Ryugu is a near-earth asteroid that orbits the Sun between Earth and Mars while occasionally crossing the Earth’s orbit. This makes the celestial body a potentially hazardous object despite not posing any imminent danger to our planet.
A Japanese mission voyaged this near-earth asteroid wherein the spacecraft Hayabusa-2 collected samples from the asteroid’s surface in 2019. On December 6, 2020, those collected samples were brought back to Earth in an airtight container. Scientists have been engaged in analysing the samples, and recently (on December 21), they have reported their findings in two papers published in the journal Nature Astronomy.
The asteroid contains some of the darkest and oldest material known in the solar system, according to the reports published. The sample collected from the outer surface of Ryugu weighs a total of 5.4 grams. The rock samples have been found to contain many minerals and compounds similar to those found in meteorites on Earth. What makes the sample unusual is the presence of some compounds, such as organic compounds and water containing molecules.
Commenting on the samples, Cedric Pilorget of the University of Paris-Saclay, who was among the researchers involved in studying the sample, said, “Although most of these compounds are minor in terms of quantity – a few per cent at maximum – they have a high potential in tracing some of the processes that occurred in the earlier stages of the formation of the solar system and, later on, Ryugu’s parent body.” However, the exact age of the sample remains unknown, which is expected to be deciphered in future studies.
Ryugu is thought to be a C-type asteroid, meaning it contains carbonaceous compounds (containing carbon). Like other C type asteroids, it is likely that Ryugu also contains material from the nebula (a giant cloud of dust and gas) that gave birth to the Sun and its planets. This event, scientists think, took place billions of years ago.
The largest particles of the rock in the Ryugu sample measured around 8 millimeters across, with the smallest ones having a diameter of around 1 millimeter, which is same as fine dust particles. Toru Yada, a researcher at the Japan Aerospace Exploration Agency and a lead author of one of the two publications, explained to Livescience the appearance of the particles. He said, “To the naked eye, the samples look like incredibly dark bits of black pepper.”
The team led by Yada kept the material inside a vacuum chamber having a sealed environment filled up with purified nitrogen. In this way, the researchers kept the sample away from the Earth’s atmosphere. They used optical microscopes and various instruments to assess how the rocks absorb or emit or reflect light of different wavelengths in the visible and infrared spectra.
The researchers found that the extreme dark asteroid was found to reflect only 2% to 3% of the light that falls on them. Another interesting fact that the researchers found was that the density of the sample was lower than that of the known carbonaceous meteorites. The findings are suggestive of the fact that the rocks are highly porous, which mean that there exist many pockets between the individual grains of materials in the rocks. These empty spaces (the pockets) in the material may allow water molecules and gas to seep. These findings on Earth also align with what the preliminary data collected by Hayabusa-2 suggested, which is that the rocks on Ryugu’s surface are porous in nature.
The samples from Ryugu are among the darkest ones that have ever been examined. Additionally, the researchers detected a trace of ammonia-rich compounds in the rock, which can help us understand the origin of Ryugu and our understanding of primordial material, according to the researchers.