Samples from asteroid Ryugu are the most pristine pieces of our solar system ever studied and contain amino acids that could have given rise to life on Earth.
Scientists studying the samples, brought to Earth in December 2020 by Japan's Hayabusa 2 mission, released results of a lengthy chemical analysis at the Lunar and Planetary Science Conference 2022, which takes place in Texas and virtually this week. The samples, collected from the surface and subsurface of asteroid Ruygu in 2018 and 2019, reveal what the near-Earth asteroid is made of, providing insights into the earliest days of the formation of our solar system.
Hayabusa 2 collected 5.4 grams of rocky grains from Ryugu during two sampling touchdowns. While the first touchdown focused on samples from Ryugu's surface, the second used an impactor to create a small crater and stir up material from beneath the asteroid's surface, which was then captured by the probe.
"The Ryugu material is the most primitive material in the solar system we have ever studied," Hisayoshi Yurimoto, a geoscience professor at Hokkaido University, Japan, and leader of the initial chemical analysis team of the Hayabusa 2 mission, said at the conference.
Ruygu, Yurimoto said, is a CI chondrite asteroid, a type of stony carbon-rich asteroid with a chemical composition that is the most similar to that of the sun. These asteroids, rich in water and organic material, are a possible source of the seeds of life delivered to the nascent Earth billions of years ago.
But the samples from Ryugu are somewhat different compared to the other CI chondrites that the researchers have seen previously, those that have been found on Earth as meteorites. The Ryugy samples appear more "primitive" and have a chemical composition that is more similar to the material of the early solar system, Yurimoto added. That is because they were not changed by interactions with Earth's environment,
A team lead by Hiroshi Naraoka, of Kyushu University in Japan, which looked for organic matter in the samples from Ryugu, said in another paper presented at the conference that the Ruygu fragments contained more carbon, hydrogen and nitrogen than other known carbonaceous chondrite asteroids.
The analysis by Naraoka and his team also found more than ten types of amino acids in the samples, including glycine and L-alanine, which are the building blocks of proteins that living organisms produce based on their DNA code.
"We detected various prebiotic organic compounds in the samples, including proteinogenic amino acids, polycyclic aromatic hydrocarbons similar to terrestrial petroleum, and various nitrogen compounds," Naraoka said in his presentation. "These prebiotic organic molecules can spread throughout the solar system, potentially as interplanetary dust from the Ruygu surface by impact or other causes."
Scientists have known that CI chondrite asteroids contain amino acids including glycine and alanine since 2001 when an analysis of a meteorite known as Ivuna, which landed in Tanzania 1938, revealed their presence.
Due to the absence of weather and tectonic processes, the material in asteroids and its chemical composition has barely changed since the bodies were "born" in the early days of our solar system. Ancient space rocks, such as Ruygu, therefore enable scientists to peer into the past. By studying pieces of asteroids up-close, researchers can understand how the organic matter which now forms the basis of all life on Earth sprung into being from the molecular cloud that gave rise to the solar system some 4.6 billion years ago and how it evolved so long ago.
The Hayabusa 2 samples revealed that Ryugu, as we see it today, was born from a collision that shattered its parent asteroid and turned it into what scientists call a rubble pile, a loose collection of rocks and pebbles held together just by the power of gravity, a team led by Tomoki Nakamura of Tohoku University, Japan, said in another paper presented at the conference.
As the crystals found in the samples contain a lot of water, the parent asteroid of Ryugu must have formed "outside the CO2 [carbon dioxide] and H2O [water] snowlines," Nakamura and his colleagues said in the paper. A snowline is a distance from the emerging star where the temperature is cold enough for volatile compounds (such as water and carbon dioxide) to condense into solid ice grains.
The presence of water somewhat altered the chemical composition of Ruygu some 5.2 million years after the birth of the solar system, leading to the creation of the mineral dolomite, the researchers added.