Asteroid Bennu reveals that life's building blocks may form in frozen, radioactive space
NASA's OSIRIS-REx mission returned pristine samples from asteroid Bennu, challenging the long-held belief that life's ingredients required warm liquid water to form. Instead, new isotopic analysis suggests these essential molecules may have emerged in harsh, frozen environments, expanding our understanding of how life's chemistry could arise across the solar system.
When NASA’s OSIRIS-REx spacecraft delivered material from asteroid Bennu to Earth in 2023, it provided scientists with a pristine time capsule from the dawn of the solar system. Among the findings were amino acids—the fundamental building blocks of proteins—and all five nucleobases necessary for DNA and RNA. These discoveries confirm that the raw materials for life were present in the early solar system, potentially delivered to planets like Earth by asteroids.
For decades, the prevailing theory for how these molecules formed was the Strecker synthesis, a process requiring warm, water-rich environments. However, isotopic analysis of Bennu’s glycine, the simplest amino acid, suggests a different origin. Researchers at Penn State found that Bennu’s chemistry differs significantly from the well-studied Murchison meteorite, which fell in 1969. The evidence indicates that Bennu's amino acids likely formed in frozen ice exposed to radiation in the outer solar system, rather than in the mild, liquid-water conditions previously assumed.
The samples also revealed a complex history of saltwater, with 11 minerals identified that typically form as briny water evaporates over thousands of years. This suggests an environment capable of fostering chemical interactions. Yet, the findings have introduced new mysteries. Amino acids exist in two mirror-image forms, and while life on Earth uses almost exclusively left-handed versions, Bennu contains an equal mixture of both. Furthermore, mirror-image versions of glutamic acid in the sample displayed unexplained differences in nitrogen signatures. These puzzles suggest that the pathways to life are far more diverse than once thought, leaving scientists with more questions about why life on Earth developed its specific chemical bias.
Source: NASA Science Live: Asteroid Bennu Originated from World with Ingredients and Conditions for Life
