アミノ酸さんの新発見しんはっけんに至いたる物語ものがたり――ベンヌ試料しりょうから読よみ解とく生命せいめいの起源きげん

A type of amino acid found in organisms on Earth, tryptophan, has been newly discovered in samples collected from the near-Earth asteroid Bennu.

Researchers at the National Aeronautics and Space Administration NASA announced this discovery in the journal of the National Academy of Sciences PNAS.

The sample is part of the rocks and dust collected by NASAs OSIRIS-REx spacecraft when it landed on Bennu in 2020 and brought back to Earth in 2023.

Bennus composition reflects the components of the early solar system, making it an important clue in the search for the origins of life.

In previous analyses, 14 out of the 20 types of amino acids found in all living organisms on Earth, as well as all 5 types of nucleotide bases that carry genetic information in DNA and RNA, have been discovered.

Japanese probes also discovered amino acids in samples collected from another asteroid, Ryugu, in 2019.

Amino acids have also been found in many meteorites that have fallen to Earth.

In a new study, although it has not yet been definitively confirmed, tryptophan was clearly discovered as the fifteenth amino acid.

Jose Aponte, an astrochemist at NASAs Goddard Space Flight Center who participated in the research, explained, The discovery of tryptophan on Bennu is a significant achievement.

Tryptophan has a complex structure among amino acids, and until now, it had never been found in extraterrestrial samples such as meteorites.

He also mentioned in an email that if it can be confirmed that tryptophan is naturally produced in space, it would mean that the basic building blocks of life had already been created in the early solar system and that an environment suitable for the birth of life was in place.

The name Bennu is derived from an ancient Egyptian god who symbolizes the sun, creation, and rebirth, and it has a diameter of about 500 meters.

According to NASA, Bennu was formed between 2 billion and 700 million years ago from fragments of a much larger parent body in the asteroid belt between Mars and Jupiter.

Its composition reflects the chemical makeup of the primordial solar system about 4.5 billion years ago.

Bennu has been orbiting around the Earth for about 1.75 million years and approaches the Earth approximately every six years.

According to the data, Bennu could collide with Earth in 2182.

The probability of causing a global cooling phenomenon is 1 in 2,700, or 0.037%.

Bennus components originate from material produced by supernova explosions before the birth of the solar system.

They were synthesized under the extremely high-temperature conditions at the time of the explosion, and then continued to undergo further changes under the influence of heat and radiation from the Sun as Bennu was formed.

Furthermore, many raw materials essential for life, such as ammonia and other minerals, have also been discovered. These can aid in the synthesis of molecules like amino acids, but they themselves are not life.

Dr. Angel Mojarro is an organic geochemist and a researcher at NASAs Goddard Space Flight Center, leading the new study. Its like a missing piece of the puzzle, he said.

Tryptophan is related to sleep quality and is one of the essential amino acids that humans cannot synthesize on their own, so it must be obtained from food.

Mr. Mohalo stated that further verification is necessary to determine whether the 50-milligram sample analyzed by the group actually contains tryptophan.

However, according to experts, the samples from Bennu are highly pure, and the possibility of contamination from Earth is extremely low.

Samples collected directly from the surface of Bennu have not undergone chemical composition changes caused by atmospheric entry like meteorites that fall to Earth, so they are considered to be much more reliable as a time machine for studying the early solar system.

According to Professor Dante Lauretta, an expert in planetary science and cosmochemistry at the University of Arizona, salt, minerals, and organic matter were discovered for the first time in the samples brought back by OSIRIS-REx, but these may be lost during atmospheric reentry.

He stated that, on Bennus parent body, liquids were distributed in various places and at different times, and that each location had its own unique chemical system.

Samples that retain these distinctive chemical systems indicate that, before life emerged on Earth, there existed a liquid rich in actively functioning organic matter.

According to Harold Morowitz, a pioneer in the study of the origin of life, the core molecules that make up living organisms can be regarded as fossils of molecules originating from the early solar system.

The discovery of tryptophan and other amino acids in samples from Bennu further supports this hypothesis.

Professor Sara Russell, a planetary scientist at the Natural History Museum in London, emphasizes that in order to get the full picture, it is necessary to have both the thousands of meteorites collected on Earth and the pure samples brought back by spacecraft.

I did not participate in this study, but she said, The discovery of tryptophan is particularly remarkable.

This cannot be seen in meteorites. It was probably lost during the process of passing through the atmosphere and falling to the ground.