Amino Acids in Antarctic

A team of astrobiologists from NASA’s Goddard Space Flight Center and the Carnegie Institution for Science has found a wide diversity of amino acids in Asuka 12236, a carbonaceous chondrite meteorite recovered from the Nansen Ice Field in Antarctica by Belgium and Japan researchers in 2012.

This SEM image shows a polished thin section of Asuka 12236. The section is about 1 cm (a third of an inch) across. Most of the bright grains in the image are iron-nickel-metal and/or iron-sulfide. The gray is mostly silicate, with the darker gray areas more magnesium-rich, while the lighter gray areas are more iron-rich. The roundish objects, and some fragments of them, that tend to contain most of the small, bright metal grains are called chondrules, which formed as molten droplets. They are set in a very fine-grained matrix, which is where the organic compounds and presolar grains are found. Image credit: Carnegie Institution for Science / Conel M. O’D. Alexander.

Lead author Dr. Daniel Glavin of NASA’s Goddard Space Flight Center and colleagues analyzed Asuka 12236 and found various amino acids, such as glycine, alanine, serine, α-aminoisobutyric acid, isovaline, aspartic and glutamic acids, inside it.

Several lines of evidence suggest that the original chemical makeup of this space rock is the best preserved in a category of carbon-rich meteorites known as CM chondrites.

The interior of this meteorite is so well-preserved because it was exposed to very little liquid water or heat, both when it was still a part of an asteroid and later, when it sat in Antarctica waiting to be discovered.

“It’s fun to think about how these things fall to Earth and happen to be full of all this different information about how the Solar System formed, what it formed from, and how the elements built up in the galaxy,” said co-author Dr. Conel Alexander, a researcher at the Carnegie Institution for Science.

The scientists are learning that the key for amino acids, when it comes to forming and multiplying, is exposure to the perfect conditions inside asteroids.

“You need some liquid water and heat to produce a variety of amino acids. But if you have too much, you can destroy them all,” Dr. Glavin said.

The water would have been produced inside the asteroid that Asuka 12236 came from, as heat from the radioactive decay of certain chemical elements melted the ice that condensed with rock when the asteroid first formed.

Given that Asuka 12236 is so well-preserved, it could have come from a cooler outer layer of the asteroid where it would have come in contact with little heat, and thus, water.

“Though that’s just conjecture for now. There’s still a lot we don’t know about this meteorite,” Dr. Glavin said.

The study authors also found that Asuka 12236 had more left-handed versions of some amino acids.

“There’s a right-handed and left-handed mirror-image version of each amino acid. All known life uses only left-handed amino acids to build proteins,” they said.

“The meteorites are telling us that there was an inherent bias toward left-handed amino acids before life even started. The big mystery is why?”

The left-handed molecules would have needed to be processed in a lot more water than Asuka 12236 seems to have been exposed to.

“It is pretty unusual to have these large left-handed excesses in primitive meteorites,” Dr. Glavin said.

“How they formed is a mystery. That’s why it’s good to look at a variety of meteorites, so we can build a timeline of how these organics evolve over time and the different alteration scenarios.”

“Understanding the kinds of molecules, and their handedness, that were present in the earliest days of the Solar System puts us closer to knowing how the planets and life formed,” said co-author Dr. Jason P. Dworkin, an astrobiologist at NASA’s Goddard Space Flight Center.

The findings were published in the journal Meteoritics and Planetary Science.

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Daniel P. Glavin et al. Abundant extraterrestrial amino acids in the primitive CM carbonaceous chondrite Asuka 12236. Meteoritics and Planetary Science, published online August 20, 2020; doi: 10.1111/maps.13560