14 DEC 2018

The mission, launched with an Ariane 5 rocket, will carry sixteen scientific instruments, which include several that have been designed by three Sorbonne University laboratories: the LESIA 1 (Laboratory of Spatial Studies and Instrumentation in Astrophysics), the LPP2 (Plasma Physics Laboratory) and LATMOS3 (the Atmospheres, Environments, Spatial Observations Laboratory).

The BepiColombo space mission was launched on 20 October for Mercury ©ESA

An unknown planet, essential to understanding of the solar system

Mercury is the closest planet to the Sun. This proximity combined with the absence of atmospheric protection means the planet experiences extreme temperature variations (from -180 ° C to + 430 ° C), as well as a level of solar radiation ten times higher than on Earth. This hostile environment, thermal constraints and the complex orbiting around Mercury make it difficult to send space probes and measuring instruments to this region.

Long neglected by space exploration, Mercury is still poorly known to scientists. Only two American missiles, the Mariner 10 spacecraft launched in 1973 and the 2004 NASA Messenger probe, have closely observed the planet. After the overflights of Mariner 10, the scientists were able to discover, thanks to the probe Messenger, the presence of ice at the bottom of the polar craters of Mercury. The probe also revealed a very intense volcanic activity and the existence of an asymmetrical magnetic field that is three times more intense in the northern hemisphere than in the southern hemisphere. Hollows were also observed which contained small blue deposits, signs of very recent activity on Mercury.

As the only rocky planet besides Earth to have a magnetic field, Mercury has the highest iron content in the solar system. Because of its unique position and makeup, it is a key element to understanding the formation of the solar system.

The scientific objectives of the BepiColombo mission

To better understand this planet, the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) have joined forces to launch the BepiColombo project. Estblished in 2003 with the collaboration of 14 European countries and Japan, this mission has several objectives, among which are:

  • Improve the knowledge of the planet (photographing the entire surface of Mercury in high resolution, studying its topography, the age of its surface, its chemical and mineralogical composition and its mass and internal structure)
  • Find the origin of Mercury’s magnetic field
  • Study gases, molecules and atoms
  • Analyze the magnetosphere4
  • Test general relativity and check the properties of gravitational physics

To fulfill these objectives, two probes are at the heart of the BepiColombo mission: one European, the Mercury Planetary Orbiter (MPO) and the other Japanese, the Mercury Magnetospheric Orbiter (MMO), renamed MIO by JAXA, according to Japanese tradition.

While the MMO probe will characterize the ionized environment of Mercury through magnetometers and multiple electric field and charged particle detectors, the MPO probe will investigate Mercury’s surface and very thin atmosphere.

By analyzing the composition of the surface of the planet, scientists hope to gain insight into the formation of Mercury and the solar system. A laser altimeter will map the relief of the planet and study the impacts of meteorites. Volcanic activity or the contraction of the planet due to its cooling have left marks that can provide valuable information on its history. Scientists also want to collect data on the nucleus by studying its gravitational field to better understand what makes it so similar and so different from the Earth's core.

The contribution of the Sorbonne University laboratories

Of the eight French laboratories that participated in designing some of the mission's scientific equipment, three Sorbonne University laboratories—LATMOS, LESIA and LPP—actively contributed to the development of several instruments.

The LPP contributes to the design and production of two instruments aboard the MMO probe:

  • The MSA (Mass Spectrum Analyzer), dedicated to measuring the composition of the plasma, will study the solar wind, the material ejected from the surface of Mercury, the transport and the acceleration of the ions in the magnetosphere, and the interaction of the magnetospheric plasma with the surface and the exosphere5 of the planet.
  • The DB-SC magnetometer (Double Band - Search Coil) will measure the fluctuations of the electromagnetic waves of the magnetic field.
Mass Spectrum Analyzer ©LPP

The LESIA has developed two instruments:

  • The Visual and Infrared Hyper-spectral Imager (VIHI) will provide unprecedented spatial and spectral resolution in a complete mapping of surface minerals. This information will help scientists to understand the processes that contributed to Mercury’s formation.
  • The SORBET High Frequency Radio Wave receiver (in French: Spectroscopie des Ondes Radio et du Bruit Electrostatique Thermique) will measure the density and temperature of the plasma in the Mercury environment. It will study the radio emissions of Mercury and the sun.

The LATMOS also contributed to this mission with two PHEBUS spectrometers, PICAM, housed on the MPO probe.

  • The PHEBUS Optical Spectrometer, which covers spectral ranges from extreme ultraviolet to distant ultraviolet, aims to characterize the Mercury exosphere and its relationship to the planet's surface.
  • The PICAM Ion Mass Spectrometer (Planetary Ion CAMera) will study the chain of processes by which neutrals are ejected from the regolith, then ionized and transported into the Mercury environment.

For more information

1 Co-management by Sorbonne University, CNRS, École Polytechnique, Paris-Sud University, Paris Observatory

2 Co-management by Sorbonne University, CNRS, Paris Observatory

3 Co-managed by Sorbonne University, CNRS, University Versailles Saint-Quentin

4 The magnetosphere is the area around a celestial body whose physical characteristics are governed by the magnetic field of the celestial body.

5 The exosphere is a neutral envelope (a very sparse atmosphere) of a celestial body.