O2- ions and the Mars labeled release response.

Yen et al. (1) propose that O 2 – ions puta-tively formed in the soil of Mars, not microorganisms , represent " the most straightforward explanation " of my 1976 Viking labeled release (LR) life detection results. Data from radioactive organic nutrients added to martian soil (2), however, challenge that conclusion. In the data reported by Yen et al. [figure 3 of (1)], O 2 – radicals lose only 10% of their activity after one hour at 100 o C, and still retain 30% activity after an additional hour at 200 o C. These results differ sharply from the LR Mars control data. After martian soil samples had responded positively, duplicates of those samples, in accordance with the protocol of the Viking Biology Team, were heated before testing to distinguish between biological and chemical activity. Heating at 160 o C for three hours completely inactivated the sample, signifying biology. An added control run strengthened the case: heating at only 51 o C produced 95% inactivation. Yen et al. mention the inconsistency of their results with these data only in note 20 of (1). There, they cite a book by Horowitz (3) that sought to reconcile the heat sensitivity shown by the martian soil in the LR experiment with the soil's heat resistance, as shown in the Viking gas exchange (GEx) experiment (4). Horowitz conjectured that, when the LR soil was heated in its sealed test chamber, water vapor evolved to inactivate the (putative) chemical oxidant. On the other hand, he proposed that water vapor from soil heated in the GEx test chamber, purged to the atmosphere, did not destroy the oxidant. However, data (2) not mentioned by Yen et al. are more important. Soils at Viking 1 and 2, samples from each having produced positive LR reactions, were held in their distribution boxes for 141 martian days at 10 to 26 o C and for 84 martian days at approximately 7 o C, respectively. The box shields the soil from the sun, but is open to the martian atmosphere. Any water vapor evolving from the soil is thus free to escape. After storage, the soils were again tested. Their responses were essentially nil. In-activation at such low temperatures would seem to render the model relying on activity of O 2 – ions inapplicable to the Mars LR results. Over the quarter of a century since Viking, there have been more …