Bepi Colombo

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.

The instrument consists of 2 heads, one for high and one for low spatial resolution. BepiColombo was launched in October 2018 with an Ariane V rocket and will orbit Mercury from end of 2025 onwards.

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. 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) DEPFET (DEpleted P-channel Field-Effect Transistor) Macropixel focal plane arrays (resolution 100 eV at 1 keV).

DEPFET Macropixel sensor was developed at MPG HLL and system development was a collaborative effort with Max Planck Institute for extraterrestrial Physics and Max Planck Institute for Solar System research.

DEPFET Macropixel characteristics :

  • Format
    • 1.92 x 1.92 cm 2
    • 64 x 64 pixels
    • 300 x 300 mm 2 pixel size
  • Time resolution
    • < 1 ms due to dynamics
  • Energy resolution
    • 200 eV FWHM @ 1 keV
    • QE > of 80 % @ 500 eV
  • Radiation hardness
    • ~ 20 krad ionisierend
    • equivalent to 1.11 x 10 11 1 MeV n/cm 2


MIXS DEPFET pixel layout

MIXS DEPFET pixel layout

Assembled MIXS DEPFET sensor

Assembled MIXS DEPFET sensor


Majewski, P.; et al.;”DEPFET macropixel detectors for MIXS: First electrical qualification measurements”; IEEE Transactions on Nuclear Science 57(4):2389 – 2396; Sep 2010 DOI: 10.1109/TNS.2010.2053557

Majewski, P.; et al.;”DEPFET Macropixel Detectors for MIXS: Integration and Qualification of the Flight Detectors”; IEEE Transactions on Nuclear Science 59(5):2479-2486, Oct 2010 DOI: 10.1109/TNS.2012.2211616

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