NASA's Juno mission has already surpassed all possible expectations. When it arrived on Jupiter last July after a five-year voyage, the probe became the farthest solar-powered object from Earth and also flew faster than any other object created by humans. The probe's flight path is closer to the thunderous gas giant than any other craft that has been there before. And this is the first spacecraft that will pass by the mysterious poles of Jupiter and find out, contrary to most assumptions, that they are blue and do not have stripes characteristic of the planet.
Last August, Juno flew over Jupiter and collected data that scientists have been decrypting since. Two papers have been published today on the subject of Jupiter's auroras, atmosphere, magnetic and gravitational fields. Jupiter's atmospheric dynamics are not only less than thought to resemble those of Earth, they are much more complex and changeable. To fully understand Jupiter, a single probe may not be enough. Fortunately, Juno is doing a good job.
It's worth starting with the upper atmosphere and Jupiter's auroras. Scientists already knew that Jupiter's aurora borealis make our familiar northern lights a dull twinkle: they are hundreds of times more energetic and cover a larger area than the entire planet Earth. Juno uses several instruments to study the energetic particles of these auroras and the physics that govern their dynamics. And if the data from the first approach allows us to draw certain conclusions, the auroras of Jupiter are very different from those on Earth.
“I really want to interpret what I saw on another planet based on Earth,” says Jack Connerney, astrophysicist at the Space Flight Center. Goddard at NASA. "Until last week, in our models of Jupiter's auroras, electrons were going in the wrong direction."
On Earth, the electrons of the planet's magnetic field are excited by the solar wind, and then sent to the poles, where they fly into other atoms and molecules, emitting a characteristic glow. On Jupiter, the Juno instruments have discovered that electrons are actually excited as they leave the polar regions.
On top of that, all indications are that planetary scientists generally misjudged Jupiter's atmospheric dynamics.
"Scientists believed that the sun would be the primary source of energy in the atmosphere," says Scott Bolton, Juno's principal investigator and lead author of another paper. "So they assumed that once we got below the sunlight, the particles would be simple and easy to see."
But everything turned out not to be so: the particles of Jupiter's atmosphere are as varied and lined as the famous striped appearance of the planet. Of particular interest is the equatorial ammonia belt, which extends hundreds of kilometers down to the planet's core - as far as the Juno instrument could see. Based on the most current models of the atmosphere of Jupiter, this should not be so at all.
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The deep layers of Jupiter's atmosphere were especially active: the magnetic and gravitational fields that the probe plans to map.
“If Jupiter were just a large and spinning ball of gas, there shouldn't be any strange harmonics in its gravitational field,” says Connerney. But Jupiter's gravity is not uniform, which may indicate deep convection - drops deep in Jupiter can lead to gravitational fluctuations in the same way that changes in atmospheric pressure change the weather on Earth. Jupiter's magnetic field also turned out to be more changeable geographically than scientists expected.
Juno's team still does not understand why Jupiter's atmosphere is so disorganized, although Connerney dares to suggest that all fluctuations may be associated with deep convection, expressed in the gravitational field, which also leads to an uneven magnetic field. “In hindsight, we wonder why we thought it was going to be simple and boring,” says Bolton.
A detailed understanding of Jupiter's atmosphere could help scientists understand some of Earth's strangest features. Bolton compares Jupiter's equatorial ammonia to the tropical zone around Earth's own equator. “The concept we have on Earth is that the streak evolves because the air has an ocean to bounce off of,” says Bolton. “But Jupiter doesn't, so why does everything look the same there? Perhaps we do not understand something fundamental about the atmosphere. Perhaps our assumptions about the Earth were wrong."
The same transfer of information can be applied to the Earth's magnetic field, which is difficult to study because it is generated deep beneath the earth's crust and is partially obscured by random deposits of iron. Jupiter has no crust and no additional magnets to collect data. This is the first time we have the opportunity to look at a real magnetic dynamo. Maybe we should have started with Jupiter.
All of these discoveries challenge our understanding of space - and not just because of the results. Typically, scientists first send a probe to the planet, followed by an orbiter equipped with all the data gadgets the probe will collect. Our idea of how Jupiter and the giant planets work, which has emerged over the past few decades, was too simple.
And that means we need more missions in the style of "Juno" - with more orbits, which will allow us to make a complete map of the planet. Lucky this probe did its job. It's only the beginning.
ILYA KHEL