NASA’s Juno mission is rewriting what planetary researchers thought they knew about Jupiter, the largest and most massive planet in our Solar System: the latest science results from the mission portray the gas giant as a complex, turbulent world, with massive polar cyclones, plunging storm systems, and an extremely strong magnetic field that may indicate it was generated closer to the planet’s surface than previously thought.
Juno made its first scientific close-up, known as a ‘perijove’, on August 27, 2016.
Lasting a few hours, the solar-powered spacecraft flies from the north pole to the south pole, dipping within 2,600 miles (4,200 km) of the equatorial clouds and beneath Jupiter’s most intense and damaging radiation belts.
The findings from the first data-collection pass are being published this week in two papers in the journal Science, as well as 44 papers in the journal Geophysical Research Letters.
“We knew, going in, that Jupiter would throw us some curves,” said Juno principal investigator Dr. Scott Bolton, from the Southwest Research Institute.
“But now that we are here we are finding that Jupiter can throw the heat, as well as knuckleballs and sliders. There is so much going on here that we didn’t expect that we have had to take a step back and begin to rethink of this as a whole new Jupiter.”
“What we’ve learned so far is earth-shattering. Or should I say, Jupiter-shattering,” he added.
Among the findings that challenge assumptions are those provided by Juno’s imager, JunoCam.
The images show both of Jupiter’s poles are covered in Earth-sized swirling storms that are densely clustered and rubbing together.
“We’re puzzled as to how they could be formed, how stable the configuration is, and why Jupiter’s north pole doesn’t look like the south pole,” Dr. Bolton said.
“We’re questioning whether this is a dynamic system, and are we seeing just one stage, and over the next year, we’re going to watch it disappear, or is this a stable configuration and these storms are circulating around one another?”
Also surprising, Jupiter’s signature bands disappear near its poles.
Since the first observations of these belts and zones many years ago, astronomers have wondered how far beneath the gas giant’s swirling façade these features persist.
Juno’s Microwave Radiometer (MWR) reveals that topical weather phenomena extend deep below the cloudtops, to pressures of 100 bars, 100 times Earth’s air pressure at sea level.
“However, there’s a north-south asymmetry. The depths of the bands are distributed unequally,” Dr. Bolton said.
“We’ve observed a narrow ammonia-rich plume at the equator. It resembles a deeper, wider version of the air currents that rise from Earth’s equator and generate the trade winds.”
Prior to the Juno mission, it was known that Jupiter had the most intense magnetic field in the Solar System.
Measurements of the gas giant’s magnetosphere, from Juno’s magnetometer investigation (MAG), indicate that Jupiter’s magnetic field is even stronger than models expected, and more irregular in shape.
“Juno’s gravity field measurements differ significantly from what we expected, which has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter’s core,” Dr. Bolton noted.
The magnitude of the observed magnetic field was 7.766 Gauss, about 10 times stronger than the strongest magnetic field found on Earth, significantly stronger than expected.
But the real surprise was the dramatic spatial variation in the field, which was significantly higher than expected in some locations, and markedly lower in others.
Planetary researchers think a dynamo — a rotating, convecting, electrically conducting fluid in a planet’s outer core — is the mechanism for generating the planetary magnetic fields.
“We characterized the field to estimate the depth of the dynamo region, suggesting that it may occur in a molecular hydrogen layer above the pressure-induced transition to the metallic state,” Dr. Bolton said.
“Juno is giving us a view of the magnetic field close to Jupiter that we’ve never had before,” said Juno deputy principal investigator Dr. Jack Connerney, of NASA’s Goddard Space Flight Center.
Juno also is designed to study the polar magnetosphere and the origin of Jupiter’s powerful auroras.
These auroral emissions are caused by particles that pick up energy, slamming into atmospheric molecules.
Juno’s initial observations indicate that the process seems to work differently at Jupiter than at Earth.
“Although many of the observations have terrestrial analogs, it appears that different processes are at work creating the auroras,” said Juno’s JADE (Jovian Auroral Distributions Experiment) instrument lead Dr. Phil Valek, from the Southwest Research Institute.
“With JADE we’ve observed plasmas upwelling from the upper atmosphere to help populate Jupiter’s magnetosphere.”
“However, the energetic particles associated with Jovian auroras are very different from those that power the most intense auroral emissions at Earth.”
“Jupiter threw an auroral firework party to celebrate Juno’s arrival,” said Dr. Jonathan Nichols, reader in planetary auroras at the University of Leicester.
“We have been able to show that intense pulses of aurora were triggered during intervals when the solar wind was buffeting the giant magnetosphere. This tells us that even Jupiter’s mighty magnetosphere is, like those of Earth and Saturn, not immune to the vagaries of the Sun and the solar wind.”
“The Jovian system is known to contain several icy moons, namely Europa and Ganymede, which may potentially have extraterrestrial life in their underground oceans of liquid water, and the energy driven from the far area toward Jupiter could provide support for chemical processes on the icy surface of the moons,” said Dr. Tomoki Kimura, a special postdoctoral researcher at RIKEN, Japan.
“In the past we did not know how the energy was accelerated to such tremendous velocities, but now, thanks to the new findings, we have a better idea. Now that Juno is in orbit around Jupiter, we will continue to receive new observational data that will help us pin down how the energy is transferred, again allowing us to gain insights in our search for life in those icy worlds.”
“We are excited to share these early discoveries, which help us better understand what makes Jupiter so fascinating,” said Dr. Diane Brown, Juno program executive at NASA Headquarters in Washington.
“It was a long trip to get to Jupiter, but these first results already demonstrate it was well worth the journey.”
S.J. Bolton et al. 2017. Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with the Juno spacecraft. Science 356 (6340): 821-825; doi: 10.1126/science.aal2108
J.E.P. Connerney et al. 2017. Jupiter’s magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits. Science 356 (6340): 826-832; doi: 10.1126/science.aam5928
J.D. Nichols et al. Response of Jupiter’s auroras to conditions in the interplanetary medium as measured by the Hubble Space Telescope and Juno. Geophys. Res. Lett, published online May 25, 2017; doi: 10.1002/2017GL073029
T. Kimura et al. Transient brightening of Jupiter’s aurora observed by the Hisaki satellite and Hubble Space Telescope during approach phase of the Juno spacecraft. Geophys. Res. Lett, published online May 25, 2017; doi: 10.1002/2017GL072912
S.W.H. Cowley et al. Magnetosphere-ionosphere coupling at Jupiter: Expectations for Juno Perijove 1 from a steady state axisymmetric physical model. Geophys. Res. Lett, published online May 25, 2017; doi: 10.1002/2017GL073129