There are many new stardust hunters out there, and some of you will find amazing space gems as soon as you’ve broken the code for identification. There are enough astounding micrometeorites and new discoveries in store for all of us.
In order to best help my fellow stardust hunters, there is one misconception I would like to erase: Micrometeorites are usually neither spherical nor metal. Instead, they are more typically aerodynamic particles made of magnesium silicates such as olivine, forsterite, and pyroxene. And, when metal is present, it typically appears in the form of a nickel-iron bead.
Introducing NMM 1453
Take, for example, this striking micrometeorite, which was recently re-photographed by yours truly and Jan Braly Kihle using our updated techniques. The beautiful NMM 1453 measures approximately 0.25 mm and is an elongated olive green glass or vitreous (V) type micrometeorite. The green color is due to a dominance of the iron cation, Fe2+. However, our favorite feature must be its large internal vesicles, which are clearly visible in its depths. In the front, which is up in the photo, an iron-rich metal mound has fallen off, possibly due to weathering. In addition, there is a smaller secondary nickel-rich metal bead at the rear end to the left. And finally, clearly visible in the scanning electron microscope (SEM) image, there is a third and even smaller metal bead in the center.
This remarkable particle most likely had a rapid spin during atmospheric entry that was perpendicular to the direction of movement. According to the Classification of Micrometeorites the stone has remained amorphous (glass) due to a very high peak temperature of nearly 2,000°C during atmospheric pulse heating.
Until just a few years ago, being able to deduce the complete formation process of a micrometeorite from its visual appearance was pure sci-fi! How extraordinary!