¹N. G. Rudraswami, ¹M. Shyam Prasad, ^1,2S. Dey, ³J. M. C. Plane, ³W. Feng, ⁴S. Taylor
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa 403004, India
²Indian Institute of Technology, Roorkee, Uttarakhand 247667, India
³School of Chemistry, University of Leeds, Leeds LS2 9JT, UK
⁴Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755-1290, USA

We evaluate the heating of extraterrestrial particles entering the atmosphere using the comprehensive chemical ablation model (CABMOD). This model predicts the ablation rates of individual elements in a particle with a defined size, composition, entry velocity, and entry angle with respect to the zenith (ZA). In the present study, bulk chemical analyses of 1133 Antarctica micrometeorites (collected from the south pole water well) are interpreted using CABMOD. The marked spread in Fe/Si values in unmelted, partially melted, and melted micrometeorites is explained by the loss of relatively volatile Fe during atmospheric entry. The combined theoretical modeling and elemental composition of the micrometeorites (Mg/Si ratios) suggest that ~85% of particles have a provenance of carbonaceous chondrites, the remaining ~15% are either ordinary or enstatite chondrites. About 65% of the micrometeorites have undergone <20% ablation, while a further 20% have lost between 20% and 60% of their original mass. This has implications for understanding the micrometeorite flux that reaches the Earth’s surface, as well as estimating the pre-atmospheric size of the particles. Our work shows that the unmelted particles that contribute ~50% to the total micrometeorite collection on Earth’s surface have a small entry zone: ZA = 60°–90° if the entry velocity is ~11 km s−1, and ZA = 80°–90° for >11–21 km s−1.

Reference
Rudraswami NG, Shyam Prasad M, Dey S, Plane JMC, Feng W, Taylor S (2015) EVALUATING CHANGES IN THE ELEMENTAL COMPOSITION OF MICROMETEORITES DURING ENTRY INTO THE EARTH’S ATMOSPHERE. The Astrophysicla Journal 814, 78
Link to Article [http://dx.doi.org/10.1088/0004-637X/814/1/78]

¹M. Lemelin, ¹P.G. Lucey, ²G.A. Neumann, ²E.M. Mazarico, ³M.K. Barker, ¹A. Kakazu, ¹D. Trang, ⁴D.E. Smith, ⁴M.T. Zuber
¹Hawaii Institute of Geophysics and Planetology, Dept. of Geophysics and Geology, University of Hawaii at Manoa, 1680 East-West Rd, Honolulu HI
²Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20771
³Sigma Space Corporation, 4600 Forbes Blvd., Lanham MD 20706
⁴Dept. of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Ave. Cambridge, MA 02139

The Lunar Orbiter Laser Altimeter (LOLA) experiment on Lunar Reconnaissance Orbiter (LRO) is a laser altimeter that also measures the strength of the return pulse from the lunar surface. These data have been used to estimate the reflectance of the lunar surface, including regions lacking direct solar illumination. A new calibration of these data are presented that features lower uncertainties overall and more consistent results in the polar regions. We use these data, along with newly available maps of the distribution of lunar maria, also derived from LRO instrument data, to investigate a newly discovered dependence of the albedo of the lunar maria on latitude (Hemingway et al. 2015). We confirm that there is an increase in albedo with latitude in the lunar maria, and confirm that this variation is not an artifact arising from the distribution of compositions within the lunar maria, using data from the Lunar Prospector neutron spectrometer. Radiative transfer modeling of the albedo dependence within the lunar maria is consistent with the very weak to absent dependence of albedo on latitude in the lunar highlands; the lower abundance of the iron source for space weathering products in the lunar highlands weakens the latitude dependence to the extent that it is only weakly detectable in current data. In addition, photometric models and normalization may take into account the fact that the lunar albedo is latitude dependent, but this dependence can cause errors in normalized reflectance of at most 2 % for the majority of near-nadir geometries. We also investigate whether the latitude dependent albedo may have obscured detection of small mare deposits at high latitudes. We find that small regions at high latitudes with low roughness similar to the lunar maria are not mare deposits that may have been misclassified owing to high albedos imposed by the latitude dependence. Finally, we suggest that the only modest correlations among space weathering indicators defined for the lunar samples may be due to mixing of soils from distinct latitudes.

Reference
Lemelin M, Lucey PG, Neumann GA, Mazarico EM, Barker MK, Kakazu A, Trang D, Smith DE, Zuber MT (2016) Improved calibration of reflectance data from the LRO Lunar Orbiter Laser Altimeter (LOLA) and implications for space weathering. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.02.006]
Coypright Elsevier