July 4, 2016: The Juno probe has a rendezvous with Jupiter

The Juno Mission

Juno is a NASA space mission to study the planet Jupiter. The structure of this gas giant planet, its mode of formation but also the functioning of its magnetized environment, at the launch of the mission, are far from being clarified despite several space missions and astronomical observations made from Earth. The space probe, launched in 2011, must collect data on the inner layers of Jupiter, the composition of its atmosphere and the characteristics of its magnetosphere. These elements should make it possible to reconstruct the way Jupiter formed and to correct or refine the scenario for the formation of the planets of the Solar System in which Jupiter, because of its large mass, played a major role, and to specify the dynamics of its magnetosphere, archetypal of rapidly rotating magnetized systems.

The scientific phase of the mission will begin on July 4. Juno must carry out its observations from a very elliptical polar orbit over a period of 11 days that takes the probe at a very low altitude above the planet from pole to pole, largely avoiding the very intense radiation belt that could damage it. The mission must last at least one year, during which time Juno will make 37 flights over the planet.

Juno is carrying eight scientific instruments, including two spectrometers, a radiometer, a magnetometer and a set of instruments dedicated to the study of Jupiter’s poles. Juno is the first space probe to fly to an outer planet that uses solar panels instead of radioisotope thermoelectric generators. Juno is the second mission of the New Frontiers program, which includes missions to explore the Solar System with a medium budget. Its total cost is $1.1 billion.


Juno aims to reconstruct the history of Jupiter’s formation and evolution, and to clarify the functioning of its magnetosphere, known to generate the most powerful polar auroras in the Solar System. Given the role played by the giant planet in the formation of the Solar System, the elements obtained should make it possible to refine the theories in this field and to better understand the planetary systems discovered around other stars. Despite the data collected by astronomers and space probes that preceded Juno, at the time of the probe’s launch, Jupiter remains a poorly known planet. Juno is expected to make observations that will answer the following questions:

…its mode of formation;

  • the proportion of water and oxygen present;
  • its internal structure;
  • the way the different strata of the planet move relative to each other;
  • the presence of a solid core and its size;
  • how the magnetic field is generated;
  • the relationship between the movement of the atmospheric layers and the internal movement of the planet;
  • the mechanisms behind the aurora;
  • the characteristics of the polar zones.

The probe must seek information on several important topics:

  • The composition of the atmosphere
  • The structure of the atmosphere
  • The magnetic field
  • The magnetosphere at the poles
  • The field of gravity

Scientific equipment

Juno is carrying eight sets of instruments comprising a total of 29 sensors and the camera (JunoCam). These instruments include a microwave radiometer (MWR) to probe the deep layers of the planet’s atmosphere, a magnetometer (MAG) to measure the internal and external magnetic field, and a radio gravity experiment (GS, Gravity Science) to establish the internal structure of Jupiter. Finally, five instruments are more particularly dedicated to the study of the magnetosphere and the polar aurora: an infrared spectrometer (JIRAM), an ultraviolet spectrometer (UVS), a plasma and radio wave detector (WAVES), the energetic particle detector (JEDI) and a thermal particle detector (JADE). It is mainly to this experiment that the IRAP teams contributed, in particular for the three electron spectrometers (seen below).

Further Resources

The planet Jupiter

Jupiter is the largest of the planets in the Solar System with a mass that is two and a half times that of all the other planets and a diameter that is more than 11 times that of the Earth (about 138,000 km). It is one of the outer planets of the Solar System like Saturn, Uranus and Neptune and is also a giant gas planet. Jupiter is composed mainly of hydrogen and helium, like the Sun, with probably a rocky central core with a mass equivalent to ten times that of the Earth. The planet rotates on itself in just under 10 hours. Located 5.2 AU from the Sun, it completes its orbit around the Sun in 11.9 Earth years. Jupiter gives off more heat than it receives from the Sun: as the planet cools, it slowly contracts, which in turn generates localized heating in its core. This heat is transported by convection to the planet’s surface and is probably responsible for the complex and violent movements of Jupiter’s atmosphere. The atmosphere, 5,000 km thick, is made up of 3 layers: up to 100 km deep, clouds of ammonia ice, around 120 km deep, clouds of ammonium hydrogen sulphide and from 150 km deep, clouds of water and ice. At greater depths, hydrogen under enormous pressure is transformed into metallic hydrogen, which conducts electricity like a metal. The movements within this metallic liquid are probably at the origin of the planet’s intense magnetic field, (Jupiter’s magnetic moment is 20,000 times that of the Earth!) which traps electrons and ions creating a particularly powerful radiation belt. Jupiter’s magnetosphere, the area of space under the influence of this magnetic field, extends up to 3 million kilometres in the direction of the Sun and up to 1 billion kilometres in the opposite direction. If it were visible, it would be the apparent size of the full moon. Jupiter has 67 natural moons. The four main ones, Io, Europa, Ganymede and Callisto, are among the largest natural satellites in the Solar System and have remarkable characteristics: intense volcanic activity in the case of Io, and the supposed presence of oceans composed of liquid water below the surface in the case of Europa and Ganymede. Jupiter, because of its mass, played a very important role in the process of formation of the other planets of the Solar System and thus of the Earth, in particular by acting on their orbits and helping to gradually cleanse the Solar System of minor celestial bodies likely to strike them.

