Aguas Zarcas 10°23’29.03"N, 84°20’28.58"W
Alajuela, Costa Rica
Confirmed fall: 2019 Apr 23
Classification: Carbonaceous chondrite (CM2)
History: (G.J. Soto; P. Madrigal,
O. Lücke, Escuela Centroamericana de Geología, Universidad de Costa
Rica; M. Farmer, Arizona) At 21:07 local time on 23 April 2019, a
meteorite fall was reported in Aguas Zarcas, San Carlos county, Alajuela
province, Costa Rica. The fireball traveled WNW to ESE and was caught
on cameras of the National Seismological Network (RSN) at the summit of
Poás and Turrialba volcanoes, and from the Volcanological and
Seismological Observatory of Costa Rica (OVSICORI). Sightings were
reported from Quepos (Central Pacific) in the south and north to La
Palmera in San Carlos. The first piece recovered, 1152 g, crashed
through a house at 10°23’29.03"N, 84°20’28.58"W. A dog house was hit by a
280 g piece at 10°24’9.35"N 84°21’51.26"W. The BRAMON (Brazilian
Meteors Observation Network), UNESP (São Paulo State University) and USP
(University of São Paulo) teams determined the atmospheric trajectory
of the bolide from four security videos and dashcam cameras. The bolide
had an entry angle of 73° relative to the ground, traveling 20.7 km in
the 4-s analyzed interval, with an atmospheric velocity of 14 km/s.
Analysis shows a projected elliptical strewn-field with major axis
length of 6.3 and minor axis of 3.3 km. Hundreds of stones were
recovered within the projected strewn-field. The bolide orbit was
determined, with the follow preliminary elements: semi-major axis 2.7
AU, eccentricity 0.63, inclination 3.09°, pericenter longitude of 185.3°
and ascending node 33.4°. Current total recovered mass is around 27 kg,
of which ~11 kg was collected before rain fell over the fall site.
Physical characteristics: (L. Garvie, ASU)
Hundreds of fusion-crusted stones ranging from 0.1 to 1868 g. Stones
under ~50 g are typically angular to blocky and lack regmaglypts. Also
found were several plate-like, oriented stones. For example, one
oriented plate is 13 cm wide and 1 cm thick. Many stones are oriented
with a domed leading edge and well-developed roll-over lip along the rim
of the trailing edge. Larger stones, especially those near 1 kg, show
broad regmaglypts, some well developed. The fusion crust on several of
the trailing edge surfaces is iridescent. Pre-rain material crushed in a
few ml of water emits a powerful "Murchison-like" odor, though with a more prominent compost-like scent.
Petrography: (L. Garvie, ASU)
The interior of the stones is uniformly dark gray and studded with
small light-colored speckles. Stones are brecciated and dominated by two
lithologies: chondrule poor, constituting ~80 areal% of the broken
surfaces examined (~2 kg of material), and chondrule rich. Chondrules
constitute ~10 areal% of the chondrule-poor lithology and ~40 areal% in
the chondrule-rich lithology. Some broken surfaces show clasts of the
chondrule-rich lithology in the chondrule-poor type. Clasts with lower
chondrule to matrix ratio also present; for example, one 3 g half stone
shows <1 areal% chondrules. A probe mount of the dominant
chondrule-poor lithology (sample area 1.5 × 2.2 cm) shows scattered
small chondrules (mean 275 μm, n=40), with prominent fine-grained rims.
Rare chondrules to 2 mm. Fe-Ni metal, which is Cr-bearing, was only
found as rounded grains in one 100-μm type I chondrule. The section
contains several Al-rich CAIs to 300 μm. The matrix is dominated by two
components of roughly equal proportions: anhedral clumps (typically 50
microns) that are Fe and S rich (e.g., 37.5 wt% Fe and 5.8 wt% S, with
microprobe total of 93%), surrounded by fine-grained material poorer in
Fe and S (e.g., 12.8 wt% Fe, 13.9 wt% Mg, and 0.5 wt% S, with microprobe
total of 80.0%). Powder XRD from five stones (one chondrule rich) shows
patterns dominated by serpentine. In two stones, the serpentine 001
reflection sits on a broad peak centered at 0.843 nm. Reflections for
tochilinite and calcite occur in all patterns. The intensities of
olivine and pyroxene reflections were generally low, but most prominent
in the chondrules-rich stone.
Geochemistry: Oxygen isotopes (K. Ziegler, UNM): 7 pre-rain fragments analyzed by laser fluorination gave δ18O= 10.342, 10.807, 11.591, 12.314, 12.249, 12.669, 9.748; δ17O= 2.381, 2.932, 3.360, 3.843, 3.995, 3.959, 2.143; Δ17O=-3.080, -2.775, -2.759, -2.659, -2.472, -2.730, -3.004 (linearized, all per mil, TFL slope=0.528). Microprobe (L. Garvie, ASU): Fa0.4-41.0, n=10.
Classification: Geochemistry and oxygen isotopic data consistent with CM2.
Specimens: 248 g ASU; MFarmer - 6.5 kg; Achim Karl - 2.5 kg; Robert Ward - 3.2 kg; Kevin Kichinka - 489 g.