An Earth-Mars Transfer of Life:During the warm, wet Martian Noachian

Lee Bardon, The Centre for Interdisciplinary ScienceDr. John Bridges, Physics & Astronomy.

ABSTRACT:We evaluate the likelihood of a viable, impact-driven exchange of microorganisms between Earth and the warm, wet Noachian Mars of ~4.0-3.5 Ga. The evaluation is performed under three conceptual subsections: 1. Impact & Ejection, where an evaluation of the flux of asteroid and comet impacts on Earth and the subsequent ejecta is carried out via craterological analysis and impact modelling techniques. 2. The Interplanetary Phase, n-body simulations were conducted to track of the orbital paths of test particles ejected from 100 km above the Earth's surface. 655,362 particles were tracked and 0.0019% were found to collide with Mars over a 30, 000 year simulation period. 3. Arrival & Proliferation on Noachian Mars and an analysis of the subaqueous surface area of Noachian Mars. Our results indicate that between ~2x105 and ~8x106 potentially viable life-bearing meteorite exchanges occurred between Earth and Mars during~4.0-3.5 Ga.

Image from NASA/JPL

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INTRODUCTIONAstrobiological research is chiefly concerned with the origin and distribution of life in the universe. In this work, we investigate whether life, once established, may be successfully transferred between planets of a given system via impact-driven means. In doing so, we examine the specific case of meteorite transfers between Earth and Mars, during a time when Mars was warmer and wetter (Carr, 2006), and likely much more habitable (Grotzinger et al., 2014) to Earth life than it is today.

1. IMPACT & EJECTIONIn the 1980’s,the shergottite, nakhlite and chassignite (SNC) meteorites were determined to have originated from Mars (e.g. Marvin, 1983; Trieman et al., 2000), thus demonstrating that a natural interplanetary exchange of crustal materials can occur. In this section, we utilise the 2011 Lunar Impact Crater Database (Losiak et al., 2011) to constrain the history of impacts in the Earth-Moon region.

We use relative cratering rates to estimate the fraction of these impacts that occurred during Guided by the excellent analysis of Mileikowsky et al. (2000), we use the equations of the semi-empirical spall theory (Melosh, 1984; 1987) along with scaling laws to estimate the average dimensions of impacting comets (long and short period) and asteroids, and to constrain the flux of impact ejecta least likely to have been sterilized as a function of temperature and pressure.

3. LIFE ON MARSThe n-body simulations described above allowed us to determine that 0.0019% of the ejected material from Earth collides with Mars. As a final constraint, we estimate the subaqueous surface area of Noachian Mars, under the assumption that arriving Earth life is more likely to survive and proliferate if it lands in a region of abundant water. Conservatively, 0.01% of Mars was subaqueous, rising to 0.4% with less rigorous approach.

Figure 2: Top Left: The location of ejected particles at launch (black band). Particles ejected from outside the band area were calculated to be very unlikely to interact with Mars. Bottom Left: The same data in a 2D projection. Bottom Right: Number of particle collisions with Mars over integration time (years).

Figure 1: Top Left: Earth impacts during 4.0 – 3.5 Ga, in terms of Long/Short Period (LP/SP) comets and asteroids, according to crater diameter. Data obtained by scaling from Moon impact data collected by Losiak et al., (2011). Top Right: Cumulative number of fragments ejected per LP comet impact, according to impactor diameter, during 4.0 – 3.5 Ga. The fragments quantified are those ejected from the spall zone around the impact, meaning that they are likely to have experienced temperatures and pressures that modern extremophiles could have survived. Bottom Left/Right: The same data for SP comets and asteroids.

2. THE INTERPLANETARY PHASEOnce the flux of potentially biologically-relevant material from Earth is constrained, we proceed to estimate the collision probability of that material with the surface of Mars. This is achieved through the implementation of a gravitational n-body simulation in the symplectic integration software environment Mercury 6.2 (Chambers, 1999), and with the collaboration of C. Chavez and M. Reyes-Ruiz at UNAM. Adapting and updating the approach utilized in Reyes-Ruiz et al., (2012), we track the orbital evolution of 655,362 test particles ejected from Earth, over a 30,000 year period: deemed relevant to the survival of microorganisms against the most biocidal extremes of space.

CONCLUSIONConsolidating the data from the three separate subsections of this report, we estimate that, according to the analytical approach developed over the course of this project, to potentially viable life-bearing meteorite exchanges occurred between Earth and Mars during the Martian Noachian.

Figure 3: The location of open-basin lakes (white circles), possible large crater lakes (red circles: 1. Hellas Basin; 2. Argyre Planitia; 3. Isidis Basin) and the proposed Ma’adim Vallis highland lake (red rectangle) on Noachian Mars. Image adapted from Fassett & Head (2008).