Jupiter does not sit still. Its atmosphere races around the planet in more than 20 east-west jet streams, with winds reaching about 100 meters per second, more than three times faster than the strongest jet stream on Earth. Those bands of motion, visible in the planet’s bright stripes and turbulent storms, have been watched for centuries. But only recently have scientists begun to pin down how far those winds reach and what keeps them going inside the solar system’s largest planet. That question matters because Jupiter is not just a bigger Earth. It has no solid surface, rotates in about 10 hours, and is made mostly of a relatively uniform mix of gases. In some ways that makes it simpler to study. In other ways, it makes the planet harder to understand, because the atmosphere blends into the deep interior. Recent measurements and computer models now point to a picture that is both clearer and stranger. Jupiter’s jet streams do not stay near the cloud tops. They plunge thousands of kilometers downward, into regions where …