We are Made of Starstuff

Notes from the Mini Museum: Extraterrestrial Amino Acids Specimen

"The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff."

Carl Sagan, Cosmos, 1980

Posted January 14th, 2020

Originally posted on July 26th, 2018. Updated with new information January 14th, 2019.

Each year nearly 40,000,000 kilograms (88.1 million pounds) of meteoritic material rains down on the Earth from outer space. Less than 1% of these falls holds traces of organic compounds, and within this tiny subset scientists sometimes come across even rarer material: amino acids.

The story of these extraterrestrial amino acids begins at 10:58 AM on September 28th, 1969. A bright fireball appeared in the sky near the small, riverside town of Murchison, Australia. Under tremendous stress, the bolide separated into three main pieces, spreading fragments across 13 square kilometers (5 sq.mi.), including one lump which crashed through a barn roof and landed in a pile of hay.

As astronomical as the odds might be for this soft landing, the Murchison meteorite would turn out to be literally one of the rarest of all meteorite finds: a remnant formed at the very birth of the solar system, which also happened to carry the building blocks of life.

The oldest of these meteorites, known as carbonaceous chondrites, date to the formation of the solar system. Recent studies suggest that the amino acids found in some carbonaceous chondrites may have come from the pre-solar nebula.

This type of meteorite is distinguished by calcium–aluminium-rich inclusions (CAI), minerals that are among the first solids to condense in the high temperature gases of a young, protoplanetary disk. In addition to CAIs, Murchison also carries a fantastic array of more than 70 different amino acids, including 8 of the 20 proteinogenic amino acids used to build proteins encoded in our DNA as well as all life here on Earth.

From This Day Tonight (1970): Murchison Meteorite (Australian Broadcasting Corporation)

Since the discovery of amino acids in the Murchison meteorite, scientists have discovered that other carbonaceous chondrites also contain amino acids. Recent studies suggest that the amino acids present in these meteorites may even pre-date the formation of the solar system. Further studies have revealed that the diversity of amino acids in a particular meteorite can be used to study the original parent or "host body" and how geological processes (including aqueous alteration) may have enriched these early organic chemicals prior to the emergence of life in this solar system.

If you are interested in learning more about this fascinating process I highly recommend reading this 2016 study, "Meteoritic amino acids: diversity in compositions reflects parent body histories." Led by Dr. Jamie Elsila (Cook), an astrochemist with NASA Goddard Space Flight Center’s Solar System Exploration Division, the study walks through the entire process and talks about other types of meteorites which also carry amino acids. Really incredible science!

Update January, 14th 2020: Even after decades of study, the Murchison meteorite continues to surprise science with new discoveries. The latest is that materials in this meteorite are likely far, far older than our own solar system. Billions of years older, in fact.

In "Lifetimes of interstellar dust from cosmic ray exposure ages of presolar silicon carbide", scientists at the Field Museum in Chicago, studied cosmic ray exposure of silicon carbide grains extracted from samples of the Murchison meteorite. In 12 samples, they discoverd strong evidence that these grains originated in stars formed roughly 7,000,000,000 years ago and were parts of aggregates travelling through the Interstellar Medium. Whether any of these particular grains are in a single specimen in the Fourth Edition is hard to say but it is incredible to think about!

"Interstellar dust is an important component of our galaxy. It influences star formation as well as the thermal and chemical evolution of the galaxy. Although dust only presents ∼1% of the mass in the interstellar medium (ISM), it carries a large fraction of the elements heavier than Helium, including the elements that form terrestrial planets and are essential for life. Thus, interstellar dust is a key ingredient of stars and habitable planetary systems, making increased knowledge about its composition and lifecycle desirable."

Creating the Specimen

The specimen in the Mini Museum is composed of two special carbonaceous chondrites: Murchison and Jbilet Winselwan. Both of these meteorites are CM2 class carbonaceous chondrites, a class known to contain the highest density of amino acids.

Extraterrestrial Amino Acids - CM2 Carbonaceous Chondrites

The source material is cleaned and then carefully reduced by hand using a steel mortar and pestle.

Preparing the Specimen for Reduction

Once we have prepared various densities of material, we begin making small test sheets. The process of making a sheet is slow but very satisfying. As you can see in this short video clip, multiple passes are made over every section.

After finishing the test sheets, they’re allowed to cure. The image below shows the very first test sheets for this specimen, which Grant then turned into finished specimens for review.

Completed Test Sheets of Extraterrestrial Amino Acids

Once we have confirmation that our process is solid, we produce full sheets like the one below.

Production Sheet of Extraterrestrial Amino Acids

Here’s a short video of Grant removing a cured production sheet. Sometimes they stick a little but they are really quite durable.

The sheets are then carefully cut into slices using a guide like the one pictured below.

Cutting Guide and Slices

The completed slices for the production sheet Grant removed look a little like a jigsaw puzzle, albeit one with pieces that are 4,568,200,000 years old.

The slices are then turned into specimen sized pieces. Every piece is examined carefully to make sure that material is evenly dispersed throughout the specimen and that it will be visually appealing when encased in the Mini Museum.

Completed Specimens Ready for QA

There is nothing quite like working with some of the oldest matter in the solar system. I’m going to close out this post with a clip from Cosmos. It comes from Episode #9 “Stars - We Are Their Children.” I think it really encapsulates the entire feeling of this specimen so well.

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