Exploring Terrestrial Meteorites

Julie Levine
Posted on Jul 29, 2018

The following blog post accompanies this interactive web application, exploring data on terrestrial meteorites.

Introduction

Although most of us may never have the opportunity to leave the bounds of Earth, we can still explore materials which originated from outer space. I’m talking about meteorites. Meteorites are essentially space stuff— bits of debris from celestial objects, like comets and asteroids (even pieces of other planets and moons), which have survived the trip through space all the way to the surface of a new planet or moon. The NASA Open Data Portal provides a dataset with detailed information on over 30,000 terrestrial meteorites, sourced from the Meteoritical Society. You can explore this data yourself with this interactive web application:

https://lejulie.shinyapps.io/meteorite_app/

This app was built using R Shiny. You can check out the codebase on github.

Meteorite metrics

Meteorites vary greatly in size, shape, and composition, as well as in where, when, and how they are found. This dataset provides information on:

  • Mass
  • Classification
  • Date recorded
  • Find or fall (whether someone observed the meteorite falling to Earth or it was later identified as a meteorite by its properties)
  • Find/fall location

Mapping meteorites

Meteorites can come from a variety of celestial sources, and can land anywhere around the globe. However, there are some interesting trends in where meteorites are recorded. For starters, check out the map below:

Map of terrestrial meteorites

A few things jump out:

There are are no meteorites in the oceans

Perhaps the most obvious feature of this graph, that there are no meteorites recorded in the oceans, also has an obvious answer: once a meteorite lands in the ocean, it will quickly be lost to the depths where it is unlikely to ever be found by a human and recorded.

There are far more “found” meteorites than “fell” ones

Of the approximately 32,000 meteorites mapped in this dataset, nearly 31,000 are found. There are a few factors at play here. In order for a meteorite to be categorized as fell:

  • a human must observe it falling
  • it must survive the fall and impact with the earth
  • it must be tracked down and then recorded

However, a found meteorite need only survive the fall to earth and then lie undisturbed until it is discovered, deduced to be a meteorite, and recorded. The latter is far more likely.

A closer look at the numbers: meteorites by country

Rank Country Count Fell Count Found Total Count Percent of All Meteorites Running Total
1 Antarctica 0 11,918 11,918 37% 37%
2 South Africa 17 6,426 6,443 20% 58%
3 Oman 0 2,996 2,996 9% 67%
4 French Southern Territories 0 2,494 2,494 8% 75%
5 United States 146 1,504 1,650 5% 80%
6 Libya 1 1,487 1,488 5% 85%
7 Argentina 20 957 977 3% 88%
8 Australia 17 622 639 2% 90%
9 Algeria 7 615 622 2% 92%
10 Chile 1 518 519 2% 93%

Where to hunt for meteorites

One of the key factors for determining a successful meteorite hunting-ground is climate: arid climates are the best for preserving meteorites after they land. The longer a meteorite is preserved, the greater the likelihood is of it being discovered. It’s thus no surprise that countries like Antarctica, the French Southern Territories, and Oman rank at the top of list. However, the numbers in countries such as South Africa, Argentina, and Chile are less expected. Upon further inspection, we see that the majority of meteorites recorded for these countries were actually found in regions of Antarctica that they have laid claim to. For example, see the meteorites assigned to Argentina below:

Meteorites recorded in Argentina

*Note: Countries were derived using this reverse geocoder, provided by Ajay Thampi.

Why Antarctica?

If we treat all meteorites on the Antarctic continent as “Country: Antarctica” we see that this covers closer to 70% of the total dataset. In addition to climate, there are a few other reasons why so many meteorites are discovered there. For one, meteorites tend to be dark in color, which causes them to stand out against the snow white surfaces in Antarctica. Perhaps more importantly, most of the surface of Antarctica is made up of ice sheets that can regularly melt to reveal meteorites long since buried.

Meteorite mass

In addition to location, we can also explore the distribution of masses amongst meteorites. When we plot these in a histogram, we see that the vast majority of meteorites are quite small (under 200g). One possible reason for this is that the process of traveling through Earth’s considerable atmosphere takes a serious toll. Most meteors (objects in the process of falling to Earth) never make it all the way to the surface but are instead completely “burned up” or blown apart. Those that do survive may languish on the ground for many years before being discovered (recall that most meteorites are found), during which time they can erode significantly.

Histogram of meteorite masses

Meteorite milestones

Next, we examine how many meteorites have been found over time. When we plot meteorite records by year, it’s clear that the vast majority of meteorites were recorded in the past two centuries. It’s reasonable that over time methods for discerning meteorites, as well as keeping standardized records, would improve.

Histogram of years meteorites were recorded

If we dig a little deeper, we see that the number of meteorites recorded per years begins to rise significantly in the late 1970s.

Meteorites recorded in the 1900's and on

When we narrow the scope of the histogram to only meteorites found in Antarctica, we see that they account for a large portion of this trend.

Timeline of meteorites recorded in Antarctica

Another notable uptick in meteorite discoveries is visible in Oman, where the pursuit of meteorites in the desert has grown in popularity since the late 1990s.

Timeline of meteorites recorded in Oman

Top class

Meteorites are classified according to their physical and chemical properties. The most common classes of meteorites by count are detailed below.

Rank Class Count Fell Count Found Total Count Percent of All Meteorites Running Total
1 L6 255 6,268 6,523 20% 20%
2 H5 159 5,427 5,586 17% 38%
3 H4 50 3,274 3,324 10% 48%
4 H6 91 3,140 3,231 10% 58%
5 L5 76 2,647 2,723 9% 67%
6 LL5 19 1,878 1,897 6% 73%
7 LL6 41 922 963 3% 76%
8 L4 18 781 799 3% 78%
9 H4/5 6 374 380 1% 80%
10 CM2 15 264 279 1% 81%

The L and H group meteorites above, which account for 80% of all meteorites, are both subclasses of chondrites. The similar compositions of chondrite meteorites provide valuable insight into what materials are common in our solar system. Learn more about meteorite classification here.

Learn more

To learn more about meteorites, explore the app here. To get a look at the underlying code, check out the repository on github.

About Author

Julie Levine

Julie Levine

Julie Levine has a BSE in Chemical and Biomolecular Engineering from The University of Pennsylvania. She has worked in a variety of roles in marketing and product management at tech companies including Factual and Datadog. Currently, she is...
View all posts by Julie Levine >

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