Enhanced interplanetary panspermia in the TRAPPIST-1 system

Abstract

We present a simple model for estimating the probability of interplanetary panspermia in the recently discovered system of seven planets orbiting the ultracool dwarf star TRAPPIST-1 and find that panspermia is potentially orders of magnitude more likely to occur in the TRAPPIST-1 system compared with the Earth-to-Mars case. As a consequence, we argue that the probability of abiogenesis is enhanced on the TRAPPIST-1 planets compared with the solar system. By adopting models from theoretical ecology, we show that the number of species transferred and the number of lifebearing planets are also likely to be higher because of the increased rates of immigration. We propose observational metrics for evaluating whether life was initiated by panspermia on multiple planets in the TRAPPIST-1 system. These results are also applicable to habitable exoplanets and exomoons in other planetary systems.exoplanets | panspermia | origin of life | astrobiology T he field of exoplanetary research has witnessed remarkable advances in the past two decades, with the total number of discovered exoplanets now numbering in the thousands (1). This progress has been accompanied by a better understanding of the factors that make a planet habitable (i.e., capable of supporting life) (2). It is now well-known that there exist ∼ 10 10 habitable planets in the Milky Way, many of which orbit M dwarfs (3). Planets in the habitable zone (HZ)-the region theoretically capable of supporting liquid water-of M dwarfs have been extensively studied, because they are comparatively easier to detect and analyze (4).The search for exoplanets around nearby low-mass stars has witnessed two remarkable advances over the past year, namely (i) the discovery of Proxima Centauri b, the nearest exoplanet to the solar system (5), and (ii) the discovery of seven planets transiting the ultracool dwarf star TRAPPIST-1 (6). The latter is all of the more remarkable, because three of seven planets reside within the HZ; also, each of them has a mass and a radius that are nearly equal to those of the Earth (7). Hence, the TRAPPIST-1 transiting system represents a unique opportunity for carrying out additional observations to determine whether these planets possess atmospheres and perhaps, even biosignatures (8).If conditions favorable for the origin of life (abiogenesis) exist on one of the TRAPPIST-1 planets, this possibility raises an immediate question with profound consequences: could life spread from one planet to another (panspermia) through the transfer of rocky material? Panspermia has been widely investigated in our own solar system as a potential mechanism for transporting life to or from the Earth (9-13). The planets in the HZ of the TRAPPIST-1 system are separated only by ∼ 0.01 a.u., tens of times less than the distance between Earth and Mars. Thus, one would be inclined to hypothesize that panspermia would be enhanced in this system.Here, we explore this possibility by proposing a simple quantitative model for panspermia within the TRAPPIST-1 system. We show that ...

Colloquium: Physical constraints for the evolution of life on exoplanets

“…In addition, planets may have formed outside the HZ and escaped the brunt of the long and intense pre-main-sequence phase of M-dwarfs, before eventually migrating inwards into the HZ at a later stage; see Tamayo et al (2017) and Ormel et al (2017). Finally, M-dwarf planetary systems might possess inherent advantages such as the enhanced transport of life between planets via lithopanspermia by several orders of magnitude compared to the Earth-Mars system (Steffen and Li, 2016;Lingam and Loeb, 2017c;Krijt et al, 2017). However, in each of the above instances, either a high degree of fine tuning might be required or the feasibility of the proposed mechanisms remains indeterminate.…”

Hydrocode modeling of the spallation process during hypervelocity impacts: Implications for the ejection of Martian meteorites

“…This has a wide range of implications, not only for the acceleration of Martian meteorites, but also for material exchange amongst planetary bodies in satellite systems, including the Earth-Moon, Mars-satellites, Jovian, Saturnian, and Pluto-Charon systems [e.g., Artemieva and Ivanov, 2004;Artemieva and Lunine, 2005;Stern, 2009;Chappaz et al, 2013;Ramsley and Head, 2013;Porter and Grundy, 2014]. In addition, our numerical models may have astrobiological implications, such as for the Panspermia [e.g., Melosh, 2003;Burchell et al, 2003;Price et al, 2013;Krijt et al 2017;Lingam and Loeb, 2017].…”

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“…In order to detect worlds that are rendered habitable by radiogenic and primordial heating, the spectral flux density (S) received at Earth via black body emission must be sufficiently high (see Abbot & Switzer 2011). 4 S is determined by scaling the black body spectral ra-3 Note that the prospects for interplanetary panspermia are enhanced for clustered planetary systems such as those around Mdwarfs (Lingam & Loeb 2017). 4 In some respects, our analysis is similar to the detection of freefloating Y-type brown dwarfs (Burrows et al 2003;Biller 2017), because they have black body temperatures as low as ∼ 250 K.…”