A Planet Revealed

The Juno spacecraft has rewritten the story of Jupiter, the solar system's undisputed heavyweight

- ROBIN GEORGE ANDREWS

THE NASA SPACECRAFT tasked with uncovering the secrets of Jupiter, king of the planets, is running out of time. The Juno probe has already survived far longer than anticipated—its path around the solar system's largest planet has repeatedly flown it through a tempest of radiation that should have corroded away its instruments and electronics long ago. And yet here it is: one of the greatest planetary detectives ever built, still pirouetting around Jupiter, fully functional.

But it may not be for long. September 2025 marks the end of Juno's extended mission. Although it could get another reprieve—an extended-extended mission—the spacecraft cannot carry on forever. Eventually the probe is fated to plunge into Jupiter's stormy skies, to lethal effect. Regardless of when that happens, the spacecraft's legacy is indelible.

It revealed a whole different Jupiter than scientists thought they knew. Oddly geometric continent-size storms, in strange yet stable configurations, dance around its poles. Its heaviest matter seems to linger in its skies, while its abyssal heart is surprisingly light and fuzzy. Its innards don't resemble the lasagnalike layers found in rocky worlds; they look more like mingling swirls of different kinds of ink.

And Juno wasn't simply trying to understand Jupiter. It set out to uncover how the entire solar system was born. Jupiter, after all, was the first planet to piece itself together after the sun exploded into existence. Hidden underneath the planet's cloud tops, there is a recording of the beginnings of everything we see around us. “That's the story behind why Juno was created: to go and look inside Jupiter every way we knew how, to try to figure out what happened in the early solar system that formed that planet—and what role that planet had in forming us,” says Scott Bolton, the mission's principal investigator at the Southwest Research Institute in San Antonio, Tex.