"But we are also aware: There seem to be large boulders across most of Ryugu's surface and barely [any] surfaces with flat regolith," Ho added. "Although scientifically very interesting, this is also a challenge for a small lander and for sampling."

The $150 million Hayabusa2 mission launched in December 2014 and arrived at Ryugu on June 27 of this year. If all goes according to plan, the spacecraft will study the big asteroid from orbit for another 16 months and also drop down several times to grab samples of Ryugu material. 

Meanwhile, MASCOT and the three tiny, hopping rovers — known as Minerva-II-1a, Minerva-II-1b and Minerva-II-2 — will gather a variety of information about the asteroid from its surface. (Minerva-I flew aboard Japan's first asteroid-sampling mission, the original Hayabusa, which returned grains from the space rock Itokawa to Earth in 2010.)

The Hayabusa2 orbiter is scheduled to depart from Ryugu in December 2019. The capsule containing the mission's asteroid samples will come down to Earth a year later, in December 2020. 

Hayabusa2 isn't the only asteroid-sampling project underway. NASA's $800 million OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) mission is on its final approach toward the asteroid Bennu, and should arrive in orbit around the 1,650-foot-wide (500 m) rock this December. OSIRIS-REx's samples are due to land on Earth in September 2023.

Both Hayabusa2 and OSIRIS-REx aim to help scientists better understand asteroid composition and structure, the early history and evolution of the solar system, and the role space rocks may have played in helping life get a start on Earth. 

Bringing pristine samples of asteroid material back to Earth will allow researchers to tackle such questions efficiently and effectively, team members from both missions have said. Scientists can perform many more experiments and investigations using well-equipped labs around the world than a robotic probe could conduct all by itself in deep space.

Quelle: SC

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Update: 6.09.2018

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Boulders on the surface of asteroid Ryugu

Images from Hayabusa2 revealed many more boulders on the surface of asteroid Ryugu than were expected. Asteroid Itokawa also has a large number of boulders, but Ryugu appears to have more per unit area. Figures 1 and 2 show boulders marked in green that appear to be between 8 m to more than 10 m in size, based on images taken from the home position (about 20 km away from Ryugu) on June 30, 2018.

• Figure 1: Distribution of boulders on the surface of Ryugu (asteroid is pictured at 300 degrees longitude). A green marker indicates a boulder that appears to be between 8 m to 10 m or more. In this figure the north pole of the asteroid is at the image top.
  Image credit ※: Kindai University, JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University. University of Aizu, AIST.

Figure 1 shows a region of Ryugu’s surface where the boulder coverage is comparatively low. By contrast, Figure 2 shows a region where there seems to be far more boulders (although it is possible that this will change with more detailed analysis in the future). Both regions in Figure 1 and Figure 2 have hundreds of identified boulders, but there is also considerable variation between places where the boulder number is particularly high and regions where there are fewer. In general, boulders provide valuable evidence about the kinds of collision that an asteroid has been subjected to over its lifetime. The number, shape and variation of these boulders will therefore be examined in detail and, when compared with other observational data, allow the formation of asteroid Ryugu to be revealed.

• Figure 2: Distribution of boulders on the surface of Ryugu (asteroid is pictured at 60 degrees longitude). A green marker indicates a boulder that appears to be between 8 m to 10 m or more. In this figure the north pole of the asteroid is at the image top.
  Image credit ※: Kindai University, JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST.

※ Please use the displayed credit when reproducing these images. In the case where an abbreviated form is necessary, please write "Kindai University, JAXA & collaborators".

Tatsuhiro Michikami (Faculty of Engineering, Kindai University), Hayabusa2 ONC Team.
2018.08.31

Quelle: JAXA

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Is That the Death Star? Japanese Probe's Pictures of Ryugu Show a Divot on Top

Credit: National Astronomical Observatory, JAXA, Chiba Institute of Technology, Aizu Univ., Nippon Univ., Osaka Univ.

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That's no moon — it's an asteroid. New pictures of Ryugu, the target asteroid for Japan's Hayabusa2 landing mission, looks a bit like the infamous world-destroying "Death Star" spacecraft of "Star Wars" yore. And that's just one view of Ryugu recently sent to Earth by the probe.

Hayabusa2 is still measuring Ryugu's shape, but preliminary data from the probe's laser altimeter instrument shows that the spacecraft looks like a spinning top. However, there's a large divot at the top of the asteroid, which is reminiscent of the small hole on one hemisphere of the Death Star.

