Asteroids, remnants from the solar system's formation, hold critical data about planetary evolution. Among them, asteroid (162173) Ryugu, a 1 km-wide near-Earth object, has drawn attention due to its unique characteristics and position, crossing Earth's orbit at a distance of 300 million km.
Recent findings published in The Astrophysical Journal highlight the damaging effects of micrometeoroids on Ryugu. Japan's Aerospace Exploration Agency (JAXA) launched the Hayabusa2 spacecraft for remote sensing and sample collection from the asteroid in 2018 and 2019. Analyzing the samples revealed a distinct dehydration pattern in phyllosilicates, particularly in minerals like serpentine and saponite.
Dr. Daigo Shoji from JAXA emphasized that micrometeoroids as small as 2 nanometers can inflict significant damage on Ryugu, propelled by solar wind plasma magnetic fields. These particles reach speeds of approximately 400 km/s, leading to chemical reactions that are too rapid to observe directly.
Simulations conducted by Dr. Shoji's team revealed that impacts from larger cometary bodies at ~20 km/s resulted in around 200 broken oxygen-hydrogen bonds, while nano-sized dust particles impacting at ~300 km/s increased this number to 2,000. The resulting impact craters were minuscule, with the lower-velocity case producing a crater of just 4.4 nanometers.
The research also examined temperature effects on Ryugu's surface, which fluctuates between ~310 and ~340 Kelvin during the day and can drop to 200 Kelvin at night. Despite these variations, dehydration of minerals was not significantly affected. Instead, the energy from high-velocity impacts, exceeding 1,000 Kelvin, was found to be a crucial factor in the chemical reactions leading to bond breakage.
Interestingly, the dissociated atoms may recombine to form water and silanol functional groups, potentially counteracting the dehydration caused by micrometeoroid bombardment. This research not only enhances understanding of Ryugu's geological processes but also informs future missions targeting similar celestial bodies.