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This chart presents data that the Waves investigation on NASA’s Juno spacecraft recorded as the spacecraft crossed the bow shock just outside of Jupiter’s magnetosphere on June 24, 2016, while approaching Jupiter. Audio accompanies the animation, with volume and pitch correlated to the amplitude and frequency of the recorded waves.
The graph is a frequency-time spectrogram with color coding to indicate wave amplitudes as a function of wave frequency (vertical axis, in hertz) and time (horizontal axis, with a total elapsed time of two hours). During the hour before Juno reached the bow shock, the Waves instrument was detecting mainly plasma oscillations just below 10,000 hertz (10 kilohertz). The frequency of these oscillations is related to the local density of electrons; the data yield an estimate of approximately one electron per cubic centimeter (about 16 per cubic inch) in this region just outside Jupiter’s bow shock.
The broadband burst of noise marked “Bow Shock” is the region of turbulence where the supersonic solar wind is heated and slowed by encountering the Jovian magnetosphere. The shock is analogous to a sonic boom generated in Earth’s atmosphere by a supersonic aircraft. The region after the shock is called the magnetosheath.
The vertical bar to the right of the chart indicates the color coding of wave amplitude, in decibels (dB) above the background level detected by the Waves instrument. Each step of 10 decibels marks a tenfold increase in wave power.
When Juno collected these data, the distance from the spacecraft to Jupiter was about 5.56 million miles (8.95 million kilometers), indicated on the chart as 128 times the radius of Jupiter. Jupiter’s magnetic field is tilted about 10 degrees from the planet’s axis of rotation. The note of 22 degrees on the chart indicates that at the time these data were recorded, the spacecraft was 22 degrees north of the magnetic-field equator. The “LT” notation is local time on Jupiter at the longitude of the planet directly below the spacecraft, with a value of 6.2 indicating approximately dawn.
The University of Iowa, Iowa City, provided Juno’s Waves instrument. NASA’s Jet Propulsion Laboratory, Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. The Juno mission is part of the New Frontiers Program managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama. Lockheed Martin Space Systems, Denver, built the spacecraft. JPL is a division of Caltech in Pasadena.
Image credit: NASA/JPL-Caltech/SwRI/Univ. of Iowa
NASA’s Juno Spacecraft Enters Jupiter’s Magnetic Field
NASA’s Jupiter-bound Juno spacecraft has entered the planet’s magnetosphere, where the movement of particles in space is controlled by what’s going on inside Jupiter.
“We’ve just crossed the boundary into Jupiter’s home turf,” said Juno Principal Investigator Scott Bolton of Southwest Research Institute, San Antonio. “We’re closing in fast on the planet itself and already gaining valuable data.”
Juno is on course to swing into orbit around Jupiter on July 4. Science instruments on board detected changes in the particles and fields around the spacecraft as it passed from an environment dominated by the interplanetary solar wind into Jupiter’s magnetosphere. Data from Juno’s Waves investigation, presented as audio stream and color animation, indicate the spacecraft’s crossing of the bow shock just outside the magnetosphere on June 24 and the transit into the lower density of the Jovian magnetosphere on June 25.
“The bow shock is analogous to a sonic boom,” said William Kurth of the University of Iowa in Iowa City, lead co-investigator for the Waves investigation. “The solar wind blows past all the planets at a speed of about a million miles per hour, and where it hits an obstacle, there’s all this turbulence.”
The obstacle is Jupiter’s magnetosphere, which is the largest structure in the solar system.
“If Jupiter’s magnetosphere glowed in visible light, it would be twice the size of the full moon as seen from Earth,” Kurth said. And that’s the shorter dimension of the teardrop-shaped structure; the dimension extending outward behind Jupiter has a length about five times the distance between Earth and the sun.
Out in the solar wind a few days ago, Juno was speeding through an environment that has about 16 particles per cubic inch (one per cubic centimeter). Once it crossed into the magnetosphere, the density was about a hundredfold less. The density is expected to climb again, inside the magnetosphere, as the spacecraft gets closer to Jupiter itself. The motions of these particles traveling under the control of Jupiter’s magnetic field will be one type of evidence Juno examines for clues about Jupiter’s deep interior.
While this transition from the solar wind into the magnetosphere was predicted to occur at some point in time, the structure of the boundary between those two regions proved to be unexpectedly complex, with different instruments reporting unusual signatures both before and after the nominal crossing.
“This unusual boundary structure will itself be the subject of scientific investigation,” said Barry Mauk of the Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, who is the instrument lead for the Jupiter Energetic-Particle Detector Instrument (JEDI) on Juno.
The Juno spacecraft launched on Aug. 5, 2011, from Cape Canaveral, Florida.
NASA’s Jet Propulsion Laboratory, Pasadena, California, manages the Juno mission for Principal Investigator Bolton. 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. Lockheed Martin Space Systems, Denver, built the spacecraft. Caltech, in Pasadena, manages JPL for NASA.
source : NASA – Jet Propulsion Laboratory – California Institute of Technology