Cosmochemistry

Cosmochemistry, also known as chemical cosmology, is the study of the chemical composition of matter throughout the universe. Scientists in this field investigate the specific processes that led to these chemical compositions. They primarily achieve this by analyzing physical samples like meteorites. Because the asteroid parent bodies of meteorites were among the first solid materials to condense from the early solar nebula, they are vital clues. Most cosmochemical research focuses on objects within our own Solar System.

The history of this science began with the work of Victor Goldschmidt. In 1938, this Swiss mineralogist and his colleagues created a list of "cosmic abundances." This list showed the amounts of different elements found in space. Goldschmidt argued that studying only Earth rocks would be inaccurate. He believed terrestrial rocks undergo too much chemical change from Earth's internal processes and atmosphere. To get a robust and accurate picture of the cosmos, he concluded scientists must include extraterrestrial material. This idea formed the foundation of modern cosmochemistry.

As the field grew, new scientists expanded our understanding of the universe's history. Harold Urey is often called one of the fathers of cosmochemistry. His research helped explain the origin of elements and the abundance of chemicals in stars. In 1956, Urey and Hans Suess published a table of cosmic abundances that included isotopes. Isotopes are versions of elements that scientists identify through meteorite analysis. Later, in 1960, John Reynolds analyzed short-lived nuclides within meteorites. This work allowed him to determine that the elements of the Solar System formed before the Solar System itself. This helped establish a timeline for the early solar nebula.

Meteorites serve as the most important tools for these researchers. Many are as old as the Solar System itself, providing a direct record of the early solar nebula. Carbonaceous chondrites are a specific type of meteorite that are especially primitive. These rocks have retained their original chemical properties since they formed 4.56 billion years ago. Some of the most primitive meteorites even contain presolar grains. These tiny grains make up less than 0.1% of the meteorite's mass. They are older than the Solar System and come from the remnants of individual supernovae. These grains have exotic chemistries, such as matrices of diamond or silicon carbide, and isotope ratios that differ from our Sun.

Scientists also look to comets and interstellar dust to find chemical building blocks. In 2009, NASA identified the amino acid glycine in a comet for the first time. In 2015, the Philae lander touched the surface of comet 67/P. Its instruments revealed sixteen organic compounds, including acetone and methyl isocyanate. Researchers have also found complex molecules like polycyclic aromatic hydrocarbons, or PAHs, in space. These PAHs may be vital for the formation of early life. In fact, more than 20% of the carbon in the universe may be associated with PAHs. These molecules seem to have formed shortly after the Big Bang and are found near new stars.

Recent discoveries suggest that the ingredients for life might form in deep space. In 2012, astronomers found the sugar molecule glycolaldehyde around a star system 400 light years away. This molecule is necessary to form ribonucleic acid, also known as RNA. In 2013, the Atacama Large Millimeter Array confirmed finding two prebiotic molecules in an interstellar gas cloud. One molecule, cyanomethanimine, can produce adenine, which is a component of DNA. The other, ethanamine, may help form the amino acid alanine. These discoveries suggest that chemical sequences occur on the surfaces of ice grains in interstellar space. These molecules can then "seed" newly formed planets with the precursors for life.

This research connects the chemistry of the stars to the biology of Earth. NASA is currently using the Curiosity and Opportunity rovers to search Mars for evidence of ancient life. They are looking for organic carbon and signs of past environments that could have been habitable. By studying how molecules like DNA and RNA components form extraterrestrially, cosmochemists bridge the gap between space and life. They show how the dust from exploding stars eventually becomes the building blocks of living things.