Meteorite expert Mike Reynolds chats about falling stars

While chatting with Astronomy magazine Contributing Editor Mike Reynolds the other day, he proposed a (roughly) monthly series that focuses on meteorites. Everyone here loved the idea, so it’s my job to introduce Mike and the first of the series. No problem.

Reynolds has spent 34 years in astronomy and space sciences in the gamut of a high school and university instructor, planetarium and museum director, researcher, writer, and lecturer. He earned his Ph.D. in Astronomy and Science Education from the University of Florida. Reynolds has received widespread recognition for his work, including his selections as the 1986 Florida State Teacher of the Year, NASA Teacher-in-Space National Finalist, and the G. Bruce Blair Medal winner.

He has written a number of astronomy books, including the book Falling Stars (about meteorites) and articles. Reynolds has led numerous astronomical expeditions worldwide and has also served as an invited speaker internationally. Mike is Executive Director Emeritus of the Chabot Space & Science Center in Oakland, California, and is currently Dean of Liberal Arts and Sciences and teaches astronomy at Florida State College in Jacksonville.

Falling Stars!

Welcome to Astronomy magazine’s latest blog about meteorites. We will explore different meteorite falls and finds, types of meteorites, meteorite shows, and the latest in this monthly blog. And if somebody recovers a new meteorite, I’ll immediately blog about the new find.

I got my start in meteorites as a third-grader when my class went to a children’s museum. I was already interested in astronomy and space, so while visiting the museum’s gift shop I was looking for anything astronomical. What caught my eye was a small Canyon Diablo meteorite; I spent my milk money and the 50 cents my parents had given me to buy something at the museum’s gift shop on this meteorite. That started a passion for these fascinating rocks from space. And yes, I still have that meteorite!

Canyon Diablo is an iron meteorite; one of three major classes or groups of meteorites based on their compositions. And meteoriticists further divide each class based on specific characteristics.

• Iron Meteorites – composed primarily of iron and nickel, accounting for about 5 percent of all meteorite falls. Scientists further classify these dense objects based on the iron-to-nickel ratio. When sliced and then etched with acid, some irons produce spectacular patterns of lines due to iron-nickel matrix crystalline arrangement. Earth irons do not exhibit this pattern.
• Stone Meteorites – contain about 75 percent to 90 percent silicate materials; they account for more than 94 percent of falls. Most stony meteorites contain iron-nickel alloy. Stones fall into classifications based on the inclusion or lack of chondrules (millimeter-sized spherical crystals). Stony meteorites include the rare lunar and martian meteorites whose origins can be traced back to the Moon or Mars.
• Stony-Iron Meteorites – a mixture of silicates and iron-nickel in roughly equal proportions; only about 1 percent of all falls. Stony-irons divide into two groups based on how the mixture distributes. Pallasites, one class of stony-irons, are perhaps among the most spectacular meteorites when sliced and collectors treasure them for their beauty.

People usually think of iron meteorites as the predominant type; they are not. Iron meteorites, often called “irons,” make up only a small percentage of all meteorite falls. Irons look and feel like what a meteorite “should,” thus the misconception that they are the classic meteorite type. We’ll explore all three types of meteorites throughout these blogs. And by the way – stony meteorites — or “stones” — make up the greatest number of recovered meteorite falls and finds. (A fall occurs when someone sees a meteor and recovers a meteorite or meteorites. A find happens when somebody simply finds a meteorite with no known associated fall.)

How easy or hard is it to find a meteorite? According to one source, there is more total gold worldwide — 2,000 tons or so — than the total mass of all meteorites recovered in the world in museum, university, and private collections. Scientists estimate that between 20,000 and 100,000 tons of material enter Earth’s atmosphere each year; however, most of it:

• Burns up in Earth’s atmosphere;
• Becomes atmospheric dust;
• Lands in the ocean; or
• Is simply never found.

Think about the water-to-landmass ratio of Earth (Arthur C. Clark said it best when he stated, “How inappropriate to call this planet Earth when clearly it is Ocean…”). And consider the amount of land that is simply inaccessible. Yet people recover new meteorites all the time, some from fresh falls.

Meteoriticists estimate that more than 45 tons of meteoritic material has come from the famous Canyon Diablo meteorite fall of approximately 25,000 to 50,000 years ago. Canyon Diablo meteorites classify as iron — coarse octahedrite (IAB).

One of my favorite meteorites in my collection: a 994-gram Canyon Diablo iron meteorite that was “pinched” at one end during the final impact of that massive fall. Mike Reynolds Photo

Canyon Diablo meteorites are wonderful iron meteorites, often displaying the incredible forces of impact. Samples have also been known to contain diamonds or other interesting inclusions. Cut, polished, and etched Canyon Diablo specimens demonstrate the Widmanstätten pattern, due to nickel-rich and nickel-poor bands within the crystals. In 1808, Count Alois von Beckh Widmanstätten, a Viennese scientist, independently discovered patterns in iron meteorites. Even though the pattern carries Widmanstätten’s name, English geologist G. Thompson first noted it and published his results in the French Bibliothèque Britannique in 1804. The patterns represent a section through the three-dimensional octahedral structure in the iron meteorite formed of bands of kamacite with narrower borders of taenite. Only iron meteorites exhibit these patterns.

Someone machined this Gibeon, an iron — fine octahedrite (IVA) meteorite, into a cue-ball sized sphere. They then etched it with acid to show the Widmanstätten pattern. Mike Reynolds Photo

The Canyon Diablo crater, known as Barringer Crater or Meteor Crater, is one of the youngest “large” craters on Earth. Apollo astronauts used Meteor Crater for training prior to their lunar surface missions. If you are ever near Flagstaff or Winslow, Arizona, in Coconino County, Meteor Crater is a must-see stop. The designers of the U.S. Interstate System did us a great favor in building Interstate 40 just north of Meteor Crater.

Please note that it is illegal to hunt for meteorites at the Barringer Crater. In fact, you should always have permission to hunt for meteorites when on private property; the laws in the United States are specific in this regard. Laws vary from country to country; some do not allow the export of meteorites whatsoever. We will explore these legalities more fully in future blogs.
Do you have a meteorite or cratering question? How – and where – to buy meteorites? Collecting tales? Successful meteorite hunts? A favorite meteorite? Favorite meteorite books and publications? A must-see meteorite exhibit? Please e-mail me at my college address: mreynold@fscj.edu. We will explore your meteorites questions and more each month!

Keep looking up!
Dr. Mike Reynolds

Related video:

Collecting meteorites, with Editor David J. Eicher (available to magazine subscribers)