NASA, SWRI, MSSS
Scientists are repainting Jupiter’s portrait — scientifically, anyway. NASA’s Juno spacecraft swooped within 5,000 kilometers (3,100 miles) of Jupiter’s cloud tops last August 27. Scientists’ first close-up of the gas giant has unveiled several unexpected details about the planet’s gravity and powerful magnetic fields. They also give a new view of the planet’s auroras and ammonia-rich weather systems.
Researchers need to revamp their view of Jupiter, these findings suggest. They even challenge ideas about how solar systems form and evolve. The findings come from two papers published May 26 in Science.
“We went in with a preconceived notion of how Jupiter worked,” says Scott Bolton. “And I would say we have to eat some humble pie.” Bolton is a planetary scientist who leads the Juno mission. He works at the Southwest Research Institute in San Antonio, Texas.
Scientists thought that beneath its thick clouds, Jupiter would be uniform and boring. Not anymore. “Jupiter is much more complex deep down than anyone anticipated," Bolton now observes.
One early surprise came from Jupiter’s gravity. Juno measured that gravity from its tug on the spacecraft. The values suggest that Jupiter doesn’t have a solid, compact core. Instead, the core is probably large and diffuse. It could even be as big as half the planet’s radius, Bolton and his colleagues conclude. “Nobody anticipated that,” Bolton notes.
Imke de Pater is a planetary scientist. She works at the University of California, Berkeley and was not involved in the new studies. The new gravity measurements should lead to a better understanding of the planet’s core, she says. But, she adds, doing so will require using some challenging math.
She was more surprised by Jupiter’s magnetic field. It is the strongest of any planet in our solar system. And Juno’s data show that it is almost twice as strong as expected in some spots. Its strength varies. It gets stronger than expected in some areas, weaker in others. These data support the idea that this magnetic field originates from circulating electric currents. Those currents are probably in one of the planet’s outer layers of hydrogen.
Responding to the ‘wind’
A second study looked at how Jupiter’s magnetic field interacts with a stream of charged particles flowing from the sun. Known as the solar wind, these particles affects Jupiter’s auroras, points out John Connerney. An astrophysicist, he led this study with colleagues at NASA’s Goddard Space Flight Center in Greenbelt, Md.
Auroras are brilliant shows of colored light that appear at or near a planet's poles. (Earth’s auroras are known as the Northern and Southern Lights.) Juno captured Jupiter’s auroras in ultraviolet and infrared light. These images come from wavelengths beyond what the human eye can see. They showed particles falling into the planet’s atmosphere. That is similar to what happens on Earth. But they also showed beams of electrons shooting out from Jupiter’s atmosphere. Nothing like that occurs on Earth.
Bolton’s team described another oddity. Ammonia wells up from the depths of Jupiter’s atmosphere in a strange way. This upwelling resembles a feature on Earth called a Hadley cell. Warm air at our equator rises and creates trade winds, hurricanes and other forms of weather. Jupiter’s ammonia cycling looks similar to this. But Jupiter lacks a solid surface, the researchers note. So the upwelling likely works in a completely different way than on Earth. The scientists hope to figure out how this works on Jupiter. This could help scientists better understand the atmospheres of such huge gas planets.
Explains Bolton, Jupiter is a standard of comparison for all gas giants — both within and beyond our solar system. Most planetary systems have Jupiter-like planets. He says that means researchers can apply what they learn about Jupiter to giant planets elsewhere.
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ammonia A colorless gas with a nasty smell. Ammonia is a compound made from the elements nitrogen and hydrogen. It is used to make food and applied to farm fields as a fertilizer. Secreted by the kidneys, ammonia gives urine its characteristic odor. The chemical also occurs in the atmosphere and throughout the universe.
atmosphere The envelope of gases surrounding Earth or another planet.
aurora A light display in the sky caused when incoming energetic particles from the sun collide with gas molecules in a planet’s upper atmosphere. The best known of these is Earth’s aurora borealis, or northern lights. On some outer gas planets, like Jupiter and Saturn, the combination of a fast rate of rotation and strong magnetic field leads to high electrical currents in the upper atmosphere, above the planets’ poles. This, too, can cause auroral “light” shows in their upper atmosphere.
colleague Someone who works with another; a co-worker or team member.
core Something — usually round-shaped — in the center of an object. (in geology) Earth’s innermost layer. Or, a long, tube-like sample drilled down into ice, soil or rock. Cores allow scientists to examine layers of sediment, dissolved chemicals, rock and fossils to see how the environment at one location changed through hundreds to thousands of years or more.
current A fluid — such as of water or air — that moves in a recognizable direction. (in electricity) The flow of electricity or the amount of electricity moving through some point over a particular period of time.
diffuse Spread out thinly over a great area; not concise or concentrated.
electric current A flow of electric charge — electricity — usually from the movement of negatively charged particles, called electrons.
electron A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.
equator An imaginary line around Earth that divides Earth into the Northern and Southern Hemispheres.
evolve (adj. evolving) To change gradually over generations, or a long period of time, in living organisms. Nonliving things also may be described as evolving if they change over time.
field (in physics) A region in space where certain physical effects operate, such as magnetism (created by a magnetic field), gravity (by a gravitational field), mass (by a Higgs field) or electricity (by an electrical field).
gas giant A giant planet that is made mostly of the gases helium and hydrogen. Jupiter and Saturn are gas giants.
gravity The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
hurricane A tropical cyclone that occurs in the Atlantic Ocean and has winds of 119 kilometers (74 miles) per hour or greater. When such a storm occurs in the Pacific Ocean, people refer to it as a typhoon.
hydrogen The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues.
infrared light A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means “below red.” Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X-rays, radio waves and microwaves. Infrared light tends to record the heat signature of an object or environment.
Jupiter (in astronomy) The solar system’s largest planet, it has the shortest day length (10 hours). A gas giant, its low density indicates that this planet is composed of light elements, such as hydrogen and helium. This planet also releases more heat than it receives from the sun as gravity compresses its mass (and slowly shrinks the planet).
magnetic field An area of influence created by certain materials, called magnets, or by the movement of electric charges.
NASA Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It has also sent research craft to study planets and other celestial objects in our solar system.
particle A minute amount of something.
phenomenon Something that is surprising or unusual.
planet A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood. To accomplish the third feat, the object must be big enough to have pulled neighboring objects into the planet itself or to have slung them around the planet and off into outer space.
radius A straight line from the center to the circumference of a circle or sphere.
solar system The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.
solar wind A flow of charged particles (including atomic nuclei) that have been ejected from the surface of the star, such as our sun. It can permeate the solar system. This is called a stellar wind, when from a star other than the sun.
spectrum (plural: spectra) A range of related things that appear in some order. (in light and energy) The range of electromagnetic radiation types; they span from gamma rays to X rays, ultraviolet light, visible light, infrared energy, microwaves and radio waves.
sun The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.
ultraviolet A portion of the light spectrum that is close to violet but invisible to the human eye.
upwelling The process by which material rises from Earth’s middle layer into its outer layer, where it will become part of the tectonic plates.
wavelength The distance between one peak and the next in a series of waves, or the distance between one trough and the next. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.
weather Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.
Journal: S.J. Bolton et al. Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with the Juno spacecraft. Science. Vol. 356, May 26, 2017, p. 821. doi: 10.1126/science.aal2108.
Journal: J.E.P. Connerney et al. Jupiter’s magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits. Science. Vol. 356, May 26, 2017, p. 826. doi: 10.1126/science.aam5928.