MIXS - Mercury Imaging X-ray Spectrometer

The Mercury Imaging X-ray Spectrometer (MIXS) onboard ESA's mission BepiColombo to Mercury will measure X-rays emitted from the surface and the magnetosphere.

Fluorescent X-rays, due to solar X-ray absorption, reveal the elemental composition and abundances and this in turn is a tool for determining the geological history and ultimately the formation mechanisms for the planet. X-ray spectroscopy can be used along side complementary measurements at optical and infrared wavelengths which indicate chemical bonding and mineralogy.

The instrument consists of 2 instrument heads for high and low spatial resolution. The X-rays are collimated via a mirco-channel plate optics on to an energy dispersive solid state detector. BepiColombo was launched in October 2018 with an Ariane V rocket and will orbit Mercury from end of 2025 onwards.

Science objectives

The primary scientific aim of MIXS is to produce global elemental abundance maps of key-rock forming elements to an accuracy of 10-20%, such as Mg, Al, Si, Ca, Ti and Fe. In particular, MIXS allows researchers to determine the elemental abundance from regions of interest of Mercury's surface.

The main science objectives of MIXS are:

  • From what material did Mercury form, and how?
  • How and when did Mercury become internally differentiated?
  • Is there both primary and secondary crust on Mercury?
  • What is the history of crustal evolution on Mercury?
  • How does crustal composition vary (i) across the surface, (ii) with depth?
  • How are the surface and exosphere related?
  • How do the surface and magnetosphere interact?
  • Confirm that the auroral zone, where energetic particles interact with the surface, is an intense source of continuum and line X-ray

The Instrument

MIXS The Mercury Imaging X-ray Spectrometer (MIXS) is designed to perform X-ray fluorescence (XRF) analysis of the surface of Mercury. XRF is a well known technique used for remote sensing the atomic composition of airless, inner solar system bodies. XRF experiments require a source to illuminate the target - in the case of planetary XRF, the only source available is the Sun, which is a variable source and which varies in a non-constant way. In order to calibrate the MIXS instrument and obtain absolute abundances from its measurements, the solar input needs to be known. MIXS will obtain this reference information from its partner instrument, SIXS (Solar Intensity X-ray and particle Spectrometer). MIXS will detect K and L shell fluorescence line emission in the top few microns of the surface in the 0.5-7.5 keV energy range. This covers the emission energy of a number of important elements, including Mg, Al, Si, S, Ca, Ti and Fe.

MIXS consists of two channels - the MIXS-C, a collimator providing efficient flux collection over a broad range of energies with a wide field of view for planetary mapping and the MIXS-T, an imaging telescope with a narrow field for high resolution measurements of the surface. Both optical channels are read out by radiation hard, cooled (-40 °C) focal plane Macropixel Active Pixel Sensor DEPFET (DEpleted P-channel Field-Effect Transistor) arrays (resolution 100 eV at 1 keV).


Operation of the MIXS instrument will take place continuously on the day- and night-side of Mercury. Night side observations will be possible as there is a large flux contribution expected from auroral arcs at Mercury. The data will be processed and calibrated on the ground at the national institutes of the MIXS team.

The MIXS team

The MIXS team is headed by PI Emma Bunce, University of Leicester (UK). The German contribution to MIXS is financed by the Max Planck Society. The MPS is responsible for the scientific calibration of the detector units and the MPE contributes the flight-pixel-detectors.

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