We must send robots and people to the most promising places to search for life on Mars
Cite as: Spacek, J. (2022) “How to Search for Life on Mars” Primordial Scoop, e20220421. https://doi.org/10.52400/BPUX8738
This post provides additional discussion and references for How to Search for Life on Mars (Robert Zubrin, Steven Benner, and Jan Špaček, submitted to Scientific American)
Central to any claim that human-engineered transfer of material from Mars to Earth or Earth to Mars creates a planetary protection risk is the premise that such human-engineered transfer is novel, that is, it does not occur naturally. As noted in the Scientific American piece, natural transfer occurs frequently. Further, because of the interest in panspermia, a large number of studies have simulated this process. This adds to empirical data (we can pick up Martian rocks from the tops of desert dunes and Antarctic glaciers that have scarcely been heated on their voyage from Mars to Earth) that allows us to estimate directly the amount of material (500 kg) that comes from Mars to Earth each year (including last year). Additional reading is provided below.
Mars-to-Earth material transfer
Martian rocks are (from geological perspective) frequently ejected from the Martian surface by impact events on Mars. Some of the ejected material finds its way to Earth, were we can find it as a Martian meteorites. So far we have identified over 270 Martian meteorites here on Earth, among which the “Black Beauty” is one of the most famous. For more information about Martian meteorites, see this recent review:
Udry, A., Howarth, G. H., Herd, C. D. K., Day, J. M., Lapen, T. J., & Filiberto, J. (2020). What Martian meteorites reveal about the interior and surface of Mars. DOI: doi.org/10.1029/2020JE006523
This Wikipedia article distills this information for the layperson.
Earth-to-Mars material transfer
Transfer of material from Earth-to-Mars is less frequent because:
(1) Earth has stronger gravity, requiring ejected material to travel faster (escape velocity on Earth is 11.19 km/sec, Mars escape velocity is 5.03 km/sec).
(2) Material ejected from any planetary body into the Solar System is more likely to travel towards the Sun than away from the Sun.
(3) Earth has thicker atmosphere than Mars, at least recently, and this demands a higher kinetic-energy-to-drag ratio of the ejected material. This problem is partially mitigated by “holes” in the atmosphere created by ~10 km asteroids or comets. These take minutes to fill, while the ejected material traveling over 11.2 km/sec takes only few seconds to escape the atmosphere.
Nevertheless, there are many historical impacts large enough to eject material from Earth with higher than escape velocity. See:
Wallis, M. K., & Wickramasinghe, N. C. (1995). Role of major terrestrial cratering events in dispersing life in the Solar System. Earth and Planetary Science Letters, 130(1-4), 69-73.
Melosh, H. J. (1988). The rocky road to panspermia. Nature, 332(6166), 687-688.
And many of these are predicted to land on Mars:
Worth, R. J., Sigurdsson, S., & House, C. H. (2013). Seeding life on the moons of the outer planets via lithopanspermia. Astrobiology, 13(12), 1155-1165.
The 2022 official NASA policy according to NASA administrator Bill Nelson, ‘State of NASA’ Address:
- Humans will walk on Mars by 2040 (21:15)
- Humans on the surface are essential for the search for life on Mars (21:22)
- Still, the samples from Mars will be brought to the Moon first, instead of to Earth (23:30)
One of the authors of the Scientific American piece provides more detailed discussion.
Robert Zubrin, Richard Wagner, The Case for Mars: The Plan to Settle the Red Planet and Why We Must, Simon and Schuster, New York, 1996, 2011, 2021.
Robert Zubrin, “The Mars Decision,” The New Atlantis, Fall 2019 https://www.thenewatlantis.com/publications/the-mars-decision (accessed April 20, 2022)
Robert Zubrin, “President Biden Should Push for the Human Exploration of Mars,” Scientific American, March 25, 2021. https://www.scientificamerican.com/article/president-biden-should-push-for-the-human-exploration-of-mars/ (accessed April 20, 2022)
