Multiple images combined show Jupiter’s south pole, as seen by NASA’s Juno spacecraft from an altitude of 32,000 miles. The oval features are cyclones. (NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles)

The top and bottom of Jupiter are pockmarked with a chaotic mélange of swirls that are immense storms hundreds of miles across. The planet’s interior core appears bigger than expected, and swirling electric currents are generating surprisingly strong magnetic fields. Auroral lights shining in Jupiter’s polar regions seem to operate in a reverse way to those on Earth. And a belt of ammonia may be rising around the planet’s equator.

Those are some early findings of scientists working on NASA’s Juno mission, an orbiter that arrived at Jupiter last July.

Juno takes 53 days to loop around Jupiter in a highly elliptical orbit, but most of the data gathering occurs in two-hour bursts when it accelerates to 129,000 miles an hour and dives to within about 2,600 miles of the cloud tops. The spacecraft’s instruments peer far beneath, giving glimpses of the inside of the planet, the solar system’s largest.

“We’re seeing a lot of our ideas were incorrect and maybe naïve,” Scott J. Bolton, the principal investigator of the Juno mission, said during a NASA news conference on Thursday.

Two papers, one describing the polar storms, the other examining the magnetic fields and auroras, appear in this week’s issue of the journal Science. A cornucopia of 44 additional papers are being published in the journal Geophysical Research Letters. The papers describe findings based largely on the first two close passes of Jupiter in which Juno was able to make measurements. Juno has now made five, with the next on July 11, when it is to pass directly over the Great Red Spot.

Infrared images and spectra of Jupiter’s thermal emission based on readings from the Jovian Infrared Auroral Mapper aboard the Juno spacecraft. (J.E.P. Connerney et al.)

Scientists are puzzled to see that the familiar striped cloud patterns of Jupiter may be only skin deep. An instrument collecting microwave emissions probes the top layers of the atmosphere, but that data does not reflect what is seen in the clouds. “These zones and belts either don’t exist or this instrument isn’t sensitive to it for some reason,” Dr. Bolton said.

The microwave instrument did detect a band of ammonia rising in the equatorial region from at least a couple of hundred miles down — “the most startling feature that was brand-new and unexpected,” Dr. Bolton said.

In measuring the gravitational field, scientists hoped to learn what lies at the center of Jupiter. Some predicted a rocky core, perhaps the size of Earth or several Earths. Others expected no rocky core, but hydrogen, the planet’s main constituent, all the way down. “Most scientists were in one camp or the other,” Dr. Bolton said, “and what we found is neither is true.” Instead, the data suggests a “fuzzy core,” one that is larger than expected, but without a sharp boundary, perhaps partly dissolved.

The magnetic field is also not simple. “What scientists expected was that Jupiter was relatively boring and uniform inside,” Dr. Bolton said. “What we’re finding is anything but that is the truth.”

John E.P. Connerney, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., and the deputy principal investigator on the mission, reported spatial variations in the magnetic field that were much stronger than expected in some areas and much weaker in others.

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SOURCE: NY Times, Kenneth Chang