Free Astronomy Magazine November-December 2017

11 NOVEMBER-DECEMBER 2017 SOLAR SYSTEM moved in 2 million years), with the external presence of a virtual Jupiter and Sat- urn in low-eccentricity or- bits, held together by a 3:2 resonance, with Jupiter 5.4 AU from the Sun. The inner area of planetary formation included 2 to 2.5 Earth masses, distributed between 0.7 and 1 AU, or 0.7 and 1.5 AU (each simulation had different initial configura- tions). Those masses were di- vided between 50 and 100 planetary embryos, in addi- tion to a cluster of 2000- 5000 100-km-sized planetesi- mals. The planetary embryos made up between 75% and 90% of the total mass. The gravitational disturbance due to the growth of the vir- tual rocky objects gradually dispersed the ring outwards, and in this scenario Mars would be a large embryo ex- pelled from the ring (following gravita- tional interactions with its peers) and thus deprived of a way to gain further mass. The simulations Raymond and Izidoro ran O n the right, semimajor axis–eccentricity and inclination distribution of S- type asteroids im- planted from the terrestrial planet region. All plan- etesimals from the end of the simulations are shown, and the implanted ones are solid. The shaded region represents the main asteroid belt, defined here as having perihe- lion distance q > 1.8 AU, eccentric- ity e < 0.3, and in- clination i < 25°. [S.N. Raymond, and A. Izidoro] Below, Sean N. Raymond, first author of the new study. finally produced Earth-like planets broadly resembling the real ones in our solar sys- tem, and the eccentricities and inclinations of their orbits are consistent with the real ones. It is doubtless a good starting point to test what could have happened to the planetesimals from the ring that were still in circulation after the planetary forma- tion. The researchers ob- served that their virtual masses were disseminated in orbits that intersect the area now occupied by the main asteroid belt (but ini- tially empty in the simula- tions). Simple transits of planetesimals in that area would not, however, have prevented the Sun’s gravity from attracting those ob- jects, sooner or later making them slam into the young, rocky planets. But the simu- lations indicate that if the belt had been repeatedly crossed by a planetary em- bryo as well, it could have