2017-05-25 14:16:03
NASA Spacecraft Finds a Chaotic Dance of Storms at Jupiter’s Poles

14:16, May 25 621 0

The top and bottom of Jupiter are pockmarked with a chaotic mélange of swirls that are actually immense storms hundreds of miles across. The planet’s interior core appears bigger than expected, 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 plumes of ammonia may be rising out of the planet.

Those are some of the early findings of scientists working on NASA’s Juno mission, an orbiter that arrived at Jupiter on July 4 last year. With a looping elliptical orbit, Juno is making repeated dives to within about 2,600 miles of the cloud tops. The spacecrafts’ instruments peer far beneath, giving scientists glimpses of the inside of Jupiter, the solar system’s largest planet.

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.

NASA’s earlier missions — the flybys of Voyager 1 and 2 in 1979 and an extended orbital visit by Galileo from 1995 to 2003 — looked at Jupiter from the side. What the spacecraft could see of the polar regions was from a sharp angle, with details hard to make out.

“You never really see the whole thing in all its glory at the same time,” said John E.P. Connerney, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., and deputy principal investigator on the mission.

With Juno’s orbits passing almost directly over the north and south poles, scientists now have a much better view.

That enables a much closer study of the powerful auroras, which are generated by charged particles traveling along Jupiter’s magnetic field. At Earth, charged particles from the sun speeding outward through the solar system are diverted by the planet’s magnetic field and slam into the ground in the polar regions. The expectation was that the same would be occurring at Jupiter.

Because Juno is not only looking at the auroras from above but also traveling through the magnetic fields and charged particles that generate the auroras, the scientists were able to see that the charged particles — mostly electrons — were traveling in the opposite direction at Jupiter: out of the planet into space. “That would be a complete 180 degree reversal of our thinking,” Dr. Connerney said.

He said the outflow of electrons, while unanticipated, actually fit with observations from the Voyager flybys.

The magnetic field is also not as uniform as expected. “We find the spatial variations in the magnetic field that are intriguing,” Dr. Connerney said. “We see the field is stronger in magnitude than we expected in some places, much weaker than we expected in other places.”

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, the planet’s prime constituent, which turns into a metallic fluid under crushing pressures.

For the magnetic field 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 a 53-day orbit instead. The spacecraft is to make the same number of orbits and collect the same amount of data.

The longer mission means that Juno may be able to detect slow changes in the magnetic field. “That would be intriguing as well,” Dr. Connerney said.

The chaotic pattern of storms detected by Juno is also a surprise. 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 a result of a change of seasons from winter to summer.

In the final stages of the Cassini mission, which ends in September, the spacecraft has shifted to a looping elliptical orbit, which will enable similar probing of Saturn’s interior.