Panspermia: |
Directed Panspermia
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Contents Introduction
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The mission will be illustrated by choosing a representative candidate, Rho Ophiuchus (distance = 520 ly), a cloud that forms long-lived low and medium mass stars. As described by Mezger [8] (figure 1), the overall cloud extends to about 50 ly as low density gas ( hydrogen atom density nH < 1E3 cm-3, (ie., < 1.7E-18 kg m-3)) of total mass » 3,000 M¤ (solar mass M¤ = 2E30 kg), and contains a 6x6 ly dense fragment with a density of 1E4 cm-3 and mass ~500 M¤ , containing 78 young stellar objects of low-mass dust-embedded or early accretion stage T Tauri stars. Within this cloud are four cores with diameters of » 1 ly and, densities of densities of 1E6 cm-3 (1.7E-15 kg m-3) and masses of 1 - 15 M¤ .One of these cores shows four protostellar condensations with radii of » 3E14 m, densities of 1E7 cm-3 (1.7E-14 kg m3) and masses of 0.4 to 3 M¤ . Dust temperatures in this region are 15 - 20 K. Small panspermia capsules captured in a protostellar condensation or about a young star in an accreting planetary system will become part of the dust in the system. The protostallar condensation free-falls in » 4E4 yr to cores with radii of 100 au and densities of 1E11 - 1E12 cm-3 (1.7E-10 - 1.7E-9 kg m-3), which collapses further during 1E5 - 1E6 yr into a 1E6 m thick, 100 au (about 1E13 m) radius dust ring [9], that comprises 0.01 M¤ (2E28 kg) (possibly up to 0.1 M¤ (2E29 kg)) mass about a 1 M¤ young T-Tari star, and has a temperature of T = 50 - 400 K at 1 au (consider 250 K) (with possible periodic heating over 1,000 K), and T = 250a-0.58 at other distances a (in au = 1.5E11 m units) [10]. In the ring, the dust accretes rapidly (in 1E3 - 1E4 periods of revolution) from micron-size grains to 1 - 10 km planetisimals; then, in about 1E5 years, to 1E3km radius, 1E21 kg runaway planetary seeds that developing into 1E23 kg planetoids; and in the next 1E8 years, to planets [10]. Most of the gas is ejected from the disk in 1E6 - 1E7 yr by bipolar outflow and stellar UV radiation [10]. A fraction of the residual materials accrete in a zone of several tens of au from the star to become 10 km diameter, 1E14 - 5E14 kg nuclei of 1E13 comets, most of which are expelled to interstellar space [11], except 1E11 - 1E12 comets with a total mass of 1E25 - 1E26 kg that are retained in the Oort cloud at 1.7E4 - 1E5 au. [12] Another about 1E23 kg materials form the Kuiper belt comets [13], and 1E22 form the main-belt asteroids [14]. Cometary mass ablating in transits maintains a Zodiacal dust cloud of 2.5E16 kg and mean lifetime of 1E5 yr by injecting at present, about 2E4 kg s-1 dust near the perihelion passes at <3.5 au [15]. Of this, 0.15 kg s-1, ie., a fraction of 1E-5, is collected by the Earth [16a]. At higher densities in the prebiotic period between 3 and 4 Gyr (1Gyr = 1E9 yr) ago, 1E17 kg of the cometary dust accreted onto the Earth in the form of 0.6 to 60 m m radius particles in which organic material can be preserved during atmospheric transit [2]. Similar to the Zodiacal dust collection efficiency, 1E-5 of the asteroid fragments produced by collisions eventually impacts on the Earth as meteorites [16b]. Both data suggest that 1E-5 of the objects in orbit within several au of a habitable planet are eventually collected. Altogether, the 1E17 kg material of cometary origin that was collected by the Earth in the early biotic period between 3 - 4 Gyr ago, constitutes about 1E-13 of the total 1 M¤ (2E30 kg) protostellar condensation, 1E-11 of the mass of the original accretion dust ring, and 1E-9 of the total present Oort cloud cometary mass. These data from our solar systems are used as models. These data are current, model-dependent estimates with uncertainties up to an order of magnitude, and respective figures may be of course different in other solar systems. |
