Feb 14, 2025 06:00:00

Why do organisms on Earth only have 'left-handed' amino acids? What did we find out by analyzing the amino acids on the asteroid Bennu?

Amino acids , which are essential for biological molecules, have a structure in which functional groups such as amino groups, carboxy groups, hydrogen, and side chains are bonded to the carbon atom at the center of the molecule. Amino acids can be 'left-handed' or 'right-handed' depending on the arrangement of their chemical structures, but life on Earth has only left-handed amino acids in common. It is not exactly clear why 'only left-handed amino acids exist in life,' but an investigation of fragments of the near-Earth asteroid Bennu has revealed surprising results about left-handed amino acids that overturn previous predictions.

Abundant ammonia and nitrogen-rich soluble organic matter in samples from asteroid (101955) Bennu | Nature Astronomy
https://www.nature.com/articles/s41550-024-02472-9

NASA scientists want to solve a mystery: Why did life 'turn left?' | Mashable
https://mashable.com/article/nasa-bennu-asteroid-amino-acids-surprise

NASA: Mystery of Life's Handedness Deepens - NASA
https://www.nasa.gov/science-research/planetary-science/astrobiology/nasa-mystery-of-lifes-handedness-deepens/

The asteroid Bennu is a celestial body with an average diameter of about 560 meters that was discovered in 1999. It is said that it will approach Earth many times over the course of about 200 years, and in the worst case scenario, there is even a possibility of a collision. However, in addition to the risk of colliding with Earth, Bennu is also attracting attention as an celestial body from which valuable resources and research materials can be extracted.

10 reasons why we should use a space probe to investigate the asteroid 'Bennu' that may collide with Earth? - GIGAZINE

A paper published in January 2025 in the peer-reviewed scientific journal Nature Astronomy analyzed the organic molecules in samples from Bennu. Bennu is believed to be an object that has existed since the formation of the solar system, and identifying the organic compounds that make up Bennu is thought to help understand the processes that occurred during the formation and evolution of the early solar system.

The researchers boiled rocks and dust from Bennu in water and acid to extract organic compounds, then used mass spectrometry to identify the molecules, including 14 of the 20 amino acids that life uses to make proteins.

Previous research has reported that meteorites that have fallen to Earth contain about 1.6 times as many left-handed amino acids as right-handed amino acids, indicating that the proportion of left-handed amino acids is higher. Based on these research results, it was speculated that the reason that only left-handed amino acids are contained in life on Earth is because there are many left-handed amino acids in the solar system.

However, analysis of samples taken from Bennu revealed that left-handed and right-handed amino acids were almost equally mixed. Daniel Glavin, lead author of the paper, said, 'We studied Bennu to answer one of humanity's most persistent questions, but rather than supporting one of the leading hypotheses that the early solar system preferred left-handed amino acids and brought those components to the primitive Earth, this discovery overturned it. To be honest, I was a little disillusioned and disappointed. I felt like 20 years of research in our lab and my career had been wasted.' He spoke of the surprise of the discovery.

Glavin believes that previous research on meteorites may have been contaminated with proteins from Earth when they fell to the ground, making them not pure research samples. Jason Dworkin, project scientist for the OSIRIS-REx mission, which achieved the first sample return attempt in the United States, said that the reason why the analysis results of Bennu were different from previous meteorite research and prior speculations was, 'Bennu is a fragile type of asteroid that cannot maintain its shape after falling to Earth. That's why I think it hasn't been included in the research so far.'

According to the paper, Glavin and his team plan to further study the Bennu samples to investigate whether more amino acid samples are right-handed or left-handed. 'If we find that there is a strong bias towards either left-handed or right-handed, we can think that there may be something biological behind it,' Glavin said. 'If that's the case, it could provide a clue to extraterrestrial life, making it easier to search for life in the universe.'