A survey of the total organic and inorganic carbon (TIC/TOC) inventory is the highest level assessment of both biological history and habitability of a site. Moreover, it is a measurement of interest not only on Mars, but on any planetary body. By addressing TOC, we perform a high-level assessment of habitability and biological potential that does not depend on any specific molecular model. The ratio of organic to inorganic carbon is a model independent indicator of the extent to which chemical energy is available to biological entities. The ¹³C/¹²C ratio is a similarly generic indicator of biotic vs. abiotic material. ¹³C is depleted in biological systems, enhanced in carbonates. From a paleontological point of view, this measurement helps us understand the evolution of Martian organics. Do organics graphitize as on Earth, oxidize to CO₂, or do they form stable, possibly detectable intermediates?

Purely from an analytical stand-point, TIC/TOC is best measured by oxidizing the organics either chemically or electrochemically. In the chemical approach, inorganic carbon is converted to CO2 by an acid solution, while organic carbon is converted in an oxidizing solution. In the electrochemical technique the organic carbon is oxidized at a boron-doped diamond electrode. Assuming future Mars lamders will offer sample collection and grinding, the challenges to be addressed are the oxidation mechanism itself and the CO₂ detection against the background of a CO₂-rich atmosphere.

We are currently working to develop a Total Inorganic Carbon / Total Organic Carbon (TIC/TOC) analyzer capable of:

(1) determining quantitatively the relative proportions of total inorganic carbon (TIC) and total organic carbon (TOC) in planetary surface and near-surface samples.

(2) determining stable carbon isotope ratios for the TIC/TOC fractions.

The TIC-TOC Analyzer will be comprised of a wet chemical reaction chamber linked via a gas line and appropriate valving to a mass spectrometer for CO2 gas sensing. The envisioned flight instrument will heavily leverage existing flight hardware, integrating the MSP'01 MECA Wet Chemistry Experiment sample handling units, the Mars Polar Lander TEGA tunable diode laser spectrometer, and the MSP '01 MIP CO2 gas handling system.

A 99% pump/purge of CO2 gas in the head space prior to measurement will allow detection of TIC/TOC in the ppb range, assuming a detector with 0.1% sensitivity. Since the detector technology is mature, a commercial mass spectrometer will be used during the first stages of this study.