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19 August 2013

BepiColombo is Europe’s first mission to Mercury, the innermost planet of the Solar System. It consists of two orbiters, one for planetary investigation and the other for magnetospheric studies. They will reach Mercury in 2023 after a 6,5-year journey towards the inner Solar System in order to make the most extensive and detailed study of the planet ever performed.

The 'Mercury Planetary Orbiter' (MPO), under ESA’s responsibility, will study the surface and the internal composition of the planet at different wavelengths and with different techniques. The Mercury Magnetospheric Orbiter (MMO), under the responsibility of the Japan Aerospace Exploration Agency (ISAS/JAXA), will study the planet’s magnetosphere. This is the region of space around Mercury that is dominated by its magnetic field.

Only two spacecraft have visited Mercury so far. NASA's Mariner 10 provided the first close-up images of the planet when it flew past three times in 1974-75. More than 30 years later, on 14 January 2008, NASA’s MESSENGER swung by Mercury. In the course of its journey to eventually settle in orbit around the planet in 2011, MESSENGER made two other flybys, on 6/10/08 and 29/09/09. The spacecraft provided new close-up images and scientific data of the planet.

When BepiColombo reaches its destination in 2023, it will be only the second spacecraft to orbit Mercury in the history of planetary exploration.

The difficulty of reaching, surviving and operating in the harsh environment of a planet so close to Sun makes BepiColombo one of the most challenging long-term planetary projects undertaken by ESA so far.

BepiColombo is named after Giuseppe (Bepi) Colombo (1920-84), a scientist who studied Mercury's orbital motion in detail and greatly contributed to the study of orbits and interplanetary travel.
BepiColombo will study and understand the composition, geophysics, atmosphere, magnetosphere and history of Mercury, the least-explored planet in the inner Solar System. In particular, the mission objectives are to:

  • understand why Mercury's density is markedly higher than that of all other terrestrial planets, the Moon included;
  • understand if the core of Mercury is liquid or solid, and if the planet is still tectonically active;
  • understand why such a small planet possesses an intrinsic magnetic field, while Venus, Mars and the Moon do not;
  • investigate whether Mercury's magnetised environment is characterised by features reminiscent of the aurorae, radiation belts and magnetospheric substorms observed at Earth;
  • understand why spectroscopic observations do not reveal the presence of any iron, while this element is supposedly the major constituent of the planet;
  • investigate whether the permanently shadowed craters of the polar regions contain sulphur or water ice;
  • observe the yet unseen hemisphere of Mercury;
  • study the production mechanisms of the exosphere and to understand the interaction between the planetary magnetic field and the solar wind in the absence of an ionosphere;
  • obtain new clues about the composition of the primordial solar nebula and about the formation of the Solar System;
  • test general relativity with improved accuracy, taking advantage of the proximity of the Sun and considering that the advance of Mercury's perihelion was explained in terms of relativistic space-time curvature.

ESA’s foreseen investment in BepiColombo, one the cornerstone missions of its scientific programme, is about 970 million Euros, covering the development of the spacecraft, the launch and the operations. The cost of the MPO instruments, funded by European institutes, is more than 200 million Euros.

Launch and journey

BepiColombo is currently scheduled for launch in 2016 from ESA’s Kourou station in French Guiana, on board an Ariane 5 rocket provided through Arianespace.

During the voyage to Mercury, which will last about 6,5 years, the two orbiters and a transfer module will form one single composite spacecraft. The launcher will place the mission straight into orbit around the Sun. Once on its cruise trajectory, the composite spacecraft will be accelerated by a combination of solar-electrical propulsion (SEP) and seven gravity-assistance manoeuvres (one at Earth, two at Venus, and four at Mercury itself) ) – a technique already tested at the Earth and the Moon on ESA’s SMART-1 mission to the Moon. Upon arrival at Mercury, the transfer module with the electrical propulsion system will be jettisoned. At this point the composite spacecraft will use conventional rocket engines and the technique called 'weak stability boundary capture’ to enter a polar orbit around the planet. When the MMO orbit is reached, the MPO will separate and lower its altitude by means of chemical propulsion to its own operational orbit.


