In space, there are clouds that contain gas and dust from stars. Our solar system formed 4.6 billion years ago from a molecular cloud. Most dust grains were destroyed during this formation. The dark areas in the Carina Nebula image are molecular clouds. However, a small amount of grains survived and remained intact in primitive meteorites, known as presolar grains because they predate the solar system. Scientists study these grains to understand the early solar system and beyond.
Presolar grains like the one in the image existed billions of years ago in molecular clouds before reaching Earth in meteorites. The image shows a grain of silicon carbide (SiC) taken by a scanning electron microscope. This grain was extracted from the Murchison meteorite that fell in Australia in 1969. Scientists analyze the physical properties of these grains to determine their origin. For example, the ratio of stable isotopes ¹²C and ¹³C in carbon can reveal whether the grain originated within the solar system or in a star.
If a grain originated within the solar system, its ¹²C/¹³C ratio would be 89. The grain in the image has a ratio of about 55.1, indicating its stellar origin. This particular grain formed in a type of star called an asymptotic giant branch star, which produced and expelled dust into space over 4.6 billion years ago. Other types of presolar grains found in meteorites include diamond, graphite, oxides, and silicates. Studying these grains helps researchers understand nucleosynthesis in stars, mixing of different zones in stars, and how abundances of elements and isotopes change over time in the galaxy.
Sachiko Amari, a Research Professor of Physics, Arts & Sciences at Washington University in St. Louis, explores the origins of presolar grains and their significance in understanding the universe. This research provides valuable insights into the processes that shaped our solar system and the elements that make up our world. By studying these ancient stardust particles, scientists can unravel the mysteries of space dust origins and the evolution of stars. The discovery of presolar grains on Earth opens a window into the cosmic past, offering a fascinating glimpse into the origins of our existence and the vast universe beyond.
