As the Japanese Hayabusa2 spacecraft closes in on asteroid Ryugu, more details become visible to the planetary scientists. On 20 July 2018, from a distance of just six kilometres, the spacecraft’s Optical Navigation Camera - Telescopic (ONC-T) acquired an image of the asteroid’s surface, with its largest crater. "We see that the entire surface of Ryugu is strewn with large boulders – we have not yet seen this on an asteroid," says Ralf Jaumann, a planetary scientist at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and Principal Investigator for the MASCOT (Mobile Asteroid Surface Scout) lander aboard the Japanese spacecraft. It is anticipated that on 3 October 2018, MASCOT will land on Ryugu and examine the asteroid surface using four instruments.
Descending towards the asteroid
Since Hayabusa2’s arrival at the asteroid on 27 June 2018, the JAXA - GLOBAL had operated it at a height of 20 kilometres (the Home Position) above the surface. But on 16 July, the JAXA engineers slowly lowered Hayabusa2 from this observation position, until it was six kilometres above Ryugu. The resolution of the images is approximately 3.4 times greater than in the pictures acquired from the Home Position – one pixel now corresponds to about 60 centimetres. A particularly large crater is visible near the centre of the image.
For Jaumann, the images coming from some 300 million kilometers away give the opportunity to get a first impression of the asteroid: "It is likely that Ryugu is a fragment of an earlier collision. However, we have only just been at the asteroid for a short while – and all we can see is the surface.” How old is the asteroid? What is its interior like? How dense is it? Is it made up of several agglomerated pieces of debris or is it just one large piece? These are all questions that the planetary scientists want to discuss and answer.
Preparations for the landing
On 25 July 2018, the Hayabusa2 probe returned to its previous position 20 kilometers from Ryugu. In August 2018, the probe will then be lowered again to a distance of approximately one kilometre from the asteroid’s surface to measure its gravitational field, which is estimated to be just 1/60,000th of Earth's. The detailed photographs of the 900-metre-diameter Ryugu and the determination of its gravitational field are also important for the selection of MASCOT’s landing site. At the end of August, the site will be determined by all involved international scientists and engineers. During the mission, Hayabusa2 will also descend to the asteroid’s surface several times and collect soil samples. At the end of 2019, the Japanese probe will begin its return journey to Earth, where it is expected to arrive in 2020 with the asteroid samples.
About the Hayabusa2 mission and MASCOT
Hayabusa2 is a Japanese space agency (Japan Aerospace Exploration Agency; JAXA) mission to the near-Earth asteroid Ryugu. The German-French lander MASCOT on board Hayabusa2 was developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and built in close cooperation with the CoRoT Special. DLR, the Institut d'Astrophysique Spatiale and the Technical University of Braunschweig have contributed the scientific experiments on board MASCOT. The MASCOT lander and its experiments are operated and controlled by DLR with support from CNES and in constant interaction with the Hayabusa2 team.
DLR Institute of Space Systems in Bremen was responsible for developing and testing the lander together with CNES. The DLR Institute of Composite Structures and Adaptive Systems in Braunschweig was responsible for the stable structure of the lander. The DLR Robotics and Mechatronics Center in Oberpfaffenhofen developed the swing arm that allows MASCOT to hop on the asteroid. Das DLR Institute of Planetary Research in Berlin contributed the MasCam camera and the MARA radiometer. The asteroid lander is monitored and operated from the MASCOT Control Center in the Microgravity User Support Center (MUSC) at the DLR site in Cologne.