Downey stoked hype about the announcement in a cryptic video message posted to Twitter on Thursday, in which he told followers he was “bubbling with anticipation.”
He teased the announcement with a riddle: “What do the Rolling Stones, NASA, the Rose Bowl and the ruling planet of my birth sign all have in common?” he said.
The video has been watched more than 2.3 million times, and it ignited a flurry of speculation in the comments section.
“NASA is building a football stadium on Mars and hosting the Rose Bowl with the Stones performing the halftime show!” one person wrote.
“A rock concert with a real life Iron Man suit?” asked another.
Downey took the stage on Thursday night ahead of the Stones’ performance at the Rose Bowl in Pasadena, Calif., to announce that NASA had named a Mars rock after the band.
Scientists at NASA spotted the rock tumbling across the surface of Mars through their InSight lander robot last November.
It was — quite literally — a rolling stone, so the scientists decided to give it that name “in a fit of fandom and clever association,” Downey said.
“Cross-pollinating science and a legendary rock band is always a good thing,” the actor said backstage.
The Rolling Stones thanked NASA for the honour after they took the stage for their set.
“NASA has given us something we have always dreamed of, our very own rock on Mars. I can’t believe it,” Mick Jagger told the crowd. ″I want to bring it back and put it on our mantlepiece.”
The InSight lander was actually responsible for moving the rock with the force of its thrusters, NASA said. The rock was slightly bigger than a golf ball and it tumbled approximately 0.9 metres — farther than NASA has seen any other rock roll when landing on another world.
WATCH: NASA successfully lands InSight on Mars in November 2018
“I’ve seen a lot of Mars rocks over my career,” Matt Golombek, a JPL geologist who has helped NASA land all its Mars missions since 1997, said in a statement. “This one probably won’t be in a lot of scientific papers, but it’s definitely one of the coolest.”
Downey hailed the discovery in a tweet Thursday night. “Sometimes the world does seriously cool stuff,” he wrote.
Twitter users were conflicted once the crossover details were revealed.
“I was hoping for aliens,” user David A. Oliver wrote.
“Strange collab but I’ll take it,” said user @starktowr.
Several mourned the loss of Downey’s character, Tony Stark, by echoing his final words in Avengers: Endgame.
“We love you 3,000!” they wrote.