Detection of uracil in the asteroid Ryugu

The nearby small asteroid Ryugu is the third celestial body whose surface we have samples for detailed analysis in ground-based laboratories (the other two are the Moon and the Itokawa asteroid). The capsule of the Japanese probe Hayabusa2 landed in Australia in December 2020 with 5.4 grams of extraterrestrial matter from Ryugu. It may not seem like much, but thanks to today’s modern technologies, a lot can be extracted from this small amount. The latest published results confirm what we already suspected: that many asteroids are rich in complex organic material. A group of Japanese researchers led by Yasuhiro Ohba (Hokkaido University) discovered uracil and niacin (vitamin B3) in Ryugu samples.

Set of two sets of Ryugu samples (A0106) collected by Hayabusa 2 (JAXA/Nature).

As is known, uracil (C4h4no.2also2) is one of the four nitrogenous bases of RNA, so we are talking about one of the most important components of life. First of all, it must be clarified that similar compounds have already been detected in meteorites, but after contact with the Earth’s surface, there has been some debate as to whether we are dealing with a case of contamination with substances from our planet. In the case of Ryugu’s samples, the result is decisive and leaves no room for doubt. Specifically, Ryugu is a C-type asteroid, which is one that generates meteorites rich in carbon compounds classified as carbonaceous chondrites when they fall to Earth. For decades, it was thought that carbon-rich asteroids and comets were responsible for filling the early Earth with complex organic matter, giving rise to life. This finding reinforces this hypothesis.

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asteroid Ryugu. The arrow indicates the first sample collection area (Tamatpaco) seen in July 2018 (JAXA).
Sample sets A0106 and C0107 from Ryugu were analyzed for nitrogenous bases and other organic matter (JAXA/Oba et al.)

To analyze the Ryugu samples, the researchers had two sample batches, labeled A0106 and C0107, of 38.4 and 37.5 milligrams, respectively (A and C denote the sample chambers in which Ryugu was stored). Ryugu material; Camera B was not used because only two capture maneuvers were performed). The A0106 cluster was collected during the probe’s first contact with the asteroid and C0107 during the second. However, the full number of samples was not used in the analysis, but only about 10 milligrams from each group. Ryugu was first immersed in hot water at 105 °C for 20 hours and then in hydrochloric acid. Finally, they analyzed the bases generated by organic molecules and nitrogenous bases using liquid chromatography and high-resolution mass spectrometry. In sample A0106, uracil was found at a concentration of 11 ± 6 ppb and in C0107 at a concentration of 32 ± 9 ppb. Vitamin B3 is detected in higher concentrations. No other nitrogenous base was detected, but it was not ruled out that it was present in the samples and that it might be discovered later.

Comparing the spectrum of the Ryugu samples to other calibration samples, including the meteorite (Oba et al.).

The difference in uracil concentrations could be due to different exposures to ultraviolet light, cosmic rays, and the solar wind from the two groups, as C0107 has been within a meter of Ryugu’s surface for the past few million years. ejected by the Hayabusa 2 probe. According to an analysis of materials collected by Hayabusa 2, Ryugu is formed from the accumulation of fragments – a heap of asteroid rubble – after a collision with an asteroid larger than what was created during the origin of the solar system, 4.56 billion years ago, in the asteroid belt main (or away from it). 5 million years ago, Ryugu migrated to its current orbit, close to Earth. This study is not the first to look for carbon compounds in Ryugu samples, as analysis results have already been published that have led to the detection of several organic substances (some amino acids unrelated to terrestrial life, polycyclic aromatic hydrocarbons, carboxylic acids, alkylamines, etc.). ). It certainly wouldn’t be the last study to be done with Ryugu’s samples, either. Now it’s time to wait for September 24, 2023, which will be the day when NASA’s OSIRIS-REx probe capsule lands in Utah with more than 400 grams of material collected from the asteroid Bennu, another celestial body rich in organic matter. How similar will it be to Ryugo?

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The surface of Ryugu as seen by the MINERVAII-1A rover in 2018 (JAXA).



Lovell Loxley

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