Sandra Pizzarello¹, Laurence A. J. Garvie²

¹Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, USA
²Center for Meteorite Studies, Arizona State University, Tempe, Arizona, USA

Dicarboxylic acids were searched for in three Sutter’s Mill (SM) fragments (SM2 collected prerain, SM12, and SM41) and found to occur almost exclusively as linear species of 3- to 14-carbon long. Between these, concentrations were low, with measured quantities typically less than 10 nmole g⁻¹ of meteorite and a maximum of 6.8 nmole g⁻¹ of meteorite for suberic acid in SM12. The SM acids’ molecular distribution is consistent with a nonbiological origin and differs from those of CMs, such as Murchison or Murray, and of some stones of the C2-ungrouped Tagish Lake meteorite, where they are abundant and varied. Powder X-ray diffraction of SM12 and SM41 show them to be dominated by clays/amorphous material, with lesser amounts of Fe-sulfides, magnetite, and calcite. Thermal gravimetric (TG) analysis shows mass losses up to 1000 °C of 11.4% (SM12) and 9.4% (SM41). These losses are low compared with other clay-rich carbonaceous chondrites, such as Murchison (14.5%) and Orgueil (21.1%). The TG data are indicative of partially dehydrated clays, in accordance with published work on SM2, for which mineralogical studies suggest asteroidal heating to around 500 °C. In view of these compositional traits and mineralogical features, it is suggested that the dicarboxylic acids observed in the SM fragments we analyzed likely represent a combination of molecular species original to the meteorite as well as secondary products formed during parent-body alteration processes, such as asteroidal heating.

Reference
Pizzarello S and Garvie LAJ (in press) Sutter’s Mill dicarboxylic acids as possible tracers of parent-body alteration processes. Meteoritics & Planetary Science
[doi:10.1111/maps.12264]
Published by arrangement with John Wiley & Sons

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K. H. Joy¹, I. A. Crawford^2,3, G. R. Huss⁴, K. Nagashima⁴ and G. J. Taylor⁴

¹School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK
²Department of Earth and Planetary Sciences, Birkbeck, University of London, Bloomsbury, London, UK
³The Centre for Planetary Sciences at UCL/Birkbeck, London, UK
⁴Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, USA

Lunar meteorite MacAlpine Hills (MAC) 88105 is a well-studied feldspathic regolith breccia dominated by rock and mineral fragments from the lunar highlands. Thin section MAC 88105,159 contains a small rock fragment, 400 × 350 μm in size, which is compositionally anomalous compared with other MAC 88105 lithic components. The clast is composed of olivine and plagioclase with minor pyroxene and interstitial devitrified glass component. It is magnesian, akin to samples in the lunar High Mg-Suite, and also alkali-rich, akin to samples in the lunar High Alkali Suite. It could represent a small fragment of late-stage interstitial melt from an Mg-Suite parent lithology. However, olivine and pyroxene in the clast have Fe/Mn ratios and minor element concentrations that are different from known types of lunar lithologies. As Fe/Mn ratios are notably indicative of planetary origin, the clast could either (1) have a unique lunar magmatic source, or (2) have a nonlunar origin (i.e., consist of achondritic meteorite debris that survived delivery to the lunar surface). Both hypotheses are considered and discussed.

Reference
Joy KH, Crawford IA, Huss GR, Nagashima K and Taylor GJ (in press) An unusual clast in lunar meteorite MacAlpine Hills 88105: A unique lunar sample or projectile debris? Meteoritics & Planetary Science
[doi:10.1111/maps.12270]
Published by arrangement with John Wiley & Sons

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Jacob B. Simon^1,2,4 and Philip J. Armitage^2,3

¹Department of Space Studies, Southwest Research Institute, Boulder, CO 80302, USA
²JILA, University of Colorado and NIST, 440 UCB, Boulder, CO 80309-0440, USA
³Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309, USA
⁴Sagan Fellow.

We investigate the strength of axisymmetric local pressure maxima (zonal flows) in the outer regions of protoplanetary disks, where ambipolar diffusion reduces turbulent stresses driven by the magnetorotational instability. Using local numerical simulations we show that in the absence of net vertical magnetic fields, the strength of turbulence in the ambipolar dominated region of the disk is low and any zonal flows that are present are weak. For net fields strong enough to yield observed protostellar accretion rates, however, zonal flows with a density amplitude of 10%–20% are formed. These strengths are comparable to those seen in simulations of ideal MHD disk turbulence. We investigate whether these zonal flows are able to reverse the inward radial drift of solids, leading to prolonged and enhanced concentration as a prelude to planetesimal formation. For commonly assumed mean surface density profiles (surface density Σ∝r^-1/2 or steeper) we find that the predicted perturbations to the background disk profile do not correspond to local pressure maxima. This is a consequence of radial width of the simulated zonal flows, which is larger than was assumed in prior analytic models of particle trapping. These larger scale flows would only trap particles for higher amplitude fluctuations than observed. We conclude that zonal flows are likely to be present in the outer regions of protoplanetary disks and are potentially large enough to be observable, but are unlikely to lead to strong particle trapping.

Reference
Jacob B. Simon JB and Armitage PJ (2014) Efficiency of particle trapping in the outer regions of protoplanetary disks. The Astrophysical Journal 784:15.
[doi:10.1088/0004-637X/784/1/15]

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S. Cikota¹, J. L. Ortiz², A. Cikota³, N. Morales² and G. Tancredi⁴

¹Physics Department, University of Split, Nikole Tesle 12, 21000 Split, Croatia
²Instituto de Astrofísica de Andalucía – CSIC, Apt 3004, 18008 Granada, Spain
³Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstr. 25/8, 6020 Innsbruck, Austria
⁴Observatorio Astronómico Los Molinos DICYT-MEC Cno. de los Molinos 5769, 12400 Montevideo, Uruguay

It is well known that some Main Belt asteroids show comet-like features. A representative example is the first known Main Belt comet 133P/(7968) Elst-Pizarro. If the mechanisms causing this activity are too weak to develop visually evident comae or tails, the objects stay unnoticed. We are presenting a novel way to search for active asteroids, based on looking for objects with deviations from their expected brightnesses in a database. Just by using the MPCAT-OBS Observation Archive we have found five new candidate objects that possibly show a type of comet-like activity, and the already known Main Belt comet 133P/(7968) Elst-Pizarro. Four of the new candidates, (315) Constantia, (1026) Ingrid, (3646) Aduatiques, and (24 684) 1990 EU4, show brightness deviations independent of the object’s heliocentric distance, while (35 101) 1991 PL16 shows deviations dependent on its heliocentric distance, which could be an indication of a thermal triggered mechanism. The method could be implemented in future sky survey programmes to detect outbursts on Main Belt objects almost simultaneously with their occurrence.

Reference
Cikota S, Ortiz JL, Cikota A, Morales N and Tancredi G (2014) A photometric search for active Main Belt asteroids. Astronomy & Astrophysics 562:A94.
[doi:10.1051/0004-6361/201321679]
Reproduced with permission © ESO

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