Penn State researchers think a key ingredient for life may have formed in deep freeze, not in a warm asteroid puddle.<\/p>\n
A space sample with a new twist<\/p>\n
Scientists at Penn State<\/a>; led by geoscientist Allison Baczynski and postdoctoral researcher Oph\u00e9lie McIntosh; studied amino acids in material from the asteroid Bennu. Their work appeared in the Proceedings of the National Academy of Sciences.<\/p>\n NASA\u2019s OSIRIS-REx mission delivered the Bennu sample to Earth in 2023. Earlier tests found amino acids in that 4.6-billion-year-old dust. Amino acids are the small molecules that join up to make proteins.<\/p>\n Analyzing a precious bit of space dust no bigger than a teaspoon, the Penn State team used custom instruments capable of measuring isotopes, slight variations in the mass of atoms. (CREDIT: Jaydyn Isiminger \/ Penn State) <\/p>\n The big question has been simple: Where did those amino acids form? Many scientists pictured mild, watery chemistry inside an asteroid. The Penn State team says Bennu\u2019s chemistry points somewhere colder.<\/p>\n \u201cOur results flip the script on how we have typically thought amino acids formed in asteroids,\u201d said Baczynski, an assistant research professor of geosciences at Penn State and co-lead author on the paper. \u201cIt now looks like there are many conditions where these building blocks of life<\/a> can form, not just when there\u2019s warm liquid water. Our analysis showed that there’s much more diversity in the pathways and conditions in which these amino acids can be formed.\u201d<\/p>\n Reading the \u201cfingerprints\u201d in atoms<\/p>\n The team worked with a speck of asteroid material, about a teaspoon in size. They measured isotopes; tiny mass differences in atoms that act like chemical fingerprints.<\/p>\n They focused first on glycine, the simplest amino acid. It has just two carbon atoms. Even so, it matters. Glycine is often treated as a sign that early \u201cpre-life\u201d chemistry was happening.<\/p>\n The researchers used highly sensitive tools to measure isotopes in extremely small amounts. They could detect molecules down to picomoles. Baczynski said the work depended on custom equipment at Penn State.<\/p>\n \u201cHere at Penn State, we have modified instrumentation that allows us to make isotopic measurements on really low abundances of organic compounds<\/a> like glycine,\u201d Baczynski said. \u201cWithout advances in technology and investment in specialized instrumentation, we would have never made this discovery.\u201d<\/p>\n Meteorite studies can be messy due to Earth contamination. Bennu\u2019s sample avoided much of that risk. It came straight from space; then stayed sealed and controlled.<\/p>\n The Penn State scientists involved in the study (from left to right) were Christopher House, professor of geosciences, and Katherine Freeman, Evan Pugh University Professor of Geosciences, Oph\u00e9lie McIntosh, postdoctoral researcher in Penn State\u2019s Department of Geosciences, Allison Baczynski, assistant research professor of geosciences, and Mila Matney (not picture), doctoral candidate in geosciences. (CREDIT: Jaydyn Isiminger \/ Penn State) Bennu vs. a famous meteorite<\/p>\n For decades, scientists have used carbon-rich meteorites as natural labs. One of the best known is the Murchison meteorite, which fell in Australia in 1969. Murchison holds many amino acids; and it has been studied for years.<\/p>\n The Penn State group compared Bennu\u2019s amino acids to Murchison\u2019s. The contrast was sharp.<\/p>\n \u201cOne of the reasons why amino acids are so important is because we think that they played a big role in how life started on Earth,\u201d said McIntosh, co-lead author and a postdoctoral researcher in Penn State\u2019s Department of Geosciences. \u201cWhat\u2019s a real surprise is that the amino acids in Bennu<\/a> show a much different isotopic pattern than those in Murchison, and these results suggest that Bennu and Murchison\u2019s parent bodies likely originated in chemically distinct regions of the solar system.\u201d<\/p>\n In Bennu, the team identified 19 amino acids in a powdered sample labeled OREX-800107-183. Several came in \u201cleft\u201d and \u201cright\u201d mirror forms. Many had carbon and nitrogen isotope values above typical Earth values. That supports a space origin.<\/p>\n Bennu\u2019s glycine showed a carbon isotope value of +21 \u00b1 6\u2030. Its nitrogen isotope value was +185 \u00b1 10\u2030. Bennu\u2019s \u03b2-alanine measured +12 \u00b1 6\u2030 for carbon; and +170 \u00b1 4\u2030 for nitrogen.<\/p>\n When the team compared carbon values to Murchison, they looked similar within uncertainty. Nitrogen was the standout. Murchison\u2019s glycine nitrogen value was +78 \u00b1 6\u2030. Murchison\u2019s \u03b2-alanine was +63 \u00b1 4\u2030. Bennu\u2019s were much higher.<\/p>\n Plots of \u03b415N (\u2030, Air) and \u03b413C (\u2030, VPDB) values for glycine and \u03b2-alanine obtained in this study for Bennu (OREX-800107-183; blue diamonds), compared with literature values for CM (gray squares), CR (gray hexagons), and CI (gray circles) chondrites. (CREDIT: PNAS) A colder way to make glycine<\/p>\n For years, a popular idea for making glycine in space rocks has been Strecker synthesis. In that pathway, hydrogen cyanide, ammonia, and an aldehyde or ketone<\/a> react in liquid water. It is a \u201cwet\u201d recipe.<\/p>\n Bennu\u2019s glycine did not match that story cleanly. The team measured glycine\u2019s two carbon positions separately. In Bennu, those two carbons looked similar within error. In Murchison, they looked very different.<\/p>\n They also measured certain aldehydes and ketones in another Bennu extract. Those compounds were more depleted in carbon-13 than Bennu\u2019s glycine. That mismatch made a Strecker-only explanation less likely for Bennu.<\/p>\n So the researchers pointed to another route: chemistry in ice exposed to radiation. In that picture, ultraviolet light or other radiation hits frozen ices. It creates reactive fragments. Later, those fragments can become amino acids.<\/p>\n Baczynski summarized it as amino acids forming \u201cin frozen ice exposed to radiation in the outer reaches of the early solar system<\/a>.\u201d The study says this kind of \u201cice photochemistry\u201d could make nitrile precursors. Those precursors could later turn into amino acids.<\/p>\n The team noted one caveat. Bennu\u2019s formaldehyde carbon isotope value has not been measured yet. If it turns out to be unusually enriched, Strecker chemistry could still play a role. More measurements are planned.<\/p>\n Allison Baczynski, assistant research professor of geosciences at Penn State, (left) led the study alongside Oph\u00e9lie McIntosh, postdoctoral researcher in Penn State\u2019s Department of Geosciences. (CREDIT: Jaydyn Isiminger \/ Penn State) A mirror-image mystery<\/p>\n