High-Resolution Images Of Asteroid Ryugu Reveal Origin Of Its Mysterious Surface Color

 Rear view of the Hayabusa2 probe. DLR German Aerospace Center. Credit: DLR (CC-BY 3.0)

A new investigation into images of asteroid Ryugu last year holds the key to the mystery of the space rubble’s surface color. The team of astronomers found one type of material on the asteroid's surface was redder, while the other was slightly blueish. The reason for this difference puzzled astronomers – until now.

Millions of asteroids orbit our Sun, the shattered remnants of cosmic objects from the dawn of our Solar System. Despite this, the total mass of all the space rubble in the asteroid belt combined is still less than that of our Moon. One of the most common and ancient types of asteroids are C-type, composed of clay and silicate rocks, including Ryugu. 

To learn more about this enigmatic period of creation, the Japanese space agency sent their Hayabusa2 spacecraft on a 42-month journey to Ryugu. In February 2019, the robotic space probe finally touched down on the asteroid's diamond-shaped body, snapping high-resolution images and collecting samples. To the team’s surprise, they found two types of material on the surface, one slightly redder and the other slightly bluer in color. 

Team lead Tomokatsu Morota and colleagues used the images and video to investigate the geology of the asteroid. They believe the reddening is due to a short period of intense solar heating, possibly caused by the asteroid taking a temporary turn towards the Sun. The results are published in the journal Science.

 

"Using image data obtained during the touchdown and in the global observation, we investigated the spatial distribution and the stratigraphic relationship of the redder and bluer materials on Ryugu's surface," Morota, from Nagoya University and the University of Tokyo, told IFLScience. "We found the latitudinal distribution of redder materials, suggesting that these redder materials were produced by solar radiation. Based on the stratigraphic relationship between identified craters and the redder material we also found that surface reddening occurred over a short period of time. These results suggest that Ryugu underwent an orbital excursion near the Sun."

Ryugu is made of material dating back to the formation of the solar system 4.5 billion years ago, but previous research found the surface itself is just 9 million years old. The team hope that by studying asteroids like Ryugu, which act as a time capsule of sorts, we can gain greater insight into the early Solar System and what materials were available for the development of life. 

"Ryugu is a primitive carbonaceous object and contains hydrated minerals and organic molecules. How such molecules changes chemically by solar heating is important for understanding the chemical evolutions of organic molecules, which may have been transported to the early Earth," said Morota.

"We will be able to place constraints on the chemical evolutions of organic molecules based on detailed laboratory analyses of these returned components of Ryugu."

Hayabusa2 is currently making the 300-million-kilometer (186-million-mile) trek back to Earth with an estimated return date of December 2020.

The surface of asteroid Ryugu, as observed by the Hayabusa2 spacecraft just before its landing. The spacecraft's solar ray paddle casts a shadow on Ryugu's surface. [Credit: JAXA/U. Tokyo/Kochi U./Rikkyo U./Nagoya U./Chiba Inst. Tech./Meiji U./U. Aizu/AIST]
Asteroid Ryugu photographed from a distance of about 12 miles (20 kilometers). Credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu and AIST.
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