The MPO and MMO final orbits will both travel over Mercury’s poles. The MPO orbit will range between 400 km and 1500 km above the surface of the planet, while the MMO orbit will range between 400 km and 12 000 km in altitude.
Planned mission lifetime
The BepiColombo scientific mission at Mercury is planned to last at least one Earth year. In principle the mission can be extended by an additional Earth year.
Design: Operating a spacecraft in the harsh environment of Mercury presents an enormous technological challenge. The direct solar radiation hitting the spacecraft is about ten times more intense than in Earth's proximity. Furthermore Mercury's surface, whose temperature can reach up to 470 °C, not only reflects solar radiation but also emits thermal infrared radiation. Therefore, the probe will have to withstand extreme thermal conditions.

Dimensions: The body of BepiColombo’s MPO will measure 2.4 x 2.2 x 1.7 m (excluding solar wings), while the radiator on one side of the spacecraft measures 3.7 m. With the solar wings extended, it measures about 7.5 m across. BepiColombo’s MMO will measure 1.9 x 1.1 m.

Mass: The MPO spacecraft will weigh 1140 kg, including 80 kg of instruments. The MMO spacecraft will weigh about 288 kg, including 45 kg of scientific instruments.

Industrial involvement: Astrium (Germany) is the prime contractor for the design and procurement of the 'cruise-composite' spacecraft, including the ESA’s MPO, the Mercury Transfer Module, the MMO’s sunshield and the interface between the MPO and the MMO. Furthermore it provides the design and development of the data management and attitude and orbit control subsystems, and the integration of the engineering model. Thales Alenia Space Italy will be the co-prime contractor for the development of the MPO’s electrical power, thermal control and communications systems and for the integration and test activities. In the UK, Astrium is co-prime contractor for the electrical and chemical propulsion systems, for the structure of all modules and for the thermal control of the Mercury Transfer Module. Astrium in France will develop the onboard software. The MMO and its scientific payload are designed and developed by JAXA. They are responsible for procuring the spacecraft from an industrial team led by NEC.
What’s on board?
Mercury Planetary Orbiter (ESA)
MPO will carry a highly sophisticated suite of eleven scientific instruments, ten of which will be provided by Principal Investigators through national funding by ESA Member States and one from Russia:

BepiColombo Laser Altimeter (BELA)
BELA will characterise the topography and surface morphology of Mercury. It will also provide a digital terrain model that, compared with the data from the MORE instrument, will give information about the internal structure, the geology, the tectonics and the age of the planet’s surface.
Co-Principal Investigators: N. Thomas, University of Bern, Switzerland, and T. Spohn, DLR, Germany.

Italian Spring Accelerometer (ISA)
The objectives of the ISA accelerometer are strongly connected with those of the MORE experiment. Together the experiments can give information on Mercury’s interior structure as well as test Einstein’s theory of the General Relativity.
Principal Investigator: V. Iafolla, CNR-IFSI, Italy.

Mercury Magnetometer (MERMAG)
The MPO’s MERMAG will provide measurements that will lead to the detailed description of Mercury’s planetary magnetic field and its source, to better understand the origin, evolution and current state of the planetary interior, as well as the interaction between Mercury’s magnetosphere with the planet itself and with the solar wind.
Principal Investigator: K.H. Glassmeier, Technical University of Braunschweig, Germany.

Mercury Thermal Infrared Spectrometer (MERTIS)
Providing high spectral resolution, MERTIS will return detailed information about the mineralogical composition of Mercury’s surface layer. This is crucial for selecting a valid model for the origin and evolution of the planet.
Principal Investigator: H. Hiesinger, University of Münster, Germany.

Mercury Gamma ray and Neutron Spectrometer (MGNS)
MGNS will determine the elemental compositions of the surface and subsurface of Mercury, and will identify the regional distribution of volatile depositions on the polar areas which are permanently shadowed from the Sun.
Principal Investigator: I. Mitrofanov, Institute for Space Research, Russia.

