The largest meteorite we know of was found in 1920 in South West Africa, now Namibia. It was found, by pure chance, Michael Hanssenowner of a farm called Hoba West near the town of Grootfontein. While working with the plow, it got stuck in the ground and Hanssen heard a metallic noise. Here emerged from the earth the Hoba meteoritewhich still today holds the record for the largest and most massive meteorite ever found, with a tonnage of well 66 tons (now reduced to 64 due to numerous withdrawals that have occurred over the years).
The meteorite is still located exactly where it was found, i.e. approximately where it fell 80,000 years ago: the surrounding land was excavated and circular steps were created around the celestial body. From the 1955 it was declared a national monument to protect it from those who detached fragments, and is visited by thousands of tourists every year who can touch first-hand what remains of a celestial body as old as the Solar System (i.e. about 4.5 billion years!).
Composition and characteristics of the Hoba meteorite
The Hoba meteorite is essentially a single block of iron (84%) e nickel (16%). It is therefore an iron meteorite, to be precise aataxitethe type of meteorite with the highest abundance of nickel. It is therefore probably the central nucleus of an ancient asteroid. This is the largest mass of iron known on planet Earth!
It has a rather unusual shape, reminiscent of a parallelepiped, with an approximately square base on the side 2.7 meters and a height of 90 centimetres. It was precisely its very “robust” composition that allowed it to retain its considerable dimensions even after impact with the ground.
The enigma of the absence of an impact crater
The biggest enigma linked to the Hoba meteorite, however, is the total lack of an impact crater: how did such a beast fall to the ground without apparently leaving a clear trace on the ground? Scientists don’t know for sure, but it’s likely the meteorite has slowed down significantly during the last stages of the fall, so much so as not to create a crater. But how did he slow down so much? It is possible that its peculiar, somewhat “disc-like” shape contributed: if it had entered the atmosphere with an almost horizontal trajectory, it could have bounced in the air a bit like a stone thrown quickly and “edged” onto a pond, thus allowing the celestial body to reduce its speed before falling to the ground.
