1. John Wenz, “16 Times We Didn’t Find ET,” Discover, Vol. 39, October 2018,pp. 64-65
2. If considerable oxygen and anaerobic bacteria are present, water and carbon dioxide will be produced, instead of methane.
3. Valerio Poggiali, “Methane-Filled Canyons on Titan,” Nature, Vol. 536, 18 August 2016, p. 253.
4. H. B. Niemann, et al., “The Abundances of Constituents of Titan’s Atmosphere from the GCMS Instrument on the Huygens Probe,” Nature, Vol. 438, 8 December 2005, p. 779.
5. Vittorio Formisano et al., “Detection of Methane in the Atmosphere of Mars,” Science, Vol. 306, 3 December 2004, pp. 1758–1761.
u Sushil K. Atreya, “The Mystery of Methane on Mars and Titan,” Scientific American, Vol. 296, May 2007, pp. 42–51.
u See Endnotes 37–u on page 331.
6. “A little over 100 metric tons of methane would have to be produced [on Mars] each year to maintain a constant global average of 10 ppbv [parts per billion by volume].” Atreya, p. 46.
u About 45% of organic matter and 75% of methane is carbon by weight. Anaerobic bacteria convert about 76% of the available carbon to methane. Assume that eleven comets (or asteroids), weighing 1016 grams each, struck Mars and only one hundred thousandth of each impactor consisted of organic matter. That would allow 100 metric tons of methane to slowly escape into Mars’ atmosphere for each of 5,000 years. (1 metric ton = 106 grams.)
Other reasonable combinations of numbers produce similar results, so more carbon should still be trapped in Mars’ soil.
7. Microbial cells, such as bacteria, are extremely small. Our bodies contain 10 times more microbes cells than human cells.