Micrometeorites are tiny particles from space that have landed on the surface of the Earth. No larger than a grain of sand, most micrometeorites come from comets and asteroids. Some, however, may travel to us from the outermost reaches of our solar system and beyond. Put simply, they are the oldest matter there is and nothing on Earth has traveled farther.
Shortly after I discovered the world’s first urban micrometeorite in 2015, I began engaging with fellow micrometeorite enthusiasts from around the world on social media. I received many questions about how to find micrometeorites and many others about how micrometeorites can be classified. What do the different types look like? What are they made of? And, how are they formed?
The first two of these questions have been explored quite thoroughly by myself and several of my academic colleagues. This latter question, however, remains somewhat of an enigma. In fact, Jan Braly Kihle and I recently began a new research project with Dr. Roar Skartlien from the Institute for Energy Technology (IFE) to investigate this very question.
Because this is such a popular question, I thought it would be fun (and helpful) to summarize what is currently known about each of the different micrometeorite types here on the Project Stardust blog. My hope is that this blog series will be interesting to refer back to as our new research project continues and our understanding of micrometeorite formation changes over time.
When cosmic dust particles end their journey, their path through our atmosphere transforms them from rough space minerals into polished jewels. Depending on the angle of entry, initial mass and speed, heat caused by friction will vary significantly. This in turn leads to substantial differentiation in both chemical and morphological characteristics.
To begin this series, I will first introduce barred olivine micrometeorites. Enjoy!
Barred Olivine (BO-type) Micrometeorites
When one first begins hunting for stardust, it is overwhelmingly likely that the first micrometeorite to be encountered will be a barred olivine (BO-type), as this is the most common type. These cosmic particles are composed mainly of the magnesium variety of olivine, which is called forsterite, and have small amounts of magnetite in the interstitial glass.
Barred olivine particles melt completely as they descend through the atmosphere. While in a liquid state, surface tension bends the micrometeoroid into spherules, round particles, or subspherical aerodynamic stones.
Once the particle begins to cool during deceleration, magnetite and olivine crystals begin to form. Many BO-type particles are made of a single crystal domain, while others have numerous domains. The surface of barred olivine micrometeorites have striations that, with practice, become easily recognizable. At times, these striations will be punctuated by metallic magnetite “Christmas tree” crystals, which are formed when iron reacts with oxygen in the atmosphere.
Current estimates suggest that between 5-10% of barred olivine micrometeorites have at least one metal bead. These beads, if present, may serve as a nucleus for crystallization.
I hope you enjoyed learning about barred olivine micrometeorites! If you’re curious the micrometeorites in the featured image of this blog post are outlined below:
- Top row: NMM 2889 (Winter 2022 Collection), NMM 1, NMM 2172
- Middle row: NMM 930, NMM 4032, NMM 3193
- Bottom row: NMM 455, NMM 1380, NMM 4028
To learn more, check out our limited edition artbook, The Atlas of Micrometeorites, which includes dozens of astounding high resolution color images of every micrometeorite type in large format.
Give yourself the gift of a cosmic perspective. Our limited edition Winter 2022 Fine Art Collection includes barred olivine micrometeorite, NMM 2889, an aerodynamic ellipsoid particle with a captivating dark gray body color and fascinating circular crystal formations on its surface. To us, a gem like this serves as a potent reminder that no matter how bleak our surroundings may seem, we are always surrounded by beauty.