Japan’s Hayabusa 2 closes in on diamond-shaped asteroid Ryugu

The closest view of Ryugu released so far, from a distance of only 100 kilometres (62 miles), on June 20, 2018, showing a rough diamond shape, craters and boulders, as well as a bright spot bear the top point of the diamond. Image Credit: JAXA/University of Tokyo/Kochi University/Rikkyo University/Nagoya University/Chiba Institute of Technology/Meiji University/University of Aizu/AIST

Japan’s Hayabusa 2 spacecraft is now rapidly approaching asteroid Ryugu, providing the first-ever close-up views of this near-Earth object. According to The Mainichi, a news source covering the encounter from Japan, the Japan Aerospace Exploration Agency (JAXA) said on June 24, 2018, that the Hayabusa 2 space probe has successfully completed a course adjustment and entered the final leg of its 4.5-year journey to the asteroid. Its planned arrival will be on June 27. Meanwhile, JAXA has also released a new set of images, showing a roughly diamond-shaped body – also being compared to a spinning top – with boulders and craters.

As of June 24, the most recently released images are from a distance of 220-100 kilometres (136-62 miles). A bright spot can be seen near the top point of the diamond (shades of Ceres?) and what may be an equatorial ridge, something seen elsewhere in the solar system as well, such as on Saturn’s moon Iapetus and several other Saturn moons (Atlas, Pan, Daphnis).

The images are already showing quite a bit of detail, and of course, they will only get better as the spacecraft gets even closer!

Ryugu is small, with a diameter of about 850-880 metres (2,788-2,887 feet), and has an appearance similar to the asteroid Bennu, which the U.S. spacecraft OSIRIS-REx will encounter in 2020. Hayabusa 2 will attempt to send both a small lander and rovers to the surface of the asteroid, as well as bring samples back to Earth for study.

Additional images from Hayabusa 2’s approach, from June 18-20. Image Credit: JAXA/University of Tokyo/Kochi University/Rikkyo University/Nagoya University/Chiba Institute of Technology/Meiji University/University of Aizu/AIST

On June 19, Makoto Yoshikawa, the Hayabusa 2 mission manager for JAXA, said in a statement:

“When I saw these images, I was surprised that Ryugu is very similar in shape to both the destination of the U.S. OSIRIS-REx mission, asteroid Bennu, and also the target of the previously proposed MarcoPolo-R mission by Europe, asteroid 2008 EV5. Bennu and 2008 EV5 are about half the diameter (and 1/8 the volume) of Ryugu, with rotation periods about half as long. In other words, these celestial bodies are small and rotating fast compared to Ryugu. On the other hand, Bennu is a B-type asteroid, which is very similar to C-type asteroids such as 2009 EV5 and Ryugu. Therefore there should also be common properties due to the asteroid type. So we have both differences and similarities that have combined to produce very similar shapes… why is that? I think this is very interesting. So far, the asteroids we have explored have been different in shape, so Ryugu and Bennu could be the first time two similar-shaped asteroids have been examined. It will be interesting to clarify exactly what this similarity means scientifically.”

Images from Hayabusa 2’s approach to Ryugu, from between June 17-18, 2018. Image Credit: JAXA/University of Tokyo/Kochi University/Rikkyo University/Nagoya University/Chiba Institute of Technology/Meiji University/University of Aizu/AIST

After Hayabusa 2 arrives at Ryugu, it will be only 20 kilometres (12.5 miles) above the asteroid’s surface. Between this coming September and July of next year, one small lander (called MASCOT-1) and three small rovers (called MINERVA-II) will be deployed to the surface. Before then, however, the spacecraft will need to study the asteroid to find the best landing locations. As Yoshikawa noted:

“If the axis of rotation for Ryugu is close to the vertical direction in this image, there is a big advantage as it will be possible to know almost the entire appearance of Ryugu at an early stage after arrival. This makes the project planning easier. However, it is also possible that potential landing sites may be limited to the equator of Ryugu. I hope we can find a suitable place to set down the lander and rovers.”

Ryugu is already proving to be an interesting body, as described by optical navigation camera principal investigator Seiji Sugita:

As we approached Ryugu and were able to distinguish individual features in the asteroid’s topology, it became clear that Ryugu has a land of rich terrain. Numerous clusters of rock roll on the surface. Among these, a large rocky mass (about 150 meters across) stands out on the upper part of Ryugu due to its brighter color (higher reflectivity). The belt-shaped ring of peaks that surround the equator are also slightly brighter than their surroundings. This colour difference may reflect a difference in material composition and the size of the particles that form the rock. We can also see many sunken regions that look like craters. These depressions may have been made in collisions with other celestial bodies. A structure that looks like a groove is also visible.

Artist’s concep of Hayabusa 2 at Ryugu. Image Credit: JAXA

The existence of such varied topographies is an indication that Ryugu has undergone a complex evolutionary history. It is generally believed that small asteroids that are less than 1 kilometre (0.6 miles), such as Ryugu, were created fairly recently in the solar system’s history (within several hundred million years) during the fragmentation of a larger parent body. Ryugu’s terrain will tell us about the division from the parent body and the asteroid’s subsequent evolution.

Hayabusa 2 is the second asteroid sample-return mission by JAXA. The first, Hayabusa, was launched in 2003 and arrived at the asteroid Itokawa in 2005. Despite some problems, 1,500 grains of rock from the asteroid were successfully returned to Earth in June 2010. Hayabusa 2 is scheduled to return its samples back to Earth in 2020.

Look for Hayabusa 2 updates here.

Want more details? Check out Scott Manley’s video, below:

This article was first published on EarthSky.



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