Close Encounters of the Jovian Kind: NASA’s Juno to Get a Close Look at Jupiter’s Moon Ganymede

Left to right: The mosaic and geologic maps of Jupiter’s moon Ganymede were assembled incorporating the best available imagery from NASA’s Voyager 1 and 2 spacecraft and NASA’s Galileo spacecraft. Credit: USGS Astrogeology Science Center/Wheaton/NASA/JPL-Caltech

The first of the gas-giant orbiter’s back-to-back flybys will provide a close encounter with the massive moon after over 20 years.

On Monday, June 7, at 1:35 p.m. EDT (10:35 a.m. PDT), NASA’s Juno spacecraft will come within 645 miles (1,038 kilometers) of the surface of Jupiter’s largest moon, Ganymede. The flyby will be the closest a spacecraft has come to the solar system’s largest natural satellite since NASA’s Galileo spacecraft made its penultimate close approach back on May 20, 2000. Along with striking imagery, the solar-powered spacecraft’s flyby will yield insights into the moon’s composition, ionosphere, magnetosphere, and ice shell. Juno’s measurements of the radiation environment near the moon will also benefit future missions to the Jovian system.

Ganymede is bigger than the planet Mercury and is the only moon in the solar system with its own magnetosphere – a bubble-shaped region of charged particles surrounding the celestial body.

“Juno carries a suite of sensitive instruments capable of seeing Ganymede in ways never before possible,” said Juno Principal Investigator Scott Bolton of the Southwest Research Institute in San Antonio. “By flying so close, we will bring the exploration of Ganymede into the 21st century, both complementing future missions with our unique sensors and helping prepare for the next generation of missions to the Jovian system – NASA’s Europa Clipper and ESA’s [European Space Agency’s] JUpiter ICy moons Explorer [JUICE] mission.”

Juno’s science instruments will begin collecting data about three hours before the spacecraft’s closest approach. Along with the Ultraviolet Spectrograph (UVS) and Jovian Infrared Auroral Mapper (JIRAM) instruments, Juno’s Microwave Radiometer’s (MWR) will peer into Ganymede’s water-ice crust, obtaining data on its composition and temperature.


Animation of a rotating globe of Ganymede, with a geologic map superimposed over a global color mosaic. Credit: USGS Astrogeology Science Center/Wheaton/ASU/NASA/JPL-Caltech

“Ganymede’s ice shell has some light and dark regions, suggesting that some areas may be pure ice while other areas contain dirty ice,” said Bolton. “MWR will provide the first in-depth investigation of how the composition and structure of the ice varies with depth, leading to a better understanding of how the ice shell forms and the ongoing processes that resurface the ice over time.” The results will complement those from ESA’s forthcoming JUICE mission, which will look at the ice using radar at different wavelengths when it becomes the first spacecraft to orbit a moon other than Earth’s Moon in 2032.

Signals from Juno’s X-band and Ka-band radio wavelengths will be used to perform a radio occultation experiment to probe the moon’s tenuous ionosphere (the outer layer of an atmosphere where gases are excited by solar radiation to form ions, which have an electrical charge).

“As Juno passes behind Ganymede, radio signals will pass through Ganymede’s ionosphere, causing small changes in the frequency that should be picked up by two antennas at the Deep Space Network’s Canberra complex in Australia,” said Dustin Buccino, a signal analysis engineer for the Juno mission at JPL. “If we can measure this change, we might be able to understand the connection between Ganymede’s ionosphere, its intrinsic magnetic field, and Jupiter’s magnetosphere.”

Three Cameras, Two Jobs

Normally, Juno’s Stellar Reference Unit (SRU) navigation camera is tasked with helping keep the Jupiter orbiter on course, but during the flyby it will do double duty. Along with its navigation duties, the camera – which is well shielded against radiation that could otherwise adversely affect it – will gather information on the high-energy radiation environment in the region near Ganymede by collecting a special set of images.

“The signatures from penetrating high-energy particles in Jupiter’s extreme radiation environment appear as dots, squiggles, and streaks in the images – like static on a television screen. We extract these radiation-induced noise signatures from SRU images to obtain diagnostic snapshots of the radiation levels encountered by Juno,” said Heidi Becker, Juno’s radiation monitoring lead at JPL.

Meanwhile, the Advanced Stellar Compass camera, built at the Technical University of Denmark, will count very energetic electrons that penetrate its shielding with a measurement every quarter of a second.

