Collection and observation
Have you ever seen the Falling Star? Have you been curious, where it lands? Have you ever intended to go to find it? Microscopic meteorites could be found in your backyard.
Meteoroid – It is a small piece of rock, ice or even metal moving through universe. They range in size from a speck of dust to one meter.
Meteor – It is the meteoroid that has entered the atmosphere of the Earth. During its burning in atmosphere appears as bright spot with a flaming tail and/or a smoke. More commonly 'The Shooting Star' or 'The Falling Star' is called. Most meteors burn up completely in the atmosphere.
Meteorite – It is a fragment of meteoroid that survived entry through the atmosphere and reached the surface of the Earth. It happens very rarely. Most of meteorites are based on stone, but moreover some of them are also metallic form. These usually contain iron in a bulk with additional of another metallic elements as are nickel, cobalt and so on.
Micrometeorites are small meteorite that usually have very low mass and therefore they do not get burned along their way through atmosphere. Some of them could be created as small fragments from the large meteor during its disintegration. These very small particles can be in dust form in the atmosphere. They slowly move towards the surface of the Earth or are accelerated by rain. Their size is usually in order of tenths of micrometer. At times also the 'big' micrometeorites in range from 1 to 2 mm are appeared.
On the basis what has been said above, micrometeorites falling freely on surface of the Earth with dust which is situated in the atmosphere. Settled dust from large area is necessary to picked up. The collector should realise that dust should not be contaminated by impurities from the ground. That could be accomplished by capturing of rainwater direct from roof. Even better option is using the top layer of snow and let it melt. The snow could collect the meteorites for a long period of several months. As melted water or rainwater collected in a big plastic container let stand for several days. During that time, the dust containing the meteorites falls to the bottom of the container. The best time to do the collection is after meteor showers. It is periodic event when the Earth passes a space region with high concentration of meteoroids. Though, random meteors are reaching the Earth during the whole year. At the beginning is better to focus on meteorites of metallic form, since they are magnetic and it is easy to separate them from non-magnetic tailings. The magnetic particles could be pulled out from the canister by the magnet placed in plastic bag. After that follows overturn of bag thus the particles are separated from the magnet.
Translation of particles on clock glass for further observation could be carried out by magnetized steel needle. The Magnet could be used for magnetized of needle. Some spherical particles could not be the micrometeorites. Instead of are concerned to be ash, remains of powder metallurgy or condensed combustion gas from chimneys. However, detailed chemical analysis is desired to do that confirmation.
Collected particles rinsed out in alcohol, dried on the air and subsequently observed under microscope. Spherical particles with regular shape and glossy surface are supposed to be the micrometeorites.
Quite 'big' micrometeorite.
The basic observation is usually carried out on surface of the micrometeorites. On the other hand, the cross section observation could be much more interesting. The samples for cross section were prepared as follows. The micrometeorites were placed on the bottom of a small plastic canister. The small drop of epoxy resin was added very carefully and it was repeated several times every time after encapsulation of epoxy resin. The micrometeorites were encapsulated on the bottom side. Grinding was carried out on very smooth grinding papers and was applied very low load force. The grinding was controlled by microscope and it was stopped at the time of appearing of inner surface of micrometeorites. Samples were polished with diamond suspension up to a mirror finish. The last step consisted in dipping the samples in etchant of 5% of nitric acid for several second. Topography for observation was created by different reactivity between structural components of micrometeorites and nitric acid.
Detail of dendritic microstructure typically for metal alloy.
Scanning electron microscopy
Light microscope could be simply used for observation of micrometeorites and their cross section. Unfortunately, the spherical surface is out of the depth of field at high magnification. Therefore, the scanning electron microscopy is much more useful for conductive metals samples. Electron beam is used for observation and much better resolution and much higher depth of field are obtained at a big magnification. Microstructure of different micrometeorites from electron microscopy documented following pictures. Click for enllarge.
Article is aviable in online magazine MicrobeHunter 5/2014