The Atacama Desert is a very inhospitable environment for most forms of life due
to its lack of precipitation, high levels of UV radiation, and oxidant-rich soil.
In order to identify even the slightest trace of life, ZoŽ is equipped with specialized tools and sensors.
One way of detecting microscopic life is to take advantage of fluorescence.
Fluorescence occurs when a substance absorbs light of one wavelength and emits
light of a longer wavelength. At an atomic level, this phenomenon occurs when an
electron absorbs the energy from an incoming light photon and jumps to a higher
energy state, or orbital. Since this excited state is unstable, the electron will
eventually return to its natural state and in doing so release energy as heat and
light. The emitted light has a longer wavelength (meaning a lower frequency and
thus less energy) than the excitation light because some of the energy was released
as heat. A common example of non-biological fluorescence is white t-shirts that
appear to glow under black lights (which emit harmless UV-A light) because of
phosphors from laundry detergents.
Some organisms fluoresce naturally while others can be made to do so with
special chemical dyes. These dyes are carefully engineered to fluoresce once
attached to specific organic molecules. The excitation and emission wavelengths
of these dyes can be made to vary and thus be distinguishable from one another.
ZoŽ will be using four different dyes to identify proteins, lipids, carbohydrates,
The fluorescence imager is composed of a digital camera, a light intensifier, an
assortment of light filters, bright LEDs (Light Emitting Diodes), and a dye
application system. A cooled CCD camera allows for very low-noise images of samples
to be taken. Coupled to the camera, the intensifier simply amplifies weak light
sources and is intended to make daytime measurements possible, when the difference
in intensity between ambient light and sample flourescence is greatest. A filter
wheel in front of the intensifier allows for pictures to be taken at specific light
frequencies matching those that a sample might emit. The LEDs are chosen so that
their light wavelength can be absorbed by samples yet blocked by the filters.
Finally, the dye application system allows for samples to be sprayed with a fine
mist of fluorescence-inducing dyes.
ZoŽ will be equipped with a visual/near-infrared spectrometer tuned to detect
chlorophyll. Chlorophyll is the molecule in plants and bacteria that performs
photosynthesis, or the conversion of light energy into chemical energy that can be
used by biological systems.
A spectrometer works by analyzing the light reflected from a sample. It turns
out that the reflected light contains a great deal of information about the atoms
contained within a sample. Just like everyone has a unique fingerprint, each atom
has particular wavelengths of light that it reflects, called its emission spectrum,
and a complimentary set of wavelengths that it absorbs, called its absorption
spectrum. Thus, the emission spectrum for a molecule would be some combination of
the emission spectrum of its constituent atoms. By spreading the reflected light
out into a spectrum, much like a prism creates a rainbow, the spectrometer can
measure the intensities of light at different parts of the spectrum and thus
detect what atoms are present. ZoŽ's spectrometer will only look at visible and
near-infrared light, which constitutes only a small portion of the entire light
spectrum. In increasing frequency and energy, the forms of light include radio
waves, microwave, infrared, visible, ultraviolet, x-rays and gamma rays.
Since some organisms may not be living on the surface, ZoŽ will be equipped with
a simple plow-like device to flip over rocks and expose subsurface soil. Stored in
the underbelly, the plow will be lowered to the ground and held in place while the
robot drives forward, thus digging a small trench. The fluorescence imager and
spectrometer would then be used to examine the newly exposed surfaces.
|An example of what a processed fluorescence image could look like.|
|Hyperion tests out a prototype fluorescence imager at night.|
|Testing the plow design with Hyperion.|