MapX: An In-situ X-ray µ-Mapper for Habitability and Biosignature Studies

   Introduction: The search for evidence of life or its processes on Mars takes on two major themes: 1), the identification of environments that have or once had the potential to harbor life (habitability); and 2), the detection of morphological or chemical features suggestive of extinct or extant life (biosignatures).  Compositional heterogeneity at the mm-to-100µm scale can reveal geological processes indicative of past or present habitability, and morphological and compositional heterogeneity on a similar length scale can provide evidence of life’s processes.  The Mapping X-ray Fluorescence Spectrometer (MapX) is an arm-based in-situ instrument designed to identify these features on planetary surfaces [1].

 Instrument Description: MapX is a full-field elemental imager capable of analyzing samples in situ without sample preparation. MapX has no moving parts, a 1-cm depth of field, and is designed to utilize ²⁴⁴Cm radioisotope sources, eliminating the need for a High Voltage Power Supply or X-ray tube.  Figure 1 shows a schematic of the instrument, which consists of X-ray / ϒ-ray / α-particle sources, a focusing optic, and a CCD. The focusing lens is an X-ray micro-pore optic (MPO) which focuses X-ray photons 1:1 onto the CCD. The MPO has a large depth of field (~1cm) allowing rough unprepared surfaces to be imaged with minimal loss of resolution. The CCD is read out fast enough (several frames per second) so that each pixel records either a single photon from the sample or background. The number of electron hole pairs generated in a single pixel is directly proportional to the energy of the X-ray photon, and after summing a large number of individual frames, an XRF spectrum is generated for each pixel of the CCD. Each individual 0.3 sec. frame is a complete image; however many frames are necessary to produce quantifiable XRF spectra. Longer collection times will allow for improved signal to noise, but in the event a collection is interrupted the partial data will still yield a complete image.  Downlinked data products include:  Elemental maps 11

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