A surprising close-up of the asteroid Ryugu suggests it may have been too close to the sun
The article introduces astronomers studying the points in the photos of the asteroid "Ryugu" brought back by the Hayabusa2 probe and finding that the red material on the surface of Ryugu is caused by space weathering and solar radiation, while the red layer of Ryugu initially appears to be only a few tens of centimeters may be caused by being too close to the sun.
Just a year ago, at the end of February 2019, the Japan Aerospace Research and Development Agency (JAXA) accomplished an amazing feat. It took the Hayabusa2 probe to the surface of the asteroid Ryugu for sample collection before returning it to its original orbit.
Hayabusa2 took off again, and its camera captured something strange, a black smudge left on the surface of the asteroid by the probe's booster. Now those strange smudges help astronomers unravel the secrets of the asteroid Chiselze.
"These two different types of material exhibit different colors on the surface: bluer material is distributed in the equatorial ridge and the poles, and reddish material is distributed in the mid-latitudes. Yet they have not yet figured out the cause of this spectral difference. The researchers wrote in the article.
(Japan Aerospace Research and Development Agency, University of Tokyo & Partners)
With Hayabusa-2 landing at Ryugu on February 21, 2019, it managed to capture high-resolution photographs of the surface, able to distinguish details from millimeter to pixel.
"These images allow us to observe some of the reactions on its surface caused by physical disturbances that arise from the landing of the probe, including a strong collision like a missile explosion and the combustion of the exhaust port of the aircraft propulsion device." The research team wrote.
Images and observational information of the asteroid have made it clear that it exhibits a cat-like variegation, and the sample was partially extracted because it provides a mixture of blue and red materials.
But when Hayabusa2 flew back into orbit, the material was affected, and this seemed to be related to a redder substance, rather than a blue substance.
While studying the asteroid, the researchers also noticed some properties of the distribution of the two species. Larger rocks tend to be blue, while the finer-grained material around them — dirt and gravel — tends to be red. Craters filled with blue material were found to be younger than craters filled with red material, and it appeared that the impact penetrated the red layer at the top, revealing the blue surface below.
All of this suggests that the asteroid's rocks were originally on the blue side and turned red due to some sort of process.
It also showed that the process of small gravel turning red occurred longer than boulders were exposed through processes such as impact destruction or thermal fatigue.
Fortunately, we know the processes that can and do make asteroids red on a fairly regular basis: space weathering and solar radiation. This can continue for a long time, but compared to solar radiation, space weathering usually only turns a very thin surface layer a few nanometers red. It looks like the red layer of the "Dragon Palace" was initially only a few tens of centimeters.
(Morota et al., Science, 2020)
The researchers wrote in the paper: "We believe that if Ryugu underwent a temporary orbital shift near the Sun, resulting in higher surface temperatures, then this could explain the surface reddening event that occurred in a short period of time." ”
But scientists were also able to pinpoint the periods when this could happen. Its surface suggests that the asteroid is very young, only about 9 million years old. It began its life in the main asteroid belt between Mars and Jupiter, where collisions with other objects were more frequent than the low-Earth orbits that asteroids later entered.
Most of the large craters on the asteroid are red. This suggests that Ryugu only turned red after leaving the asteroid belt, where it experienced more frequent collisions.
A model estimates how the frequency of these collisions changes over time, allowing us to set a time area where reddishing occurs. If the reddishing occurred after the asteroid left the main belt, it could have occurred about 8 million years ago, depending on the number of large blue craters.
If the "Dragon Palace" stayed in this area, redness could have occurred 300,000 years ago.
Astronomers have a way to narrow it down. They could try to simulate the orbit of Ryugu back in time to see when it might have approached the sun. But the samples collected by Hayabusa2 during the landing process are expected to be very revelatory.
"The huge local variation in the spectral slope and albedo of the 'Ryugu' sampling point suggests that Hayabusa-2 may have collected bluer and redder components when it landed, the researchers wrote in the paper."
"We predict that the samples returned will contain a mixture of altered and unchanged materials, the former recording solar heating events."
The study was published in the journal Science.
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