Sune G. Nielsen^a,b, Julie Prytulak^a,c, Bernard J. Wood^a and Alex N. Halliday^a

^aDepartment of Earth Sciences, University of Oxford, South Parks Road, OX1 3AN, Oxford, UK
^bDepartment of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
^cDepartment of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK

It has been argued that the stable isotopic composition of the element vanadium (V) provides a potential indicator of the effects high-energy irradiation early in Solar System development. Such irradiation would produce enrichment in the minor isotope, ⁵⁰V compared with the 400 times more abundant ⁵¹V (Gounelle et al., 2001 and Lee et al., 1998). Here we show that the vanadium isotopic composition of the silicate Earth is enriched in ⁵¹V by ~0.8‰ compared with carbonaceous and ordinary chondrites as well as achondrites from Mars and the asteroid 4 Vesta. Although V is depleted by core formation, experiments reveal no isotopic fractionation between metal and silicate that could account for the observed difference in V isotope composition between terrestrial and extraterrestrial materials. Nucleosynthetic provenance of the terrestrial vanadium isotope offset is inconsistent with anomalies of other nucleosynthetically produced isotopes in bulk meteorites, which are more variable than vanadium (Burkhardt et al., 2011, Carlson et al., 2007 and Trinquier et al., 2009). Furthermore, V isotopes are unlikely to have been affected by volatilization, parent body alteration or impact erosion of Earthʼs surface. Therefore, the cause of the isotopic difference is unclear. One possibility is that Earthʼs isotopically heavier V reflects a deficit in material irradiated during the initial stages of Solar System formation. Whatever the cause, the terrestrial deficit in ⁵⁰V implies that bulk Earth cannot be entirely reconstructed by mixtures of different meteorites.

Reference
Nielsen SG, Prytulak J, Wood BJ and Halliday AN (2014) Vanadium isotopic difference between the silicate Earth and meteorites. Earth and Planetary Science Letters 389:167–175.
[doi:10.1016/j.epsl.2013.12.030]
Copyright Elsevier

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David A. Minton^a and Harold F. Levison^b

^aPurdue University Department of Earth, Atmospheric, & Planetary Sciences, 550 Stadium Mall Drive, West Lafayette, IN 47907
^bSouthwest Research Institute and NASA Lunar Science Institute, 1050 Walnut St. Suite 300, Boulder, CO 80302

We develop a model for planetesimal-driven migration (PDM) in the context of rocky planetary embryos in the terrestrial planet region during the runaway and oligarchic growth phases of inner planet formation. We develop this model by first showing that there are five necessary and sufficient criteria that must be simultaneously satisfied in order for a rocky inner solar system embryo to migrate via PDM. To investigate which embryos within a given disk satisfy the five criteria, we have developed a Monte Carlo planetesimal merger code that simulates the growth of embryos from a planetesimal disk with nebular gas. The results of our Monte Carlo planetesimal merger code suggest that, for typical values of the minimum mass solar nebula for the inner solar system, an average of 0.2 embryos capable of PDM emerge over the lifetime of the disk. Many disks in our simulations produce no migration candidates, but some produced as many as 3. The number of embryos that experience PDM in a disk increases with increasing disk mass and decreasing il planetesimal mass, although we were not able to simulate disks where the average initial planetesimal size was smaller than 50 km. For disks 4× more massive than the standard minimum mass solar nebula, we estimate that an average of 1.5 embryos capable of PDM emerge, with some producing as many as 7.

Reference
Minton DA and Levison HF (2014) Planetesimal-driven migration of terrestrial planet embryos. Icarus
[doi:10.1016/j.icarus.2014.01.001]
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Y.-M. Lim¹, K.-W. Min¹, P. D. Feldman², W. Han³, and J. Edelstein⁴

¹Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Korea
²Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
³Korea Astronomy and Space Science Institute (KASI), 776 Daedeokdae-ro, Yuseong-gu, Daejeon 305-348, Korea
⁴Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, USA

We present the results of far-ultraviolet observations of comet C/2001 Q4 (NEAT) that were made with the Far-Ultraviolet Imaging Spectrograph on board the Korean satellite STSAT-1. The observations were conducted in two campaigns during its perihelion approach between 2004 May 8 and 15. Based on the scanning mode observations in the wavelength band of 1400-1700 Å, we have constructed an image of the comet with an angular size of 5°×5°, which corresponds to the central coma region. Several important fluorescence emission lines were detected including S I multiplets at 1429 and 1479 Å, C I multiplets at 1561 and 1657 Å, and the CO A¹Π-X¹Σ⁺ Fourth Positive system; we have estimated the production rates of the corresponding species from the fluxes of these emission lines. The estimated production rate of CO was Q_CO = (2.65 ± 0.63) × 10²⁸ s^-1, which is 6.2%-7.4% of the water production rate and is consistent with earlier predictions. The average carbon production rate was estimated to be QC  = ~1.59 × 10²⁸ s^-1, which is ~60% of the CO production rate. However, the observed carbon profile was steeper than that predicted using the two-component Haser model in the inner coma region, while it was consistent with the model in the outer region. The average sulfur production rate was QS  = (4.03±1.03) × 10²⁷ s^-1, which corresponds to ~1% of the water production rate.

Reference
Lim Y-M, Min K-W, Feldman PD, Han W and Edelstein J (2014) Far-ultraviolet Observations of Comet C/2001 Q4 (NEAT) with FIMS/SPEAR. The Astrophysical Journal 781:80.
[doi:10.1088/0004-637X/781/2/80]

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