Perseverance’s Scanning Habitable Environments withRaman and Luminescence for Organics and Chemicals(SHERLOC) Investigation

The Scanning Habitable Environments with Raman and Luminescence for Organics
and Chemicals (SHERLOC) is a robotic arm-mounted instrument on NASA’s Perseverance
rover. SHERLOC has two primary boresights. The Spectroscopy boresight generates
spatially resolved chemical maps using fluorescence and Raman spectroscopy coupled to
microscopic images (10.1 μm/pixel). The second boresight is a Wide Angle Topographic
Sensor for Operations and eNgineering (WATSON); a copy of the Mars Science Laboratory
(MSL) Mars Hand Lens Imager (MAHLI) that obtains color images from microscopic
scales (∼13 μm/pixel) to infinity. SHERLOC Spectroscopy focuses a 40 μs pulsed deep UV
neon-copper laser (248.6 nm), to a ∼100 μm spot on a target at a working distance of ∼48
mm. Fluorescence emissions from organics, and Raman scattered photons from organics
and minerals, are spectrally resolved with a single diffractive grating spectrograph with a
spectral range of 250 to ∼370 nm. Because the fluorescence and Raman regions are naturally
separated with deep UV excitation (<250 nm), the Raman region ∼ 800 – 4000 cm−1
(250 to 273 nm) and the fluorescence region (274 to ∼370 nm) are acquired simultaneously
without time gating or additional mechanisms. SHERLOC science begins by using an Autofocus
Context Imager (ACI) to obtain target focus and acquire 10.1 μm/pixel greyscale
images. Chemical maps of organic and mineral signatures are acquired by the orchestration
of an internal scanning mirror that moves the focused laser spot across discrete points on
the target surface where spectra are captured on the spectrometer detector. ACI images and
chemical maps (< 100 μm/mapping pixel) will enable the first Mars in situ view of the spatial
distribution and interaction between organics, minerals, and chemicals important to the
assessment of potential biogenicity (containing CHNOPS). Single robotic arm placement
chemical maps can cover areas up to 7x7 mm in area and, with the < 10 min acquisition
time per map, larger mosaics are possible with arm movements. This microscopic view of
the organic geochemistry of a target at the Perseverance field site, when combined with
the other instruments, such as Mastcam-Z, PIXL, and SuperCam, will enable unprecedented
analysis of geological materials for both scientific research and determination of which samples
to collect and cache for Mars sample return.