Having amino acids does not mean having life
Recently, the Japanese Ministry of Education, Culture, Sports, Science and Technology announced that scientists have detected over 20 types of amino acids in samples collected by the asteroid probe "Hayabusa 2". These samples are from the exploration of the asteroid Ryukyu by Hayabusa 2 in 2020. According to Kenzo Kobayashi, honorary professor of astrobiology at Yokohama National University in Japan, the discovery of multiple amino acids on celestial bodies beyond Earth is "unprecedented" and may even suggest the existence of life beyond Earth.
Is the discovered amino acid really that miraculous? Several experts responded to the China Science Journal, pointing out that this is not the first time that humans have discovered amino acids in extraterrestrial materials, and it is currently difficult to summarize new discoveries in extraterrestrial exploration using the term 'life or non life'. However, the samples brought back by Hayabusa 2 can help scientists understand the important scientific question of the origin of early life on Earth, what the Earth may have been like during pre life periods, and how the first proteins were formed without the involvement of life.
This is not the first discovery
Regarding the amino acids detected in the surface samples of the "Dragon Palace", Ji Jianghui, a researcher at the Purple Mountain Observatory of the Chinese Academy of Sciences, stated that this is not the first time scientists have discovered amino acids outside of Earth.
In the Murchison meteorite that fell to Australia in 1969, scientists discovered over 100 types of amino acids. However, due to the possibility of contamination from Earth, there is insufficient evidence for the existence of extraterrestrial amino acids. In addition, scientists have discovered the existence of the simplest amino acid, glycine, in Sagittarius B2, Orion KL, and W51.
In 2015, the Philae lander carried by the Rosetta spacecraft discovered key components of life, such as nitrogen and amino acids, on the Churyumov Gerasimenko comet. Scientists have previously discovered amino acids multiple times in asteroid meteorite samples.
However, compared to previously studied meteorites, the samples collected from these extraterrestrial bodies in their natural state are very unique. Moreover, this batch of "Dragon Palace" samples comes from the subsurface of asteroids that are not eroded by sunlight or cosmic rays, and the sample analysis was conducted without exposing them to Earth's air.
Amino acids are components of proteins. There are two theories about where the first amino acids on Earth came from: formation on Earth and formation in space. One theory suggests that amino acids were brought to Earth from space by meteorites, and amino acids have been previously detected in meteorites; But there are also claims that the Earth already had amino acids, and the amino acids found on meteorites were attached after they fell onto the Earth.
Zhu Jin, Honorary Director of the Beijing Planetarium and Chief Scientist of the Science Communication Center of the Beijing Academy of Science and Technology, stated that water, amino acids, and other substances on Earth could potentially reach the Earth's surface through the impact of asteroids (small celestial bodies). The discovery of "Hayabusa2" is a form of support for this viewpoint.
Not the only criterion for judgment
Whether there is life or not, amino acids are not the only criterion for evaluation.
Shen Jianxun, a postdoctoral fellow at the Institute of Geology and Geophysics, Chinese Academy of Sciences, pointed out that amino acids are divided into two types: those that can synthesize biological proteins and those that cannot. Any organic compound with amino and carboxylic acid functional groups can be broadly referred to as an amino acid.
The amino acids currently discovered in biological proteins are 23 types of alpha amino acids with left-handed rotation and specific branched chains. Except for some derived amino acids formed by post-translational modifications of proteins, thousands of other amino acids cannot provide building blocks for proteins in Earth's organisms. ”Shen Jianxun emphasized.
According to reports, the amino acids discovered in the "Dragon Palace" include essential human amino acids such as isoleucine and valine.
In addition, scientists have also discovered glycine as a collagen material and glutamic acid, which is widely known as a flavoring ingredient, as well as various non protein amino acids.
The structural proteins of known life on Earth are synthesized from left-handed amino acids as the basic building blocks, and this choice of left and right handedness almost only occurs in living organisms. Amino acids formed through non living processes in nature or laboratories are usually 'left-handed' and 'right-handed', with each accounting for half. "Shen Jianxun said, just like discovering a brick does not necessarily mean there must be a building there, detecting chemical substances that can form life does not mean there is life, and it cannot be inferred how long it will take to form life.
He pointed out that given that we only understand the characteristics of life on Earth, this may limit our predictions about the forms of extraterrestrial life. Therefore, it is difficult for us to summarize new discoveries in extraterrestrial exploration based on the presence or absence of life, and we can only describe these phenomena based on the complexity of chemical systems.
Asteroid exploration is accelerating
Why do scientists focus their attention on the 'Dragon Palace' when there are so many asteroids in space?
Dragon Palace "is a carbonaceous asteroid (C-type asteroid) with a diameter of about 900 meters, formed by numerous large and small stones gathered together by their own gravity. Ji Jianghui stated that based on previous observations of Ryukoku by Hayabusa 2, there are traces of hydrated minerals inside the asteroid. Perhaps this is evidence that "water" was brought to Earth from interstellar space, and the origin of life may have come from the asteroid.
Shen Jianxun pointed out that the high diversity of amino acids in extraterrestrial celestial bodies and possible interstellar transmission pathways are indeed exciting in the field of astrobiology, indicating that Mars, which is similar to Earth, may also have a diverse range of organic molecules beneath its surface. Therefore, the discovery of the "Dragon Palace" has further stimulated scientists' motivation and sense of mission in exploring signals of Martian life.
Asteroid exploration has always been a popular research direction. In addition to Japan's Hayabusa 2, in 2023, the US probe Osiris REx will collect samples from the asteroid "Bennu" and send them back to Earth.
Zhang Rongqiao, the chief designer of China's first Mars exploration mission, stated in a media interview that the Tianwen-2 asteroid probe has entered the initial sample development stage and is expected to be launched in 2025, achieving the first retrieval of samples from Earth's "quasi satellite".