The fragments collected by the Japanese spacecraft Hayabusa 2 provide valuable information about a body almost as old as the Solar System
Launched in late 2014, the Japan Aerospace Exploration Agency (JAXA) Hayabusa 2 mission spent most of 2018 and 2019 studying Ryugu. The composition of this asteroid, rich in carbon, made scientists think that they could find traces of water and organic matter there.
In February 2019, the probe fired a projectile made of a metal called tantalum onto the ground of the asteroid, which impacted at 300 meters per second. The particles detached from the soil were collected by a special instrument that, in December of that same year, he sent to Earth a sample of 5.4 grams (with 10 mm rock fragments) that would reach the atmosphere a year later.
This Thursday a special number of Science details the analyzes performed on those samples, with two new studies describing the composition and structure of organic moleculesplus a review of three studies already published last summer.
In the first unpublished article in Science, the scientists detail that the Ryugu samples contain rock fragments dominated by minerals similar to clay, such as serpentine and saponite, as well as carbonates, sulfides and magnetite. The Ryugu samples date to the earliest stages of the Solar System, about 4.565 million years ago, when a warm, water-rich fluid seeped through the asteroidconverting the primordial components of the Solar System into the minerals that are now found within it.
The published works allow to reconstruct the astrochemical history of Ryugu. The authors explain that some of the organic molecules identified were formed in the interstellar medium (a set of matter and energy that exists in space) and that They predate the formation of the Solar System..
Two million years after our planetary system began to form, some of the material in the outer region collapse due to gravity to form a solid object (planetesimal), identified as Ryugu’s parental body.
Three million years later, the decay of radioactive elements raised its internal temperature enough to melt frozen water, which reacted with the rock for millions of years, until the temperature dropped again. Those interactions modified the geology and formed additional organic molecules in the celestial body.
About a billion years later, an impact on that parent body ejected material into space; part of those fragments accumulated under gravity to form Ryugu. Does slo about five million years gravitational disturbances caused the migration of the asteroid to its present near-Earth orbit.
Organic chemistry on the back of an asteroid
As for the second study, led by Hikaru Yabuta, a professor at Hiroshima University, the researchers analyzed soluble organic molecules taken from samples of Ryugu and identified amino acids, amino aliphatics, carboxylic acids, and polycyclic aromatic hydrocarbons.
The identified molecules shared properties with the organic remains found in carbonaceous meteorites fallen on Earth. According to the authors, the findings demonstrate that this type of organic molecules can survive on the surface of asteroids charred, despite the harsh conditions in space.
“It is surprising that prebiotic molecules such as amino acids and acetic acid can survive in such severe conditions, their presence suggests that grains on the upper surface may shield organic molecules“, Explain Hiroshi Naraoka, a researcher at Kyushu University (Japan). “These molecules can be transported throughout the Solar System, potentially being scattered as interplanetary dust particles after being ejected from the asteroid’s top layer by impacts or other causes. Humanity could even use such organic molecules as a resource in the future.”
In addition, the analyzes underscore the value of space missions. “Small asteroids are material left over from the formation of the Solar System. Their samples can provide information about the processes that took place during that period,” writes Christopher DK Herd of the University of Alberta (Canada) in a commentary in the same issue.
“These missions are revolutionizing scientific knowledge of planetary bodies from which the samples have been obtained and point the way for other missions, such as OSIRIS-REx -which is returning with samples from the carbonaceous asteroid Bennu- or the international effort to bring back samples from Mars”.
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