David Rothery, Dept of Earth & Environmental Sciences

D.A.Rothery@open.ac.uk

X-Ray detection techniques and the BepiColombo-MIXS instrument

SolarCoronalPrimaryX-ray Flux

X-ray fluorescent and backscattered flux

Direction of MPO motion

Planetary X-ray Remote Sensing : BepiColombo MIXS (2013)

Fluorescent X-rays reveal:

Elemental composition to a depth of a few mfor low atomic number elements (eg Mg) and for L-shell emissionlines of heavier elements

For heavier elements, K-shell emission (higher energy) increasesthe sampling depth to tens of m

X-ray spectroscopy is complementary to:•gamma-ray and neutron spectroscopy (MGNS) low spatial resolutionmeasurements of a few elements to depths of 10 cm•Optical and IR spectroscopy (Simbio-Sys, MERTIS) sensitive tomineralogy (cation-oxygen bonds) to depths of tens of m

MIXS – Mercury Imaging X-ray SpectrometerPI George Fraser, University of Leicester

Two devices: MIXS-C (Collimator) MIXS-T (Telescope)

MIXS-C 10.4 degree FOV, optimised to provide the largest X-ray throughput at all energies for all solar states. Pixel size 70 km at periherm, 270 km at apoherm.

MIXS-T 1.1 degree FOV, angular resolution <9 arcmin.Spatial resolution < 1 km at periherm, 4 km at apohermBut achievable only during solar flares.

FOVs/pixels will be binned when signal is low. Effective spatial resolutionwill vary according to solar activity and will differ between elements.

Microchannel plate (MCP) optics, differently configured forMIXS-C and MIXS-T

MIXS-C

MIXS-T(Wolter type I optic)

Identical focal plane assemblies for MIXS-C and MIXS-T.64 x 64 array of Macropixel DEPFET detectors,measuring X-rays 0.5-7.5 keV

Energy resolution (will degrade because of radiation damage):100 eV at 1 keV at start of orbital tour<200 eV after one year at Mercury

MIXS-C at apoherm, 209s dwell-time

100 km

Best feasible MIXS-T resolutionSimulated mapping of Fe abundance

Assume brightness is proportional to albedo Assume albedo at 750 nm is proportional to FeO concentrationAssume FeO content is proportional to Fe concentrationAssume Si concentration is ~homogenous

Assume brightness is proportional to albedo Assume albedo at 750 nm is proportional to FeO concentrationAssume FeO content is proportional to Fe concentration

Assume Si concentration is ~homogenous

It is vital to know the intensity of the solar X-ray illumination, henceclose collaboration with SIXS (Solar Intensity X-ray Spectrometer)

Calibration issues

Roughness, grain size, packing density, incidence angle, emission angle?Experimental results under review (Näränen et al.)

Dynamic processes in Mercury’s magnetosphere such as:Dayside magnetic reconnection phenomena (or Flux Transfer Events, FTEs)ULF wave activityExtremely rapid substorm activity (few tens of seconds). (MIXS-T spatialresolution could be useful here)

Any of these could produce X-rays at the surface (or even in the exosphere)by means of precipitation and/or acceleration of electrons and/or ionsin large scale current systems associated with solar wind-magnetosphere-exosphere-surface coupling

Lots of scope for collaboration with HEWG members

Optics (focus tests)

MIXS T res could be needed for substorm, structure

Add telescope tubes after slide 4Cfrp carbon fibre reinforced polymer