Meteorites

• Meteorites are also concentrated in hot deserts such as North Africa, Northwest Africa (NWA), Chile – Atacama Desert, USA, and Australia.
• Meteorites are observed to fall from the sky or are witnessed as a fireball.
• Fireballs associated with falls allow us to track the trajectory and determine the source of a meteorite.
• Meteorites are affected by terrestrial weathering from the moment they land, with weathering of metal and silicate minerals and contamination by terrestrial water and organic material.
• The importance of finds is to determine the historical flux record and provide a wider diversity of meteorite types.
• Explosions in the atmosphere produce shock waves at the surface, as seen in the Tunguska event in Russia in 1908, where a forest area of 2000 km 2 was flattened (60 million trees).
• The largest meteorite is Hoba, found in Namibia, which fell about 80,000 years ago and weighs about 60 tons.
• Ice sheets collide with the Trans Antarctic Mountain Range where they well up and are ablated by the wind, resulting in the concentration of meteorites on the blue ice field.
• The Peeksgill meteorite, which fell on 9th October 1992, weighed 12.5 kg and was a H6 chondrite.
• The main mass of the Lake Chebarkul meteorite is 654 kg.
• Meteorites are found some time after fall, up to millions of years.
• In January 2022, there had been 1,214 witnessed falls of meteorites.
• Small projectiles (< a few meters) lose their original velocity and kinetic energy in the atmosphere, strike the ground at < ~100 m/s, excavate a pit slightly larger than the projectile itself, and survive within the pit.
• The Chelyabinsk meteor occurred on in 2013, with a meteor size of 15-20 m diameter, meteor mass of 7,000-10,000 tonnes, entry velocity of 19 km/sec, airburst altitude of 25 km, and energy released of 500 kton.
• Hayabusa returned from asteroid Itokawa in 2010 with approximately 2000 dust particles, most less than 100 m m, and a total mass of less than 100 g.
• Missions to the Moon include Apollo, Luna, and Chang’e 5.
• OSIRIS-REx is a mission to asteroid Bennu.
• Three asteroids were visited by Hayabusa, asteroid Itokawa, and Hayabusa2, asteroid Ryugu.
• Meteorite samples are available from the Moon, Mars, numerous asteroids, and numerous comets.
• Hayabusa2 returned from asteroid Ryugu in 2020 with a total mass of 5.4 g.
• Extraterrestrial samples for laboratory study are available from spacecraft missions to the Moon, comets, asteroids, and the solar system.
• Interplanetary Dust Particles (IDPs) are collected on high-altitude aircraft and have a total mass of less than 1 g.
• Micrometeorites are sub-millimetre dust particles, estimated to be around 3000 tonnes/year falling to Earth, with a total recovered mass very small.
• The total number of named meteorites is 69,140, with Antarctic meteorites contributing 43,339, Northwest Africa contributing 10,623, Australia contributing 720, USA contributing 1,888, China contributing 444, Chile contributing 2,190, UK contributing 23 (19 are falls), and other countries contributing 1.
• Stardust returned from Comet Wild II in 2006 with approximately 1000 particles, each less than 100 m m across, and a total mass of less than 1 mg.
• OSIRIS-REx is a mission to asteroid Bennu with a sample return planned for 2023, and its total mass is expected to be greater than 70 g.
• Ordinary chondrites are a type of chondrites with 48,662 falls and 899 finds.
• Enstatite chondrites are a type of chondrites with 598 falls and 17 finds.
• Barringer (Meteor) Crater, Arizona, is a 1.2 km diameter impact crater that is 49,000 years old.
• Irons are a type of achondrites with 500 falls and 20 finds.
• Irons are a type of chondrites with 1,151 falls and 49 finds.
• Lunar meteorites are a type of chondrites with 290 falls and 0 finds.
• Total number of chondrites is 56,296 with 1,152 finds.
• Total number of achondrites is 1,547 with 320 finds.
• Chondrites are meteorites that represent the parent asteroids that never melted.
• Martian meteorites are a type of chondrites with 188 falls and 5 finds.
• Pallasites are a type of chondrites with 110 falls and 4 finds.
• “HED” (Vesta) Basalts are a type of chondrites with 1,866 falls and 64 finds.
• Achondrites are meteorites that represent asteroids that were once melted.
• Chondrites are the most common type of meteorites, with 51,648 falls and 967 finds.