Could asteroid grains be at the origin of the first building blocks of life on Earth? This is what recent discoveries from space dust suggest. These fragments, brought back by a Japanese probe, could upend our understanding of the origin of life.
The return of these extraterrestrial samples to Earth in 2020 opened the door to new hypotheses. These grains taken from Ryugu, an asteroid located beyond Jupiter, contain crucial elements for the formation of biological molecules.
Artist's rendition of the Hayabusa probe skimming the asteroid, in 2018 / Japan Aerospace Exploration Agency (JAXA)
In 2014, the Japanese space agency JAXA sent the Hayabusa2 probe to Ryugu, a carbon-rich C-type asteroid. The goal? To collect surface samples in order to learn more about its composition.
Researchers used a specially designed chamber to handle these fragments, enabling analysis via spectral microscopy under vacuum. The samples, placed on gold-coated mirrors to prevent contamination, revealed a significant surprise: the presence of hydrated compounds, including magnesium, ammonium, and phosphorus.
These elements, particularly phosphorus, play a vital role in Earth's biology. Found in nucleic acids like DNA and RNA, they are the very foundations of life as we know it. The fact that grains from Ryugu contain these suggests that asteroids may have seeded Earth's surface with these chemical building blocks billions of years ago.
The analysis also showed that these particles come from distant regions of our Solar System, beyond Jupiter. If they had formed closer to the Sun, they would have evaporated due to the heat. This strengthens the idea that asteroids can transport valuable molecules through space, even over long distances.
Analysis of a particle extracted from a Ryugu sample, performed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).
Credit: Nature Astronomy (2024).
The discovery of ammonium in these samples further supports this hypothesis. This compound, capable of releasing hydrogen and nitrogen when it decomposes, is also crucial for biological processes. It becomes plausible, then, that these elements were incorporated into the earliest terrestrial organisms.
These results represent a significant advance in understanding the origin of chemical compounds that may have sparked life. If asteroids contributed to the formation of the first organic molecules on Earth, our entire conception of the evolution of life could be reevaluated.
The asteroid Ryugu and the Hayabusa2 mission
The asteroid Ryugu is a carbon-rich C-type body located about 186 million miles (300 million kilometers) from Earth. It follows an orbit similar to that of our planet, making it an ideal target for space exploration. This type of asteroid is particularly interesting because it contains primitive materials from the Solar System.
Ryugu contains organic compounds and hydrated elements like magnesium and phosphorus. These materials are crucial because they may have played a role in the emergence of life on Earth. The discovery of such elements in these samples strengthens the hypothesis that asteroids delivered the first chemical building blocks necessary for the formation of living organisms on Earth.
In 2014, the Japanese space probe Hayabusa2 was sent to Ryugu by the Japan Aerospace Exploration Agency (JAXA). The mission aimed to gather samples from its surface and debris resulting from collisions triggered by the probe. The collected materials were then brought back to Earth in 2020, where they are being studied by researchers around the world.
Scientists have identified compounds such as ammonium and phosphorus in the samples. Ammonium, when it decomposes, releases hydrogen and nitrogen, fundamental elements for biological chemistry. As for phosphorus, it is essential for forming molecules like DNA and RNA, the pillars of cellular life.