The asteroid game is heating up. The Japanese probe Hayabusa 2 has arrived at asteroid 162173 Ryugu, the plan being to reach the surface with landers later this year and bring back samples in 2020. We also have ORISIS-REx, launched in 2014, on course to 101955 Bennu in December, with a sample return planned for 2023. Assuming both missions are successful, scientists will have the opportunity to compare the composition of the two. Both are C-type (carbonaceous) asteroids, darker than previously explored asteroid Itokawa. The current Hayabusa is similar to the probe that first returned an Itokawa sample to Earth in 2010.
JAXA confirmed the arrival of Hayabusa 2 at 9:35 (Japan time) on the 27th: “The National Research and Development Corporation Japan Aerospace Exploration Agency (JAXA) announces that we have confirmed the arrival at asteroid Ryugu (Ryugu) of the asteroid explorer ‘Hayabusa 2′”, adding that the distance between the spacecraft and the asteroid is about 20 kilometers.
From a JAXA statement:
The confirmation of the Hayabusa2 rendezvous made at 9:35 a.m. (Japan Standard Time, JST) is based on the following data analyses:
* The thruster operation of Hayabusa2 occurred nominally
* The distance between Hayabusa2 and Ryugu is approximately 20 kilometers
* Hayabusa2 is able to maintain a constant distance to asteroid Ryugu
* The status of Hayabusa2 is normal
Itokawa is an S-type asteroid, so this will be our first chance to sample a C-type, the closest previous encounter with the latter being the NEAR Shoemaker flyby of 253 Mathilde in 1997, which could not close to less than 1000 kilometers. Hayabusa 2 has already released an image of Ryugu from about 40 kilometers out. I liked the way project manager Yuichi Tsuda described the boulder-filled object:
“The shape of Ryugu is now revealed. From a distance, Ryugu initially appeared round, then gradually turned into a square before becoming a beautiful shape similar to fluorite [known as the ‘firefly stone’ in Japanese]. Now, craters are visible, rocks are visible and the geographical features are seen to vary from place to place. This form of Ryugu is scientifically surprising and also poses a few engineering challenges.”
Image: Closing on destination. This is asteroid 162173 Ryugu from a distance of roughly 40 kilometres. The image was taken by the spacecraft’s ONC-T (Optical Navigation Camera – Telescopic) on June 24, 2018 at around 00:01 JST. Credit : JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST.
I like the idea of a ‘firefly stone,’ and also note that the name Ryugu means ‘dragon’s palace’ in Japanese, giving the imagination plenty to play with. The science payoff from both Ryugu and Bennu could be significant. C-type asteroids are intriguing because they are assumed to be the source of carbonaceous chondrite meteorites and are thought to contain organic material as well as water. With a diameter of about 900 meters and a low-reflectance surface, Ryugu may not win any beauty contests, but it is conceivable that asteroids like this could be sources of water or oxygen that future space missions will tap.
Moreover, asteroids like these are expected to give us insights into objects in the early Solar System, and the samples gained by Hayabusa 2 and its landers should be able to tell us whether the asteroid’s dark surface is as rich in carbon as we assume. Of particular interest is the question of water. The isotopic and chemical analysis of Ryugu should help us gain insights into the formation of Earth’s oceans through incoming asteroids or comets. Landing site selection will be critical as the mission teams plans a 30 cm per second touchdown in October.
Tsuda goes on to note some of the challenges the early imaging is beginning to reveal. While the rotation axis of the asteroid is perpendicular to its orbit, there is a peak near the equator and various small craters, factors that will have to be considered as landing sites are assessed. The object’s unusual shape also introduces some issues:
Globally, the asteroid also has a shape like fluorite (or maybe an abacus bead?). This means we expect the direction of the gravitational force on the wide areas of the asteroid surface to not point directly down. We therefore need a detailed investigation of these properties to formulate our future operation plans.
Image: It looks like a big space diamond — but with craters. It’s 162173 Ryugu (Dragon’s Castle), and Japan’s robotic Hayabusa 2 mission is now arriving at this near-Earth asteroid. Ambitious Hayabusa 2 is carrying an armada of separable probes, including two impactors, four small close-proximity hoverers, three small surface hoppers, and the Mobile Asteroid Surface Scout (MASCOT) which will land, study, and move around on Ryugu’s surface. Most of these are equipped with cameras. Moreover, Hayabusa 2 itself is scheduled to collect surface samples and return these samples to Earth for a detailed analysis near the end of 2020. Pictured, a series of approach images shows features suggestive of large boulders and craters. Credit & Copyright: ISAS, JAXA, Hayabusa 2 Team.
Hayabusa 2’s distance from Earth is now 1.9 AU, with a round-trip light time of 1895 seconds.