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.
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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.
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.
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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.
The
magnetic field is generated by the churning of electrically charged
fluids at the core. On Earth, that comes from the convection of molten
iron in the outer core. On Jupiter, the currents come from hydrogen,
which turns into a metallic fluid under crushing pressures.
The
spatial variations suggest that the dynamo of churning currents is
larger than had been thought and may extend beyond the metallic hydrogen
region, Dr. Connerney said.
For
the magnetic field and gravity measurements, a glitch that has greatly
slowed the pace of data gathering could turn out to be beneficial. A
final engine burn last October was to put Juno in a 14-day orbit, but a
pair of sluggish valves in the fuel system led mission managers to forgo
that, and Juno remains in the 53-day orbit instead. The spacecraft is
to make the same number of orbits and collect the same amount of data,
and the longer mission means that Juno may be able to detect slow
changes in the magnetic field.
More surprises were found at the top and bottom of Jupiter.
With
Juno’s orbits passing almost directly over the north and south poles,
scientists can better study the powerful auroras, which are generated by
charged particles traveling along Jupiter’s magnetic field and
colliding with molecules in the atmosphere. In Earth’s case, charged
particles from the sun speeding outward through the solar system are
diverted by the planet’s magnetic field toward the poles, generating
light when they collide with air molecules. The expectation was that the
same would occur at Jupiter, and it does to some extent.
Interactive Feature: Jupiter and Its Moons
But
Juno also detected charged particles — mostly electrons — traveling in
the opposite direction at Jupiter: out of the planet into space. “It’s a
180-degree turnabout from the way we were thinking about those
emissions,” Dr. Connerney said.
He said a voltage differential in the atmosphere was drawing the electrons upward.
Earlier
photographs of the polar regions were taken from a sharp angle, with
details hard to make out. Juno revealed that the clouds there are very
different from the usual Jupiter stripes. “What you see is incredibly
complex features, the cyclones and anticyclones all over the poles,” Dr.
Bolton said.
Planetary
scientists had wondered whether Jupiter would have a giant hexagonal
pattern like that spotted on Saturn by NASA’s Cassini spacecraft.
On
Wednesday, NASA released new images of Saturn’s north polar region,
which has changed color in the last four years, possibly because summer
has reached the northern hemisphere.
In
the final stages of Cassini’s mission, which ends in September, it has
shifted to a looping elliptical orbit, which will enable similar probing
of Saturn’s interior.
“Eventually
we will compare,” Dr. Bolton said. “We will really be able to advance
our understanding of how these giant planets work.”
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