Author Topic: NASA - Juno - Updates  (Read 174490 times)

Offline Star One

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Re: NASA - Juno - Updates
« Reply #580 on: 06/07/2018 08:39 PM »
Juno Solves 39-Year Old Mystery of Jupiter Lightning

Ever since NASA's Voyager 1 spacecraft flew past Jupiter in March, 1979, scientists have wondered about the origin of Jupiter's lightning. That encounter confirmed the existence of Jovian lightning, which had been theorized for centuries. But when the venerable explorer hurtled by, the data showed that the lightning-associated radio signals didn't match the details of the radio signals produced by lightning here at Earth.

In a new paper published in Nature today, scientists from NASA's Juno mission describe the ways in which lightning on Jupiter is actually analogous to Earth's lightning. Although, in some ways, the two types of lightning are polar opposites.

"No matter what planet you're on, lightning bolts act like radio transmitters -- sending out radio waves when they flash across a sky," said Shannon Brown of NASA's Jet Propulsion Laboratory in Pasadena, California, a Juno scientist and lead author of the paper. "But until Juno, all the lightning signals recorded by spacecraft [Voyagers 1 and 2, Galileo, Cassini] were limited to either visual detections or from the kilohertz range of the radio spectrum, despite a search for signals in the megahertz range. Many theories were offered up to explain it, but no one theory could ever get traction as the answer."

Enter Juno, which has been orbiting Jupiter since July 4, 2016. Among its suite of highly sensitive instruments is the Microwave Radiometer Instrument (MWR), which records emissions from the gas giant across a wide spectrum of frequencies.

"In the data from our first eight flybys, Juno's MWR detected 377 lightning discharges," said Brown. "They were recorded in the megahertz as well as gigahertz range, which is what you can find with terrestrial lightning emissions. We think the reason we are the only ones who can see it is because Juno is flying closer to the lighting than ever before, and we are searching at a radio frequency that passes easily through Jupiter's ionosphere."

While the revelation showed how Jupiter lightning is similar to Earth's, the new paper also notes that where these lightning bolts flash on each planet is actually quite different.

"Jupiter lightning distribution is inside out relative to Earth," said Brown. "There is a lot of activity near Jupiter's poles but none near the equator. You can ask anybody who lives in the tropics -- this doesn't hold true for our planet."

Why do lightning bolts congregate near the equator on Earth and near the poles on Jupiter? Follow the heat.

Earth's derives the vast majority of its heat externally from solar radiation, courtesy of our Sun. Because our equator bears the brunt of this sunshine, warm moist air rises (through convection) more freely there, which fuels towering thunderstorms that produce lightning.

Jupiter's orbit is five times farther from the Sun than Earth's orbit, which means that the giant planet receives 25 times less sunlight than Earth. But even though Jupiter's atmosphere derives the majority of its heat from within the planet itself, this doesn't render the Sun's rays irrelevant. They do provide some warmth, heating up Jupiter's equator more than the poles -- just as they heat up Earth. Scientists believe that this heating at Jupiter's equator is just enough to create stability in the upper atmosphere, inhibiting the rise of warm air from within. The poles, which do not have this upper-level warmth and therefore no atmospheric stability, allow warm gases from Jupiter's interior to rise, driving convection and therefore creating the ingredients for lightning.

"These findings could help to improve our understanding of the composition, circulation and energy flows on Jupiter," said Brown. But another question looms. "Even though we see lightning near both poles, why is it mostly recorded at Jupiter's north pole?"

In a second Juno lightning paper published today in Nature Astronomy, Ivana KolmaöovŠ of the Czech Academy of Sciences, Prague, and colleagues, present the largest database of lightning-generated low-frequency radio emissions around Jupiter (whistlers) to date. The data set of more than 1,600 signals, collected by Juno's Waves instrument, is almost 10 times the number recorded by Voyager 1. Juno detected peak rates of four lightning strikes per second (similar to the rates observed in thunderstorms on Earth) which is six times higher than the peak values detected by Voyager 1.

"These discoveries could only happen with Juno," said Scott Bolton, principal investigator of Juno from the Southwest Research Institute, San Antonio. "Our unique orbit allows our spacecraft to fly closer to Jupiter than any other spacecraft in history, so the signal strength of what the planet is radiating out is a thousand times stronger. Also, our microwave and plasma wave instruments are state-of-the-art, allowing us to pick out even weak lightning signals from the cacophony of radio emissions from Jupiter. "

NASA's Juno spacecraft will make its 13th science flyby over Jupiter's mysterious cloud tops on July 16.

NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA's New Frontiers Program, which is managed at NASA's Marshall Space Flight Center in Huntsville, Alabama, for NASA's Science Mission Directorate. The Microwave Radiometer instrument (MWR) was built by JPL. The Juno Waves instrument was provided by the University of Iowa. Lockheed Martin Space, Denver, built the spacecraft.

More information on Juno can be found at:
« Last Edit: 06/07/2018 11:23 PM by Star One »

Offline RotoSequence

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Re: NASA - Juno - Updates
« Reply #581 on: 09/05/2018 11:03 PM »
Published: 05 September 2018

A complex dynamo inferred from the hemispheric dichotomy of Jupiterís magnetic field

Kimberly M. Moore, Rakesh K. Yadav, Laura Kulowski1, Hao Cao, Jeremy Bloxham, John E. P. Connerney, Stavros Kotsiaros, John L. JÝrgensen, Josť M. G. Merayo, David J. Stevenson, Scott J. Bolton & Steven M. Levin

Nature volume 561, pages 76Ė78 (2018)

Quote from: Abstract
The Juno spacecraft, which is in a polar orbit around Jupiter, is providing direct measurements of the planetís magnetic field close to its surface1. A recent analysis of observations of Jupiterís magnetic field from eight (of the first nine) Juno orbits has provided a spherical-harmonic reference model (JRM09)2 of Jupiterís magnetic field outside the planet. This model is of particular interest for understanding processes in Jupiterís magnetosphere, but to study the field within the planet and thus the dynamo mechanism that is responsible for generating Jupiterís main magnetic field, alternative models are preferred. Here we report maps of the magnetic field at a range of depths within Jupiter. We find that Jupiterís magnetic field is different from all other known planetary magnetic fields. Within Jupiter, most of the flux emerges from the dynamo region in a narrow band in the northern hemisphere, some of which returns through an intense, isolated flux patch near the equator. Elsewhere, the field is much weaker. The non-dipolar part of the field is confined almost entirely to the northern hemisphere, so there the field is strongly non-dipolar and in the southern hemisphere it is predominantly dipolar. We suggest that Jupiterís dynamo, unlike Earthís, does not operate in a thick, homogeneous shell, and we propose that this unexpected field morphology arises from radial variations, possibly including layering, in density or electrical conductivity, or both.

And the obligatory Pop-Sci article:

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Offline Star One

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NASA - Juno - Updates
« Reply #583 on: 11/13/2018 08:09 PM »
Junoís Latest Photo of Jupiter Is Breathtaking

The image, processed from JunoCamís raw data, shows storms and winds in the planetís Northern Temperate Belt
« Last Edit: 11/13/2018 08:10 PM by Star One »

Tags: Jupiter Juno JunoCam