For the needs of the ESA JUICE (Jupiter Icy Moon Explorer) mission, several IRAP researchers (Université Paul Sabatier of Toulouse & CNRS) have just realized a campaign of unpublished tests at the ONERA (Office National d’Etudes et de Recherches Aérospatiales, Toulouse). These tests were designed to measure the effectiveness of Langmuir probes for the first time covered in gold, diamond or graphene. These rare and expensive materials have interesting properties. But are they as effective as those traditionally used to determine the characteristics of a plasma?
The JUICE (Jupiter Icy Moon Explorer) mission was selected in 2012 as a Class L mission of the ESA Cosmic Vision program. Eight years after its launch scheduled for 2022, it will start its detailed study of the Jupiter system, a true miniature solar system. Its analyzes will more particularly focus on the Jovian magnetosphere and the three icy moons Ganymede, Callisto and Europe.
The objective of this mission is to answer the following questions of the ESA Cosmic Vision program : What are the conditions for planet formation and the emergence of life? How does the Solar System work?
To this end, various instruments will equip the spacecraft. Amon those chosen to contribute to the JUICE mission, there is the RPWI experience (Radio & Plasma Wave Investigation) (1), which will study the thermal plasma and the electric and magnetic fields generated by radio, plasma waves and the impacts of micrometeorites. The main objectives of RPWI will, firstly be the study of the interactions between Jupiter and its moons (in order to better characterize the oceans located under the surface), secondly to understand the magnetospheric dynamics, the acceleration of particles and the sources of radio wave emissions.
RPWI will notably be equipped with four Langmuir probes (2) designed to characterize the cold plasma regions (< 100 eV) of the Jovian system. These probes will lead to study the origin, the structure, the dynamics and the sources / sinks of the ionospheres of Ganymede and Callisto. As a result, the complete description of the plasma issued from the ionization of the exosphères of the icy moons of Jupiter or present in the rotating magnetosphere: density, temperature, plasma drift velocity and mean ion mass. The sensors will also provide key answers regarding the atmospheric erosion phenomenon (ionospheric exhaust) of Ganymede.
Within the framework of past or current space missions (Rosetta, MAVEN, Cassini, …), the surface of the Langmuir probes has often been coated with titanium nitride or titanium aluminum nitride. Experiments conducted within the JONAS facility of the ONERA at Toulouse were designed to test the effectiveness of other materials: gold, diamond and graphene – “miracle” material discovered in the 2000s. As an example, diamond has interesting properties: hardness, resistance to high temperatures. Enriched with nitrogen or boron, it also offers a high electrical conductivity (3), comparable to that of gold. The reliability and durability of onboard instruments constituting one of the key success of a space mission, the Langmuir probes will probably be for the first time covered with diamond.
(1) IRAP is involved in the JUICE mission through two different consortia, the PEP consortium (Particle Environment Package) and the RPWI consortium (Radio and Plasma Waves Instrument).
(2) The Langmuir probes are small metallic conductive balls mounted at the end of masts, to which a variable electric potential is applied to attract either the ions (negative potential) either the electrons (positive potential) of the environment. The curve of the current measured at the surface of these probes as a function of the applied electric potential allows to determine, by comparison with theoretical equations, the parameters of the surrounding plasma. The probe surface composition is therefore essential to obtain a signal of the highest quality.
(3) The JUICE probe will be equipped with four Langmuir probes – spheres of 10 cm diameter attached to the end of masts of 3 meters long. Their combination will lead to measure the electric field emitted by the ocean located below the surface of Ganymede, to characterize its electrical conductivity, and thus to constrain its salinity.
- Center for nanoscale materials (CNM) at Argonne National Laboratory (ANL), Etats-Unis
- Department of chemistry, inorganic chemistry, Uppsala University, Suède
- Department of engineering sciences, division of electricity, Uppsala University, Suède
- Department of engineering sciences, solid state electronics, Uppsala University, Suède
- Swedish institute of space physics, Uppsala, Suède
- Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France
- Office National d’Etudes et de Recherches Aérospatiales (ONERA), Toulouse, France
IRAP staff involved
- P. Garnier, N. André, O. Chassela, J. Rouzaud, E. Lecomte
- Philippe Garnier, firstname.lastname@example.org