The (not as) unexpected absence of amino acids in heated CI chondrites

Ivuna meteorite

Amino acids are used in biology to make proteins. As such, they are essential for life as we know it. Amino acids of abiotic origin have also been found in meteorites, including seven of the eight different groups of carbonaceous chondrites, a subset of meteorites that contain up to 5 weight-percent carbon. Thus, the general assumption when carbonaceous chondrites are analyzed, then, is that indigenous amino acids will be found. Through the analysis of amino acid abundances and distribution in meteorites, our understanding of how these compounds could have been formed and how likely they are to be found throughout the solar system has been greatly improved.

Because amino acids are so widespread among carbonaceous chondrites, it is important to understand the range of conditions that allow amino acid synthesis to occur, and what conditions are inhospitable to these molecules, either by preventing their formation to begin with or leading to their rapid destruction. One way of identifying conditions that are favorable or disfavorable for amino acid formation and survival is to compare the amino acid distributions of meteorites that are chemically similar but experienced different parent body conditions (e.g., more or less heating, water activity, etc.).

A previous blog post on this subject discussed samples of the Sutter’s Mill meteorite, a CM2 chondrite that fell in Caloma, California in 2012. Because most CM2 chondrites contain indigenous amino acids, the Sutter’s Mill stones were expected to contain amino acids as well. This expectation was not borne out, however. Unlike most CM2 chondrites that experienced relatively low temperature aqueous alteration, the Sutter’s Mill meteorites had been heated to temperatures of 400 °C and above, in some cases. These observations, coupled with laboratory experiments by others that showed rapid degradation of amino acids in water at temperatures above 150 °C, led to the hypothesis that elevated parent body temperatures are not hospitable for amino acids.

We (Aaron Burton, NASA JSC, along with researchers from the NASA Goddard Space Flight Center and River Hill High School) observed a similar absence of amino acids in CI chondrites that had experienced parent body heating. More typical CI chondrites such as Orgueil and Ivuna experienced parent body temperatures 150 °C, and contain appreciable levels of amino acids. The meteorites analyzed in this study, Yamato 86029 and Yamato 980115 experienced temperatures of up to 600 °C in addition to the aqueous alteration that is ubiquitous in CI chondrites. Again, there is a correlation between heating and an absence of amino acids as we observed with the Sutter’s Mill meteorites, supporting the hypothesis that the combination of parent body heating and water activity either prevents the formation or leads to the destruction of amino acids in meteorite parent bodies.

These findings help us to place limits on the stability of amino acids, and inform us about whether or not we should expect to find amino acids and potentially other molecules of biological importance, on various planetary bodies in space.

Stardust Team Reports Discovery of First Potential Interstellar Space Particles

Michael Zolensky & Stardust aerogel collector
Michael Zolensky & Stardust aerogel collector

The largest interstellar dust track found in the Stardust aerogel collectors was this 35 micron-long hole produced by a 3 picogram mote that was probably traveling so fast that it vaporized upon impact. The other two likely interstellar dust grains were traveling more slowly and remained intact after a soft landing in the aerogel.
Image Credit: Andrew Westphal, UC Berkeley

Seven rare, microscopic interstellar dust particles that date to the beginnings of the solar system are among the samples collected by scientists who have been studying the payload from NASA’s Stardust spacecraft since its return to Earth in 2006. If confirmed, these particles would be the first samples of contemporary interstellar dust.

A team of scientists has been combing through the spacecraft’s aerogel and aluminum foil dust collectors since Stardust returned in 2006.The seven particles probably came from outside our solar system, perhaps created in a supernova explosion millions of years ago and altered by exposure to the extreme space environment.

The research report appears in the Aug. 15 issue of the journal Science. Twelve other papers about the particles will appear next week in the journal Meteoritics & Planetary Science.

“These are the most challenging objects we will ever have in the lab for study, and it is a triumph that we have made as much progress in their analysis as we have,” said Michael Zolensky, curator of the Stardust laboratory at NASA’s Johnson Space Center in Houston and coauthor of the Science paper.

Stardust was launched in 1999 and returned to Earth on Jan. 15, 2006, at the Utah Test and Training Range, 80 miles west of Salt Lake City. The Stardust Sample Return Canister was transported to a curatorial facility at Johnson where the Stardust collectors remain preserved and protected for scientific study.

Inside the canister, a tennis racket-like sample collector tray captured the particles in silica aerogel as the spacecraft flew within 149 miles of a comet in January 2004. An opposite side of the tray holds interstellar dust particles captured by the spacecraft during its seven-year, three-billion-mile journey.

Scientists caution that additional tests must be done before they can say definitively that these are pieces of debris from interstellar space. But if they are, the particles could help explain the origin and evolution of interstellar dust.

The particles are much more diverse in terms of chemical composition and structure than scientists expected. The smaller particles differ greatly from the larger ones and appear to have varying histories. Many of the larger particles have been described as having a fluffy structure, similar to a snowflake.

Read More in “Stardust Team Reports Discovery of First Potential Interstellar Space Particles“,  NASA Press Release 14-219 (Aug 14, 2014).