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In the pursuit of regolithic howardites
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Mittlefehldt, David W. Quinn, J. E. Herrin, J. S. Cartwright, J. A. Mertzman, K. R. Peng, Z. X. Ott, U. Mertzman, S. A. |
| Copyright Year | 2012 |
| Description | The HED (Howardite, Eucrite and Diogenite) meteorite clan likely originate from the asteroid 4-Vesta [1]. Howardites (polymict breccias of eucritic and diogenitic material) are believed to originate from the vestan surface, and many contain regolith-like features (impact and/or melt clasts, fragmental breccia clasts, carbonaceous chondrite fragments), which may relate to regolith-formation processes. Noble gas analysis can help determine true regolithic nature, as Solar Wind (SW) is im-planted into grains at the upper-surfaces of solar system bodies lacking an atmosphere or magnetic field. Howardites from Ves-ta s true regolith would thus show evidence for SW components. Thus far, we have identified 5 regolithic howardites: LEW 85313; MET 00423; PRA 04401; SCO 06040 and EET 87513; based on our noble gas analyses, with the latter 3 showing some evidence for a planetary(+SW) component, likely related to CM-like material present in the assemblage [2-5]. However, we did not find a good correlation between SW content and other petro-logic regolithic features. Nor did we find an obvious correlation between SW and high siderophile element contents (Ni greater than 300 micrograms/gram), or an Al2O3 range of 8-9 wt% and eucrite/diogenite (E/D) ratio of 2:1 as suggested by [6] to be further regolith indicators. Here, we report our latest noble gas data for two howardites GRO 95535, GRO 95602 and a polymict eucrite EET 87518 in continuing research aimed at better understanding the vestan regolith. Results: Noble gas analysis was performed on an MAP 215-50 noble gas mass spectrometer using furnace step-heating. Our results, shown in Table 1, are compared with SW- (LEW 85313) and planetary-dominated (PRA 04401 ~60% CM) howardites [2]. EET 87518 is dominated by cosmogenic components. By comparison, both howardites show strong evidence for SW, with total Ne-20/Ne-22 ~8.7-8.8 (SW: Ne-20/Ne-22 13.78 [7]), and identical release patterns to our other CM-poor SW-rich samples. This suggests that these samples are from the vestan regolith. As they have lower Ni contents than suggested by [6], this further illustrates that these parameters may show some bias [2]. |
| File Size | 103335 |
| Page Count | 1 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_20120011567 |
| Archival Resource Key | ark:/13960/t9479ct71 |
| Language | English |
| Publisher Date | 2012-08-12 |
| Access Restriction | Open |
| Subject Keyword | Lunar And Planetary Science And Exploration Vesta Asteroid Meteorites Meteoritic Composition Neon Isotopes Nickel Gas Spectroscopy Regolith Breccia Solar Wind Achondrites Rare Gases Aluminum Oxides Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
