Skip to main content# Delivery of water and volatiles to planets in the habitable zone in the Proxima Centauri system

**Acknowledgments**

**References**

Presentation #1126 in the session “Open Engagement Session B”.

Published onMar 17, 2021

Delivery of water and volatiles to planets in the habitable zone in the Proxima Centauri system

**The model and initial data used for calculations.** Schwarz et al. (2018) studied migration of exocomets in the Proxima Centauri system. Besides the exoplanet with a semi-major axis *a*_{b}=0.0485 AU located in a habitable zone, they also considered the exoplanet “*c*” with a semi-major axis *a*_{c} from 0.06 to up to 0.3 AU (for test calculations up to 0.7 AU). Kervella et al. (2020) and Benedict and McArthur (2020) considered that the semi-major axis *a*_{c} of the exoplanet “*c*” equals to 1.489±0.049 AU. In the first series of calculations, according to Kervella et al. (2020), I considered a star with a mass equal to 0.122 of the solar mass, and two exoplanets with the following semi-major axes and masses: *a*_{b}=0.0485 AU, *a*_{c}=1.489 AU, *m*_{b}=1.27*m*_{E} and *m*_{c}=12*m*_{E}, where *m*_{E} is the mass of the Earth. For the exoplanet “*b*”, the initial eccentricity *e*_{b} and initial inclination *i*_{b} were considered to be equal to 0, and the initial eccentricity *e*_{c} of the exoplanet “*c*” equaled to 0 or 0.1. Initial inclination of the exoplanet “*c*” was considered to be *i*_{c}=*e*_{c}/2=0.05 rad or *i*_{c}=*e*_{c}=0. For interest, I also considered *i*_{c}=152^{o}; such calculations characterize the case when orbits of planetesimals were inclined to the orbit of the exoplanet. In the second series of calculations, as in Benedict and McArthur (2020), I considered *a*_{b }= 0.04857 AU, *e*_{b }= 0.11, *m*_{b }= 1.17 *m*_{E}, *a*_{c }= 1.489 AU, *e*_{c }= 0.04, *m*_{c }= 7 *m*_{E}. I supposed *i*_{b }= *i*_{c }= 0. *m*_{c} is different in the two series. In both series of calculations, the densities of the exoplanets “b” and “*c*” were considered to be equal to densities of the Earth and Uranus, respectively. In different calculation variants, initial semi-major axes of planetesimals were in the range from *a*_{min} to *a*_{max}=*a*_{min}+0.1 AU, with *a*_{min} from 1.2 to 1.7 AU with a step of 0.1 AU. Initial eccentricities *e*_{o} of planetesimals equaled to 0 or 0.15 for the first series of calculations, and *e*_{o}=0.02 or *e*_{o}=0.15 for the second series. Greater initial eccentricities could be a result of the mutual gravitational influence of planetesimals. Initial inclinations of the planetesimals equaled to *e*_{o}/2 rad. 250 planetesimals were considered in each calculation variant. The motion of planetesimals and exoplanets was calculated with the use of the symplectic code from Levison and Duncan (1994). Considered time interval exceeded 20 Myr. Based on the obtained arrays of orbital elements of migrated planetesimals and exoplanets stored with a step of 100 yr, I calculated the probabilities of collisions of planetesimals with the exoplanets. The calculations were made similar to those in (Ipatov and Mather, 2003, 2004a-b; Ipatov, 2019a-b; Marov and Ipatov, 2018), which had been made for the planets of the Solar System, but for different masses and radii of a star and exoplanets. If the probability of a collision with an exoplanet for some planetesimal reached 1 with time (it was obtained for a few planetesimals), then for a later time this planetesimal did not considered for calculation of the mean probability for the calculation variant.

**Probabilities of collisions of planetesimals with the exoplanet “**** b**”

**Probabilities of collisions of planetesimals with the exoplanet “**** c**”. For the first series of calculations at

**Conclusions**. For the Proxima Centauri planetary system, most of planetesimals from the vicinity of the exoplanet “*c*” with a semi-major axis *a*_{c} of about 1.5 AU were ejected into hyperbolic orbits in 10 Myr. Some planetesimals could collide with this exoplanet after 20 Myr. Only one of several hundreds of planetesimals from the vicinity of this exoplanet reached the orbit of the exoplanet “*b” *with a semi-major axis *a*_{b}=0.0485 AU or the orbit of the exoplanet “*d*” with a semi-major axis *a*_{d}=0.029 AU, but the probability of a collision of such planetesimal (that reached the orbits) with the exoplanets *b* and *d* can reach 1, and the collision probability averaged over all planetesimals from the vicinity of the exoplanet “c” was ~10^{-3}. If averaged over all considered planetesimals from the vicinity of exoplanet “c”, the probability of a collision of a planetesimal with the exoplanet “*b*” or “*d*” is greater than the probability of a collision with the Earth of a planetesimal from the zone of the giant planets in the Solar System (which is less than 10^{-5} per one planetesimal). A lot of icy material could be delivered to the exoplanets “*b*” and “*d*”.

The work was carried out as a part of the state assignments of the Vernadsky Institute of RAS № 0137-2020-0004 and the author acknowledges the support of Ministry of Science and Higher Education of the Russian Federation under the grant 075-15-2020-780 (N13.1902.21.0039) “Theoretical and experimental studies of the formation and evolution of extrasolar planetary systems and characteristics of exoplanets”.

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