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, Zoë is equipped with specialized tools and sensors.

Fluorescence Imager

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. Zoë will be using four different dyes to identify proteins, lipids, carbohydrates, and DNA.

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.

Spectrometer

Zoë 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. Zoë'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.

Plow

Since some organisms may not be living on the surface, Zoë 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.