The drill and Ma_MISS prototypes during a series of drilling and sampling tests. Credit: SELEX Galileo

Located inside the ExoMars Rover's drill, Ma_MISS, the Mars Multispectral Imager for Subsurface Studies, will be the instrument in closest contact with the Martian subsurface. Ma_MISS will image the walls of the borehole created by the drill to study Martian mineralogy and rock formation. This will provide valuable information for the study of subsurface soil and rock layers (i.e., stratigraphy), the distribution and state of water-related minerals, and will help to characterise the geophysical Martian environment.

As the Rover drills into the upper surface of Mars, Ma_MISS will illuminate the hole's cylindrical wall through a transparent window situated in the drill tool. It will capture the reflected light, analyse its spectrum, and transfer the data on the hole stratigraphy to the Rover computer for further analysis and relay to Earth.

Ma_MISS exploits the movement of the drill to acquire data from all around the borehole. The rotation of the instrument as it descends will allow images to be built up in both horizontal (ring image) and vertical sequences (column image).

Ma_MISS's main science objective is to study the Martian subsurface. This is key to understanding the chemical and physical processes that led to the formation and evolution of the site being investigated.

The Martian surface is highly influenced by external processes such as weathering, erosion, sedimentation and impact, all of which alter its original properties. The investigation of subsurface layers is the only approach that permits measurements on samples close to their original composition. The analysis of unexposed material by Ma_MISS, together with data obtained from the spectrometers located inside the Rover (Raman, MicrOmega, MOMA), will be crucial for the interpretation of the original conditions of rock formation on Mars.

In-situ analysis of the Martian subsurface provides information that can be used in the following investigations:

• Assessing the habitability of the drilling site and searching for possible indicators of life.
• Determining the presence of ice or water at the drilling site.
• Documenting the mineral distribution and composition, and identifying the nature of local geology and chemistry.
• Studying the Martian surface layers in terms of hazards and resources relevant to the potential for survival of humans on the surface.

The sapphire window on the drill permits observation of the Martian soil, while the Ma_MISS optical head is protected from scratches and dust. Credit: SELEX Galileo

The Ma_MISS instrument includes:

• the optical head, which illuminates the borehole with a spot of approximately 1 mm diameter and then collects the reflected light coming from a 0.1 mm diameter area;
• the illumination system, located 0.2 mm from the window;
• the optical fibre, which transmits the light from the illumination system to the optical head and collects the reflected light to convey it to the spectrometer;
• the spectrometer, which acquires the collected visible and infrared light (0.4 µm - 2.2 µm) and measures its spectrum with a high precision (20 nm spectral resolution);
• the transparent sapphire window, which is placed on the wall of the drill to enable the observation of the soil, preventing the contamination by dust of the internal optical and mechanical elements and the risk of damage (scratches) to its surface; sapphire is almost as hard as diamond.

Part of the Ma_MISS electronics is located in a dedicated unit mounted outside the drill box. The transmission of power and data is possible through electrical and optical joints between the drill tool and the Ma_MISS unit. The Ma_MISS instrument elements are exceptionally miniaturised to comply with the limited space available inside the drill.

Instrument update

The drill prototype with the Ma_MISS sapphire window and optical head during a series of drilling and sampling tests. Credit: SELEX Galileo

The first drill tool prototype in which the Ma_MISS optical parts (the lamp, optical head, optical fibres and connectors, and sapphire window) were integrated was developed in October 2009. An instrument prototype has been successfully tested for design validation in laboratory tests. A functional verification of some of its elements after integration in the drill has been performed in 2010.

Tests of the Ma_MISS breadboard with reference material (tuff, red brick) have been carried out to evaluate and characterise the performance of the system. The tests have demonstrated that the instrument is capable of acquiring accurate response signals, reflected from representative minerals, such as olivine and gypsum.

Further tests of the drill tool prototype and the integrated Ma_MISS engineering model with analogue Martian samples (e.g sandstone, basaltic lava, geyserite, gypsum) are planned to validate the drill system performance.