Using small X-ray CT scanner for analysis of extraterrestrial samples. A. Tsapin, Jet Propulsion Laboratory, Cali-
fornia Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109. tsapin@jpl.nasa.gov
We propose to use a small light (2.5 kg with electronics and computer) a high resolution X-ray tomograph for non-destructive 3D imaging of internal
micro-architecture of opaque objects. The tomograph will register maps of density with 10 micron resolution inside of opaque samples (rocks,
ices, soil) with diameter up to 2.5 cm, and as long
as 10-15 cm. Such instrument will be extremely useful for analysis of internal structures of opaque material including cores. Also, it can provide insights on
endolithic (living inside rocks) organisms. On a mission to remote environments on Earth or to a distant
planetary surface, the field/flight versions of our system will identify samples worthy of further in situ
analysis by more time consuming or destructive
techniques, and select samples for return to Earth.
We will analyze 4 types of samples – rocks with
cryptoendolithic communities from dry deserts of
California and Antarctica; hematite concretions
(from Utah and California deserts) similar to ‘blueberries’ discovered by rovers on Mars; Precambrian fossilized microbes, and Archean, Proterozic,
and Cenozoic stromatolites. The tomograph provides image acquisition with spatial resolution of
10 micrometers and creates 3D density maps of
sample interior. The development of nondestructive survey tools to acquire 3D morphological
maps that can provide the evidence of extant life or
its fossil remnants hidden within opaque matrices
constitutes a core requirement for the astrobiological
exploration of Mars and Europa.
A fundamental goal of the NASA Astrobiology
program roadmap is "Determine whether there is (or
once was) life elsewhere in our solar system, particularly on Mars and Europa." To accomplish this goal
new methods such as the micro-CT must be developed that allow one to look inside enclosed environments, such as a rock, where life (or the residual signatures of life) can persist despite harsh exterior
conditions. Most notably on Earth, microbial communities living inside of rocks (known as endoliths)
appear to survive such extreme environments as the
cold, dry deserts of Antarctica. Dry Valleys, Antarctica currently serve as “Mars analog” test grounds for
developing geochemical instrumentation and techniques.
The X-ray tomograph will be able to produce 3D
images of the interior of opaque rock, soil and ice
samples, with the goals of identifying:
- which samples are worthy of further in situ
analyses by other more time consuming and destructive techniques;
- which samples are of high potential value for
return to Earth.
The typical scanning time for micro-CT is only a
few minutes for the entire volume.
The ability to "look inside rocks" and identify interior regions capable of supporting life either now
or in the distant past constitutes a core step in the
initial analytical exploration of the geobiochemical
history of a terrestrial planet. Combining rock structural information with knowledge of the elemental
composition of the samples provides a basis for classification and selection in terms of their importance
for Astrobiology. Astrobiological surveys of a planet
require instrumentation capable of recognizing signatures of extant and past life at a variety of scales.
Orbital imaging and spectroscopy give us spatial
resolutions at the meter to kilometer level. PanCam
wide angle and high resolution cameras provide information at centimeter and millimeter scales, respectively. Low magnification microscopes such as
the ExoMars CULPI provide resolutions at fractions
of a millimeter. UV-VIS-NIR epifluorescence microscopic imaging, confocal laser scanning microscopy,
and Raman imaging can provide resolutions in the
micrometer to fractions of a micrometer range. The
noninvasive X-ray tomography with a spatial resolution of 5- to 30- microns fills a much needed
scale between the low resolution survey imaging
systems and the high resolution microscopy tools.
This is particularly important when exploring endolithic communities or searching for fossil evidence of
past life. Microbial biology is almost always
"patchy". Microbial communities may thrive in one
small niche, but can be absent within a few millimeters and then reappear in profusion. The patches are
usually organized on a larger scale into layered deposits such as endolithic assemblages, finely laminated microbial mats, or stromatolites. Both the
patches and the organization of the community can
be identified at proposed spatial resolution. The relatively wide field of view (25 x 25 mm) provides a
much needed survey scale to optimize use of the
submicrometer scale tools. For example, original
density surveys will allow identifying sites likely to
contain either extant life forms or the carbonaceous
remains of organic past organic material.
Even though the resolution of proposed tomography is not enough to image a single microbial cell
(average diameter of microorganism is 1 micron), but
the instrument takes advantage of the fact that microorganisms tend to create communities, which can be
detected by our instrument.