Also being enlisted is the JunoCam imager. Conceived to bring the excitement and beauty of Jupiter exploration to the public, the camera has provided an abundance of useful science as well during the mission’s almost five-year tenure at Jupiter. For the Ganymede flyby, JunoCam will collect images at a resolution equivalent to the best from Voyager and Galileo. The Juno science team will scour the images, comparing them to those from previous missions, looking for changes in surface features that might have occurred over four-plus decades. Any changes to crater distribution on the surface could help astronomers better understand the current population of objects that impact moons in the outer solar system.

Due to the speed of the flyby, the icy moon will – from JunoCam’s viewpoint – go from being a point of light to a viewable disk then back to a point of light in about 25 minutes. So that’s just enough time for five images.

“Things usually happen pretty quick in the world of flybys, and we have two back-to-back next week. So literally every second counts,” said Juno Mission Manager Matt Johnson of JPL. “On Monday, we are going to race past Ganymede at almost 12 miles per second (19 kilometers per second). Less than 24 hours later we’re performing our 33rd science pass of Jupiter – screaming low over the cloud tops, at about 36 miles per second (58 kilometers per second). It is going to be a wild ride.”

More About the Mission

JPL, a division of Caltech in Pasadena, California, manages the Juno mission for the principal investigator, Scott J. 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 the agency’s Science Mission Directorate in Washington. Lockheed Martin Space in Denver built and operates the spacecraft.

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  • Babu G. Ranganathan

    Babu G. Ranganathan*
    (B.A. Bible/Biology)

    JUST BECAUSE SCIENCE CAN EXPLAIN how an airplane works doesn’t mean that no one designed or made the airplane. And just because science can explain how life or the universe works doesn’t mean there was no Designer and Maker behind them.

    Natural laws may explain how the order in the universe works and operates, but mere undirected natural laws cannot explain the origin of that order. Once you have a complete and living cell then the genetic code and biological machinery exist to direct the formation of more cells from raw materials such as amino acids and other chemicals, but how could life or the cell have naturally originated when no directing code and mechanisms existed in nature? Read my Internet article: HOW FORENSIC SCIENCE REFUTES ATHEISM.

    WHAT IS SCIENCE? Science simply is knowledge based on observation. No human observed the universe coming by chance or by design, by creation or by evolution. These are positions of faith. The issue is which faith the scientific evidence best supports.

    SCIENCE SHOWS THAT THE UNIVERSE CANNOT BE ETERNAL because it could not have sustained itself eternally due to the law of entropy (increasing and irreversible net energy decay, even in an open system). Even a hypothetical oscillating universe could not continue to oscillate eternally! Einstein’s General Theory of Relativity shows that space, matter, and time all are physical and all had a beginning. Space even produces particles because it’s actually something, not nothing. What about the Higgs boson (the so-called “God Particle”)? The Higgs boson, even if it existed, would not have created mass from nothing, but rather it would have converted energy into mass. Einstein showed that all matter is some form of energy. Even time had a beginning! Time is not eternal.

    The law of entropy doesn’t allow the universe to be eternal. If the universe were eternal, everything, including time (which modern science has shown is as physical as mass and space), would have become totally entropied by now and the entire universe would have ended in a uniform heat death a long, long time ago. The fact that this hasn’t happened already is powerful evidence for a beginning to the universe.

    Popular atheistic scientist Stephen Hawking admits that the universe had a beginning and came from nothing but he believes that nothing became something by a natural process yet to be discovered. That’s not rational thinking at all, and it also would be making the effect greater than its cause to say that nothing created something. The beginning had to be of supernatural origin because science teaches us from the First Law of Thermodynamics that natural laws and processes do not have the ability to bring something into existence from nothing.

    The supernatural origin of the universe cannot be proved by science but science points to a supernatural intelligence and power for the origin and order of the universe. Where did God come from? Obviously, unlike the universe, God’s nature doesn’t require a beginning.

    The disorder in the universe can be explained because of chance and random processes, but the order can be explained only because of intelligence and design.

    Gravity may explain how the order found in the precise and orderly courses of thousands of billions of stars is maintained, but gravity cannot explain the origin of that order.

