The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.

/pdf/mineralogy-and-petrology-of-comet-81p-wild-2-nucleus-samples-4lf7lrtxqd.pdf

Mineralogy and petrology of comet 81P/wild 2 nucleus samples

The ultrahighly nanoporous aerogel is recognized as a state of matter rather than as a functional material, because of its qualitative differences in bulk properties, transitional density and enthalpy between liquid and gas, and diverse chemical compositions. In this review, the characteristics, classification, history and preparation of the aerogel were introduced. More attention was paid to the sol-gel method for preparing different kinds of aerogels, given its important role on bridging the synthetic parameters with the properties. At last, preparation of a novel single-component aerogel, design of a composite aerogel and industrial application of the aerogel were regarded as the research tendency of the aerogel state in the near future.

/pdf/a-special-material-or-a-new-state-of-matter-a-review-and-2xi5cioewh.pdf

A Special Material or a New State of Matter: A Review and Reconsideration of the Aerogel

We report the relative abundances of 17 elements in the atmosphere of the white dwarf star GD 362, material that, very probably, was contained previously in a large asteroid or asteroids with composition similar to the Earth-Moon system. The asteroid may have once been part of a larger parent body not unlike one of the terrestrial planets of our solar system.

http://iopscience.iop.org/article/10.1086/522223/pdf

The Chemical Composition of an Extrasolar Minor Planet

Particles emanating from comet 81P/Wild 2 collided with the Stardust spacecraft at 6.1 kilometers per second, producing hypervelocity impact features on the collector surfaces that were returned to Earth. The morphologies of these surprisingly diverse features were created by particles varying from dense mineral grains to loosely bound, polymineralic aggregates ranging from tens of nanometers to hundreds of micrometers in size. The cumulative size distribution of Wild 2 dust is shallower than that of comet Halley, yet steeper than that of comet Grigg-Skjellerup.

http://science.sciencemag.org/content/sci/314/5806/1716.full.pdf

Impact features on Stardust : implications for Comet 81P/Wild 2 dust

The Stardust spacecraft returned cometary samples that contain crystalline material, but the origin of the material is not yet well understood. We found four crystalline particles from comet 81P/Wild 2 that were apparently formed by flash-melting at a high temperature and are texturally, mineralogically, and compositionally similar to chondrules. Chondrules are submillimeter particles that dominate chondrites and are believed to have formed in the inner solar nebula. The comet particles show oxygen isotope compositions similar to chondrules in carbonaceous chondrites that compose the middle-to-outer asteroid belt. The presence of the chondrulelike objects in the comet suggests that chondrules have been transported out to the cold outer solar nebula and spread widely over the early solar system.

/pdf/chondrulelike-objects-in-short-period-comet-81p-wild-2-4k63xt119i.pdf

Chondrulelike Objects in Short-Period Comet 81P/Wild 2

We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed (similar to 180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.

/pdf/elemental-compositions-of-comet-81p-wild-2-samples-collected-vls0gqjjee.pdf

Ilona Sitnitsky

Papers

Elemental Compositions of Comet 81P/Wild 2 Samples Collected by Stardust