An ill-defined training scenario

The atmospheric probe launched by Galileo into Jupiter’s atmosphere has detected proportions of chemical elements that call into question the hypotheses on the formation of the planet and consequently the theories established on the origins and evolution of the Solar System.11 The atmospheric probe launched by Galileo into the atmosphere of Jupiter has detected proportions of chemical elements that call into question the hypotheses on the formation of the planet and consequently the theories established on the origins and evolution of the Solar System.11 The atmospheric probe has detected proportions of chemical elements that call into question the hypotheses on the formation of the planet and consequently the theories established on the origins and evolution of the Solar System.12 The atmospheric probe launched by Galileo into the atmosphere of Jupiter has detected proportions of chemical elements that call into question the hypotheses on the formation of the planet and consequently the theories established on the origins and evolution of the Solar System.13

  • Assumptions and questions in 2011 about the internal structure of Jupiter. Jupiter seems to be poor in water whereas according to the theories in force, water is considered as an indispensable medium for the incorporation of heavy elements during the formation of the planets of the outer Solar System of which Jupiter is a part. These elements are abundant on Jupiter. The answer that will be given to this question will have repercussions on the scenario of formation of planets with characteristics close to those of the Earth.
  • Two scenarios clash over the way Jupiter was formed: according to the first scenario, the planet was formed in two stages – accretion of materials located in its vicinity until it formed a solid core representing about ten Earth masses and then gravitational collapse of the mass of gas and dust surrounding the planet; the second scenario is based on the sole gravitational collapse of a cloud of dust and gas but requires the presence of an original nebula larger than the one retained in the scenarios of formation of the Solar System. Confirmation of the presence of a solid core at the heart of Jupiter and the determination of its composition could make it possible to make a decision.
Assumptions and questions in 2011 about the internal structure of Jupiter.

Previous missions

Beginning in 1973, several space probes carried out overflight maneuvers that placed them within observation range of Jupiter.

The exploration of Jupiter’s outer planets, including Jupiter, did not begin until 1973, while the inner planets had already been visited by several dozen space probes. Several spacecraft will fly over Jupiter later, but only Galileo will make an extended stay after orbiting the planet.

  • 1973: The first probe to approach Jupiter is Pioneer 10, which passes at a distance of 130,000 km from the planet on December 3, 1973 and discovers its radiation belt.
  • 1974: Pioneer 11 flies in turn over Jupiter (distance 34000km). In spite of their very simple instrumentation, both probes reveal the complexity of Jupiter’s atmosphere, provide images of very high quality as well as the first data on the planet’s magnetosphere.
  • 1979: The Voyager 1 and 2 probes, 349,000 km and 570,000 km respectively, equipped with much more scientific instrumentation, fly over the planet. They discover the faint rings around Jupiter, several new moons and volcanic activity on the surface of Io.
  • 1992: Ulysses studies the magnetosphere of Jupiter (distance 409 000km).
  • 1995: The Galileo probe orbits Jupiter for the first time. It reaches Jupiter in December and begins an 8-year exploration mission. In spite of a faulty satellite dish with a high gain that strongly affects the amount of data that can be transmitted, Galileo manages to transmit information about the entire Jovian system. At the beginning of its scientific mission Galileo releases a small atmospheric probe that penetrates Jupiter’s atmosphere and provides the elemental composition of the upper layers of Jupiter before being crushed by pressure. The data collected challenge some of the accepted theories about the process of planet formation in the Solar System, with the discovery of a very small proportion of water in the atmosphere. IRAP teams are still working on the scientific exploitation of this mission.
  • 2000: the Cassini probe (distance 10 000 000 km), on its way to Saturn, flies over Jupiter: it takes high-resolution images of the planet and, in coordination with the Galileo probe, studies its very large magnetosphere and its interactions with the solar wind. The intensity of the radiation belt is measured more accurately and turns out to be much higher than expected. This information is used to dimension the Juno probe’s shielding. IRAP is a direct contributor to two of the mission’s instruments and participates in the data analysis of all magnetospheric instruments.
  • February 28, 2007: the New Horizons probe is the last one to fly over Jupiter. The probe observes lightning at the poles, the creation of ammonia clouds and studies the circulation of charged particles in the magnetic tail of the planet.

Future missions

2022 mission JUICE : future mission of the European Space Agency, JUICE will be launched from the space port of Kourou for an 8-year voyage, an arrival programmed in 2030, for 3 years of detailed observations.

JUICE will continuously study Jupiter’s atmosphere and magnetosphere, as well as the interactions of its moons with the gas giant. It will visit Callisto, the object in the Solar System with the largest number of craters, and will conduct two overflights of Europa. JUICE will measure for the first time the thickness of Europa’s icy crust and identify suitable sites for future in situ exploration. The satellite will then orbit Ganymede in 2032 to study the moon’s ice surface and internal structure, as well as its subsurface ocean. Ganymede is the only moon in the Solar System to generate its own magnetic field and JUICE will observe in detail the unique magnetic and plasma interactions of this field with the Jovian magnetosphere.

JUICE will give us a better insight into how gas giants and the worlds that revolve around them are formed, and how they can harbour life. IRAP participates in the instrumental suites ‘waves’ and particles.

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