Mercury Imaging X-ray Spectrometer (MIXS)
MIXS will use X-ray fluorescence analysis to produce a global map of Mercury’s surface atomic composition at high spatial resolution. This technique has been also used by the D-CIXS instrument on ESA’s SMART-1 mission to the Moon.
Principal Investigator: G. Fraser, University of Leicester, UK.

Mercury Orbiter Radio science Experiment (MORE)
MORE will help to determine the gravity field of Mercury as well as the size and physical state of its core. It will provide crucial experimental constraints to models of the planet’s internal structure and will test theories of gravity with unprecedented accuracy. Its data will be used in conjunction with those from BELA and ISA to achieve these goals.
Principal Investigator: L. Iess, University of Rome ‘La Sapienza’, Italy.

Probing of Hermean Exosphere by Ultraviolet Spectroscopy (PHEBUS)
The PHEBUS spectrometer is devoted to the characterisation of Mercury’s exosphere composition and dynamics. It will also search for surface ice layers in permanently shadowed regions of high-latitude craters.
Principal Investigator: E. Chassefière, Université P&M Curie, France.

Search for Exosphere Refilling and Emitted Neutral Abundance (SERENA)
SERENA will study the gaseous interaction between Mercury’s surface, exosphere, magnetosphere and the solar wind.
Principal Investigator: S. Orsini, CNR-IFSI, Italy.

Spectrometers and Imagers for MPO BepiColombo Integrated Observatory System (SYMBIO-SYS)
SIMBIO-SYS will examine (also in stereo and colour) Mercury’s surface geology, volcanism, global tectonics, surface age and composition, and geophysics.
Principal Investigator: E. Flamini, ASI, Italy.

Solar Intensity X-ray Spectrometer (SIXS)
SIXS will perform continuous measurements of X-rays and particles of solar origin employing a very wide field of view.
Principal Investigator: J. Huovelin, Observatory University of Helsinki, Finland.

Mercury Magnetospheric Orbiter (JAXA)
MMO will carry five advanced scientific experiments that will also be provided by nationally funded Principal Investigators, one European and four from Japan. Significant European contributions are also being made to the Japanese instruments:

Mercury Magnetometer (MERMAG)
The MMO’s MERMAG will provide a detailed description of Mercury’s magnetosphere and of its interaction with the planetary magnetic field and the solar wind.
Principal Investigator: W. Baumjohann, Austrian Academy of Sciences, Austria.

Mercury Plasma Particle Experiment (MPPE)
MPPE will study low- and high-energetic particles in the magnetosphere.
Principal Investigator: Y. Saito, ISAS, JAXA, Japan.

Mercury Plasma Wave Instrument (PWI)
PWI will make a detailed analysis of the structure and dynamics of the magnetosphere.
Principal Investigator: Y. Kasaba, RISH, University of Kyoto, Japan.

Mercury Sodium Atmospheric Spectral Imager (MSASI)
MSASI will measure the abundance, distribution and dynamics of sodium in Mercury’s exosphere.
Principal Investigator: I. Yoshikawa, University of Tokyo, Japan.

Mercury Dust Monitor (MDM)
MDM will study the distribution of interplanetary dust in the orbit of Mercury.
Principal Investigator: K. Nogami, Dokkyo Medical University, Japan.
Ground control: ESA is responsible for the overall mission design, and for the operation of the composite spacecraft up to the insertion of the MPO and MMO into their orbits. During the cruise, the European Space Operations Centre (ESOC) in Darmstadt, Germany, will coordinate the operation of the full composite spacecraft by using the Cebreros 35 m antenna in Spain. The ISAS/JAXA Sagamihara Space Operation Centre, using the Usuda 64 m antenna (Japan), will take over the operation of the MMO once it is in orbit around Mercury, while ESOC will remain in charge of the MPO spacecraft.

Science operations: ESA is responsible for the mission and scientific operation of the MPO. The BepiColombo Science Operation Centre will be at the European Space Astronomy Centre (ESAC) in Villafranca, near Madrid, Spain. It will define and coordinate the scientific observations, and assist the teams in operating their instruments.

ESA Project Manager: Jan van Casteren
ESA Project Scientist: Johannes Benkhoff
ESA Spacecraft Operations Manager: Elsa Montagnon

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