It was January, the nights chilly and clear, when the astronomer Galileo Galilei made one of his most startling discoveries: The stars he had spotted beside Jupiter were moving. Which meant they were not stars after all, but moons. Which meant that Earth was not the only body that others orbited. Which meant we might not be the center of everything after all.
Four centuries later and an ocean away, on a balmy May evening, I climbed the ladder to the University of Maryland Observatory’s 8-inch refractor telescope and held my breath as that tiger-striped wonder was brought into focus once more.
Galileo was a celebrated physicist and mathematician who opened a new window onto the heavens using a telescope of his own invention. His findings, which he published in a pamphlet called the “Starry Messenger,” would rearrange the solar system and redefine humanity’s place in it. I am just a journalist who barely scraped by in high school physics, and until that spring evening, had never looked through a telescope in my life.
But I like to think that, for Galileo and for me, the effect of seeing another world suspended in our eyepieces was the same: Each of us became vividly, viscerally aware of where we stood in the universe.
That is why Jupiter is my favorite planet. (Other than Earth, of course; but saying Earth is your favorite planet is like saying humanity is your favorite species — pretty self-centered and completely beside the point.) There is something about bearing witness to Jupiter’s massive majesty that makes me feel simultaneously profoundly insignificant and positively grand, aware of space’s vast and chilly expanse, and yet closer to the cosmos than I have ever been.
Jupiter is the planet that puts all of us in our place.
That is not just a metaphor. As the solar system’s biggest planet, it is the most gravitationally powerful. Every other object bends to its influence; even the sun wobbles a bit thanks to Jupiter’s irresistible sway. The planets follow paths that parallel the gas giant’s own tilt, gaps appear in the asteroid belt at places where its influence resonates, and the trajectories of comets are changed as they swoosh past.
Without Jupiter, our home might not even exist. Some astronomers believe that during the solar system’s infancy, 4.6 billion years ago, Jupiter swung through the inner solar system, which was then inhabited by a number of embryonic “super Earths.” The move set off a chain reaction of cataclysmic collisions, at the end of which Jupiter came to rest about half a billion miles from the Sun, tethered by Saturn’s gravity, and the early inner planets were obliterated. Mercury, Venus, Mars and Earth would eventually be born from their wreckage, and some of the water that allowed life to get started on this planet may have been transported to the inner solar system during this tumultuous period.
In the eons since, astronomers long believed, Jupiter has acted as a celestial vacuum cleaner, drawing rogue space rocks away from the inner solar system and shielding us from bombardment. The gas giant seems to bear the brunt of impacts from long-period comets; 25 years ago, scientists watched the fragments of the Shoemaker-Levy comet slam into Jupiter with the force of 6 million megatons of TNT.
But recent studies suggest the story is more complex: Computer simulations found that Jupiter’s disruptive gravity may redirect as many bodies inward as it deflects. Its jostling of bodies in the asteroid belt is thought to have created some of Earth’s most destructive impactors — including the gigantic ball of nickel and iron that created Arizona’s mile-wide Barringer Crater 50,000 years ago.
This seems fitting to me. Jupiter is a Bengal tiger, a Mount Everest, a calving glacier, a Niagara Falls — captivating in its capacity to destroy us, worthy of our awe, admiration and wary respect.
Plus, it is stunning. I mean, seriously, stunning. The images sent back to Earth by NASA’s Juno spacecraft, which has orbited Jupiter since 2016, show a wild impressionist painting of a world. Its poles glimmer with auroras powered by its tremendous magnetic field, and its clouds swirl like celestial latte art. Jupiter’s Great Red Spot, the oldest and biggest storm in the solar system, could swallow Earth whole.
Meanwhile, its moons — all 79 of them — are marvels of their own. Io is the most volcanically active body scientists have seen. Ice-covered Europa is one of their best targets in the search for life beyond Earth. The pockmarks on crater-strewn Callisto are filled with glimmering patches of ice, giving it the appearance of a cosmic disco ball.
Seen through the U-Md. telescope, those moons were mere pinpoints of light. If I had not known better, I would have thought they were stars — much as Galileo assumed when he first saw them 400 years ago.
So I waited an hour, swiveling the telescope toward the cosmos’s other wonders: gleaming red Arcturus, the craggy, mountainous moon. The dusky sky turned to dark velvet as the dome of the stars drifted overhead.
By the time I returned my gaze to Jupiter, the lights of its moons had reorganized. Like us, like the Earth, like everything else in the universe, they still move.