    Some evolutionary astronomers believe that trillions of stars crashed into each other leaving surviving stars to find precise orderly orbits in space. Not only is this irrational, but if there was such a mass collision of stars then there would be a super mass residue of gas clouds in space to support this hypothesis. The present level of residue of gas clouds in space doesn’t support the magnitude of star deaths required for such a hypothesis. And, as already stated, the origin of stars cannot be explained by the Big Bang because of the reasons mentioned above. It’s one thing to say that stars may decay and die into random gas clouds, but it is totally different to say that gas clouds form into stars.

    Even the father of Chaos theory admitted that the “mechanisms” existing in the non-living world allow for only very rudimentary levels of order to arise spontaneously (by chance), but not the kind or level of order we find in the structures of DNA, RNA, and proteins. Yes, individual amino acids have been shown to come into existence by chance but not protein molecules which require that the various amino acids be in a precise sequence just like the letters found in a sentence.

    Some things don’t need experiment or scientific proof. In law there is a dictum called prima facie evidence. It means “evidence that speaks for itself.”

    An example of a true prima facie would be if you discovered an elaborate sand castle on the beach. You don’t have to experiment to know that it came by design and not by the chance forces of wind and water.

    If you discovered a romantic letter or message written in the sand, you don’t have to experiment to know that it was by design and not because a stick randomly carried by wind put it there. You naturally assume that an intelligent and rational being was responsible.

    It’s interesting that Carl Sagan would have acknowledged sequential radio signals in space as evidence of intelligent life sending them, but he wouldn’t acknowledge the sequential structure of molecules in DNA (the genetic code) as evidence of an intelligent Cause. Read my popular Internet article, HOW DID MY DNA MAKE ME.

    I encourage all to read my popular Internet articles:

    NATURAL LIMITS TO EVOLUTION
    HOW FORENSIC SCIENCE REFUTES ATHEISM

    Visit my latest Internet site: THE SCIENCE SUPPORTING CREATION (This site answers many arguments, both old and new, that have been used by evolutionists to support their theory)

    Author of popular Internet article, TRADITIONAL DOCTRINE OF HELL EVOLVED FROM GREEK ROOTS

    *I have given successful lectures (with question and answer period afterwards) defending creation before evolutionist science faculty and students at various colleges and universities. I’ve been privileged to be recognized in the 24th edition of Marquis “Who’s Who in The East” for my writings on religion and science.

  • Tim Staffell

    Because you can’t envisage the natural development of complexity from simple beginnings, you invoke a sky fairy to explain first principles. Science is not simply observation, as you put it, it’s also deduction and calculation. Through evidence based extrapolation and confirmation Science asserts and demonstrates how simple matter has organised itself from prime first principles, and how life has evolved by responding to its surroundings. There is no need or evidence for a ‘designer’ None whatsoever.

  • Augustine yaw kumankumah Darkwah-Sarpong

    Of all that science has brought us the most fascinating is man’s ability to conquer the spheres of the universe by exploring the phantoms of the unknown,come to think of it what will the future be in our universal sciences,actually our understanding of reality is gradually been changed.
    Now the big question is who are we what is our world and what does the vast universe has for us.What truly is the meaning of reality and consciousness in relation to science as we have come to know it in our age.

  • Darkwah-Sarpong Augustine Kumankumah

    The epitome of required knowledge is the essence of all reality,now the mighty question is what is the belief of Hawkins and the other atheists scientists,do they believe in the originator of creation or not ,what they failing to recognise is that the originator of creation is neither a spirit or a being,so who is he ….. He is an unknown force emanating his presence for man to study his behavior in utopia.So in my research and understanding i’ve come to the realization that he is ( THE ULTIMATE DYNAMIC FORCE OPERATING WITHIN THE LEVEL OF HIS CREATION) So in my estimation all power ,knowledge,wisdom and insight rest upon that force,so until man respects and acknowledge that force all our efforts to exhumed knowledge of who we are and deciphering our very existence with and through sciences alone will be fruitless so it’s about time for the scientists to acknowledge him to assist them to have true knowledge of who we are.

  • Wescott

    The first of the gas-giant orbiter’s back-to-back flybys will provide a close encounter with the massive moon after over 20 years. On Monday, June 7, at 1:35 p.m. EDT (10:35 a.m. PDT), NASA’s Juno spacecraft will come within 645 miles (1,038 kilometers) of the surface of Jupiter’s largest moon, Ganymede.

    https://www.navyarmyccu.ltd/