life saved," Gates explained.
He also said he thinks Elon Musk has had a positive impact through Tesla even though it's not philanthropic.
Microsoft co-founder Bill Gates said he'd rather pay for life-saving vaccines than spend money going to Mars, commenting on how his priorities differ from one of the other richest men on Earth.
Gates made the comments in an interview with the BBC published Thursday in which journalist Amol Rajan asked the billionaire if he would encourage Tesla founder Elon Musk to join the "club of megaphilantropists," referencing Gates, Warren Buffett, and Jeff Bezos.
"Yeah, I think someday he'll be a great philanthropist," Gates said of Musk. "Obviously things like Tesla are having a positive impact even without being a form of philanthropy. But at the end of the day, I don't think - other than going to Mars a few times, which might cost a little bit - I don't think he'll want to spend it on himself."
Gates added he thinks eventually Musk will become a philanthropist "using his ingenuity."
After a follow-up question from Rajan, Gates also said in his view going to Mars is not a good use of money.
"It's actually quite expensive to go to Mars," he told the BBC. "You can buy measles vaccines and save lives for $1,000 per life saved, and so it just kind of grounds you, as in: 'Don't go to Mars.'"
The Bill & Melinda Gates Foundation, the nonprofit founded by Gates and his ex-wife Melinda French-Gates, has put billions of dollars towards researching, developing, and delivering vaccines to the world's poorest countries. The foundation says it has spent billions on efforts to eradicate polio worldwide, including by expanding access to vaccines.
Gates, along with French-Gates and Buffett, also founded the Giving Pledge, through which some of the world's wealthiest individuals have promised to give away most of their wealth.
Musk, who is often ranked the world's richest person, also signed the pledge in 2012. Last year, Musk made a $5.7 billion charitable donation in Tesla shares to the Musk Foundation, which he launched with his brother, Kimball Musk, in 2002. The foundation distributed about $160 million in 2022, according to Bloomberg.
Musk has previously said it is difficult to find "ways to donate money that really make a difference." In 2021, a Vox report concluded Musk had donated 0.05% of his wealth to charity.
Gates and Musk have publicly disagreed in the past, including on COVID-19, how to address climate change, and space travel.
Musk and the Bill & Melinda Gates Foundation did not immediately respond to Insider's request for comment.