As part of the hands on experience for the first year astronomy course, a real meteorite and various meteorite fragments were brought in astronomy class on Tuesday, December 1st. This way the students had the change to touch and examine a variety of space meteorite fragments, which fell in various places on the Earth. In particular, they examined an approximately 1 kg stony meteorite that fell in Dhofar dessert in Oman which still remains to be classified, as well as a meteorite fragment that originate on asteroid Vesta, which is the second-most-massive body in the asteroid belt after the dwarf planet Ceres, and has a diameter of 525 km.
Furthermore, they examined a fragment that originated from the meteorite that fell in Russian on February 15th, 2013. The Chelyabinsk meteor was a superbolide caused by a near-Earth asteroid that entered Earth's atmosphere over Russia on 15 February 2013 at about 09:20 (03:20 UTC), with a speed of 19.16 ± 0.15 km/s. The light from the meteor was brighter than the Sun, up to 100 km away. It was observed over a wide area of the region and in neighbouring republics. The explosion generated a bright flash, producing a hot cloud of dust and gas that penetrated to 26.2 km, and many surviving small fragmentary meteorites, as well as a large shock wave. The bulk of the object's energy was absorbed by the atmosphere, with a total kinetic energy before atmospheric impact equivalent to approximately 500 kilotons of TNT, 20-30 times more energy than was released from the atomic bomb detonated at Hiroshima. With an estimated initial mass of about 12,000-13,000 metric tonnes, and measuring about 20 metres in diameter, is the largest known natural object to have entered Earth's atmosphere since the 1908 Tunguska event. This meteorite has been mainly classified as an ordinary chondrite. First estimates of its composition indicate about 10% of meteoric iron, as well as olivine and sulfides. The meteor was picked up by the Russian satellite Meteosat-9.
Next the students examined a fragment originating from the meteorite explosion that took place 37 kilometers above the Nubian Desert in Sudan on October 7th, 2008. The meteor entered Earth's atmosphere above northern Sudan at 02:46 UTC (05:46 local time) with a velocity of 12.8 km/s at an azimuth of 281 degrees and an altitude angle of 19 degrees to the local horizon. It exploded tens of kilometers above the ground with the energy of 0.9 to 2.1 kilotons of TNT over a remote area of the Nubian Desert causing a large fireball or bolide, with an estimated total mass of 80 tonnes. From that some 600 meteorites, weighing a total of 10.5 kilograms, were recovered; many of these belonged to a rare type known as ureilites which contain, among other minerals, nanodiamonds. It was the first time that an asteroid impact had been predicted prior to its entry into the atmosphere as a meteor. The explosion was picked up by the weather Meteosat-8 satellite. Moreover, the students examined minute quantities of Moon and Mars dust powder obtained for Moon and Mars meteorite fragments ejected from the surface of Mars and Moon respectively.
Finally, Dr. Ioannis Haranas the course instructor presented to the class the surprise of the semester, an approximately 90 kg meteorite found in the Sahara desert of Morocco. This is an L-6 type chondrite. Chondrites are the second most common category of meteorites, accounting for approximately 35% of all those catalogued and 40% of the ordinary chondrites. Their mineral composition is olivine and hypersthene, as well as iron-nickel and troilite. Petrologic type 6 dominate, with over 60% of the L chondrites falling into this class. This indicates that the parent body was sizeable enough, greater than 100 kilometres in diameter to experience strong heating.
The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the chondrite, L chondrite and LL chondrite groups respectively. The parent body/bodies for this group are not known, but plausible suggestions include 433 Eros and 8 Flora, or the Flora family as a whole. 433 Eros has been found to have a similar spectrum, while several pieces of circumstantial evidence for the Flora family exist: (1) the Flora family is thought to have formed about 1,000 to 500 million years ago; (2) the Flora family lies in a region of the asteroid belt that contributes strongly to the meteorite flux at Earth; (3) the Flora family consists of S-type asteroids, whose composition is similar to that of chondrite meteorites; and (4) the Flora family parent body was over 100 kilometres in diameter. The possible age of this meteorite on the Earth is anywhere 500-1000 years, which implies that the meteorite fell in the Sahara desert 500-1000 years ago, where its own age of origin is much older than that in the range of half a billion to a billion years!! Students were not only impressed but also excited because they had an opportunity to see and touch an old solar system body which landed on the Earth such a long time ago. Some of them described it as an one life time experience and they wished we had more of these taking place in science courses!
Closing we say that the meteorite will remain at the physics and computer science department for few months where students, faculty and public can come and examine it at close range.