Perhaps you have contemplated the existence of life on other planets or considered the enormity of how life as we know it evolved. Certainly, scientists from disciplines from biology to astronomy have considered these questions, and they have new details to share based on the analysis of a fragment of the asteroid Bennu. This sample, about ten times the size of previous samples from other asteroids, was retrieved from Bennu by a robotic spacecraft launched by NASA. Unlike meteorites which crash to the Earth’s surface and become contaminated by our atmosphere, this sample was carried back to Earth and analyzed in a sterile environment to decipher the contents that were truly native to the asteroid. 

One key finding was that the asteroid contained all 5 nucleobases that make up DNA and RNA and 14 of the 20 amino acids that make up proteins, which are essential building blocks of Earth life. This evidence supports the theory that life on Earth was seeded by similar asteroids. However, one mystery about the symmetry of the amino acids remains unsolved. While Earth life generally uses only left-handed amino acids, asteroid Bennu contained about equal amounts of left- and right-handed amino acids. This means that life on Earth evolved to use only one version of these molecules, and the answer to why is not clear from the contents of the asteroid. Another discovery was the presence of salts and carbon-rich molecules, indicating that the celestial body where Bennu came from likely contained a water source that dried up to leave behind these minerals. Evidence for liquid water and organic chemistry on such bodies suggests that the precursors for life, such as water, salts, and complex carbon molecules, may have been delivered to Earth on asteroids like Bennu.

The analysis of this sample is both fascinating and perplexing. It supports the idea that the building blocks of life as we know it are not unique to Earth and that we evolved to use only some of the available types of molecules. Scientists from the astronomy community support more missions to retrieve these types of key samples, or even to look for planets that could be the origins of asteroids with clues to life.

This study was led by Daniel P. Glavin and Jason P. Dworkin in the Solar System Exploration Division at NASA.

Managing Correspondent: Olivia Lavidor

Press Article: Asteroid fragments upend theory of how life on Earth bloomed (Nature Briefing) 

Original Journal Articles: Abundant ammonia and nitrogen-rich soluble organic matter in samples from asteroid (101955) Bennu (Nature Astronomy)

Image Credit: CharlVera/pixabay