The difficulty with measuring Ryugu is it's very hard to track the orbit of the spacecraft, the Japan Aerospace Exploration Agency (JAXA) said in a statement translated to English using Google Translate.

Generally, scientists can map the shape of a world by tracking changes in the trajectory of an orbiting spacecraft, which is pulled "down" toward the asteroid in places of higher mass. But this is a difficult measurement to do with Ryugu, which is very small (roughly 3,000 feet across, or 900 meters).

While scientists refine Hayabusa2's trajectory, they're also picking up information on the surface to help prepare the spacecraft for several "touch-and-go" procedures to pick up soil and return it to Earth. Hayabusa2 will also deploy several landers and rovers to explore the surface — the first of those will approach the planet on Sept. 21 and Oct. 3.

From pictures taken 12 miles (20 kilometers) above Ryugu's surface, Hayabusa2 recently mapped out hundreds of rock masses that each have a diameter of between 26 feet and 33 feet (8 and 10 m).

"It turned out that there are more rock masses on the surface of the asteroid Ryugu than expected," JAXA officials said. Ryugu has more rocks in a given area than asteroid Itokawa, which was the target of the predecessor Hayabusa mission that concluded in 2010. Scientists are studying the masses closely to learn more about how Ryugu was formed, JAXA added.

Another piece of the formation process comes through understanding what minerals are on the surface of Ryugu. A preliminary map shows temperature differences on the asteroid taken with Hayabusa2's infrared camera. Already, scientists can see a marked temperature difference between the northern and southern hemispheres of Ryugu, although the reason is still under investigation. 

So far, scientists say the highest-temperature areas appear to be around 212 degrees Fahrenheit (100 degrees Celsius), while the lowest-temperature areas appear to be room temperature. While JAXA did not define what "room temperature" means, generally that indicates temperatures of about 68 to 77 degrees F (20 to 25 degrees C).

Hayabusa2 arrived at Ryugu on June 27 and is expected to make its first touch-and-go landing in October.

Quelle: SC

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Update: 11.09.2018

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Thermography of Ryugu by the TIR

We conducted observations of asteroid Ryugu using the Thermal Infrared Imager (TIR) onboard Hayabusa2. Figure 1 shows the thermographic image taken using the TIR at an altitude of 20 km (the home position) from Ryugu.

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• Figure 1: Asteroid Ryugu observed with the Thermal Infrared Imager (TIR). The images were captured between 16:02 – 23:45 JST on June 30, 2018 and were taken every eight minutes for one rotation. From the 20 km altitude (home position), one pixel is about 20 m in size. The distance to the Sun at this time is 0.987 au (1 au is about 1.496 billion km, the average annular distance between the Sun and the Earth). The scale bar shows relative temperature (the values have no meaning). Red indicates a high temperature while blue is for colder temperatures.
  Image credit ※: JAXA, Ashikaga University, Rikkyo University, Chiba Institute of Technology, University of Aizu, Hokkaido University of Education, Hokkaido Kitami Hokuto High School, AIST, National Institute for Environmental Studies, University of Tokyo, German Aerospace Center (DLR), Max Planck Society for the Advancement of Science, Stirling University.

The image shows the temperature differences on Ryugu's surface during one rotation, with red indicating regions with a high temperature. Distinct regions at different temperatures are captured by the TIR. Features in a thermal image can be seen even if they are in a shaded location in the visible photograph. This lets us confirm that the overall shape of the asteroid is well understood, and also the characteristic topography such as craters and large boulders that show up as a difference in temperature.

A temperature difference can also be seen between the north and south hemispheres of the asteroid. At present, it is summer in the southern hemisphere (the upper part of the figure) and the temperature is higher in this region. In the northern hemisphere in the lower part of the figure, it is currently winter and colder. This difference is due to the inclination of the rotation axis, which results in different levels of radiation reaching the north and south. The TIR has therefore spotted that asteroids also undergo a “seasonal change”.

High temperatures on the asteroid reach 100°C, while the coldest regions sit at about room temperature. Temperatures also change depending on the solar distance of the asteroid, lowering as Ryugu moves further away from the Sun.

During the Hayabusa2 mission, we will investigate the formation process of asteroids by examining the characteristics of the surface material revealed by differences in surface temperature. From the TIR data, we can also look for scientifically important landing sites with millimeter-sized grains, and avoid landing Hayabusa2 in severe temperature environments or locations with obstacles such as boulders.

Reference: An article by Takehiko Arai, member of the TIR team, was posted on the Ashikaga University website (Japanese only).

Quelle: JAXA, Ashikaga University & collaborators

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