Source: JAXA

Japanese spacecraft ‘Hayabusa 2’ sent spectacular photos of the surface of Ryugu asteroid. On February 21, 2019, the spacecraft touched the surface of the asteroid and sent images to the researchers.

The images gave a close look into the surface of the asteroid. They would help the astronomers and researchers get a better idea about the age and geographical history of the asteroid and planets. The images would also give better insight into the materials and process of formation of planets. The colouration of dust grains as disturbed by the landing hints at periods of rapid heating by the Sun in the process of an orbital sweep brought the asteroid closer to our star. The discovery also has implications for the orbits of other asteroids located in the solar system. ‘Our results suggest that Ryugu underwent an orbital excursion near the Sun,’ says Tomokatsu Morota, Nagoya University, Japan, and an author on the study. “This constrains the orbital transition processes of asteroids from the main belt to near-Earth orbit.”

The Hayabusa2 spacecraft descended on the surface of Ryugu after months of careful observations and operations to select a suitable landing spot on the carbon-rich asteroid. The primary mission of the craft was to collect samples that would be returned to Earth for researchers to analyze, making it the first sample-return mission from a carbonaceous asteroid. The researchers also aimed at learning the effects of artificial impacts on the asteroid’s surface. “The most important objective of the touchdown is sample collection from Ryugu’s surface,” Morota explains. “We are sure that Hayabusa2 successfully conducted the sample collection from the observation showing a large number of fine grains lifted in the touchdown operation.” Even as researchers have to wait for the return of Hayabusa2 and samples, Morota and team can already state much about Ryugu from characteristics of dust as disturbed by the craft’s touchdown.

The observations of asteroid Ryugu was done before the landing of Hayabusa2. JAXA launched the Hayabusa 2 spacecraft in the year 2014. The observations indicated that the asteroid consisted of two different materials- one redder in hue and the other slightly bluer. These observations were confirmed upon the touchdown of the probe. ‘Using the high-resolution images obtained in the touchdown operation, we found that a large amount of red, dark fine grains was lifted from Ryugu’s surface by the Hayabusa2’s landing,’ Morota tells me. ‘The red, dark fine grains were produced by solar heating, suggesting that Ryugu underwent an orbital excursion near the Sun.’

Morota further explains that the variation in color of the asteroid is the result of some undergoing heating of the grains, while others did not. He explains that he expects Hybuas2 to have collected both types of grain from the asteroid: ‘We found the large local variations in the spectra and albedo within the landing site, suggesting that both heated and unheated components were likely collected during the touchdown.’

The fact that Hayabusa2 spacecraft has collected both unheated and heated samples from the asteroid is vital to the objectives of Morota and his fellow researchers. ‘Ryugu is a primitive carbonaceous object containing hydrated minerals and organic molecules,’ the researcher says. ‘We’re interested to see how such molecules change chemically as a result of solar heating.’

This kind of observation and detailed information is available only from asteroids, which contain matter that closely reflects the raw materials from which solar system planets have formed initially. ‘In terrestrial planets, the primitive materials were once melted, and we cannot access older information,’ Morota says. ‘On the other hand, asteroids represent ancient material, surviving from the early solar system.’ The researcher and his team will also study Ryugu’s craters, craters that are formed from multiple impacts with other asteroids. This would help them to understand the tensile strength of the rocks from which it is formed and subsequently give clues about the impact history of Ryugu and smaller bodies in both the central asteroid belt and in orbit around Earth.

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