Molteno meteorite, Enoch Mgijima Local Municipality, Chris Hani District Municipality, Eastern Cape, South Africai

Regional Level Types
Molteno meteorite	Meteorite Fall Location
Enoch Mgijima Local Municipality	Municipality
Chris Hani District Municipality	Municipality
Eastern Cape	Province
South Africa	Country

Howardite (HED achondrite)
Fell, April or May 1953; 150 g

After detonations a small stone with an unusual two-component fusion crust was recovered, one of the only 16 witnessed Howardite falls of the 19th and 20th centuries. Howardites are breccias composed primarily of fragmented Eucritic and Diogenitic materials assembled from both crustal and plutonic regions, respectively, on one or more ancient large asteroids. Thus, unsurprisingly, Molteno contains variable pyroxenes (>90 vol%), plagioclase (~5 vol%, sometimes intergrown with troilite), and several other minor silicates and opaques. In this particular case, Molteno consist primarily of Diogenitic pyroxenites mingled with a significant quantity of accessory Eucritic clasts (plagioclase-pyroxene). An extra boon — especially in such a small stone — is that Molteno contains small quantities of quite variable olivine. This suggests the intriguing possibility that Molteno may contain components from a deeper source within the first homeworld than even the orthopyroxene-rich Diogenites.

Over the past four decades contemporary planetary scientists have combined astronomical and mineralogical findings and have gradually concluded that the brightest asteroid, 4 Vesta is the Original Planet Body (OPB) for most or even almost all of the HED meteorites (Howardites-Eucrites-Diogenites). And combining the mineralogical information referenced here with findings from the recently completed DAWN Spacecraft Mission to Vesta, we might reasonably expect that Vesta would indeed be Molteno's Original Planet Body.

A caveat. Recent studies — including new very high-resolution O-isotope findings — have also presented seemingly irrefutable evidence that several HED meteorites are not fragments from the same OPB as most 'normal' HEDs. (Most notable are a few 'anomalous' Eucrites). For now, at least, we must wait a little longer before we can definitively assign Molteno and/or other HED meteorites to Vesta or some other presently unidentified original homeworld.

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References