Teamwork: Hayabusa2 and MASCOT and the role of the lander's camera
Hayabusa2 and MASCOT will make a first-class team when they start investigating Ryugu. While Hayabusa2 will observe the asteroid's surface from the home position and take soil samples, MASCOT will examine the asteroid surface directly on site. Our MASCOT camera, called MASCAM, plays an important role here, as it will take high-resolution images of the surface, while Hayabusa2 will later obtain soil samples that will be brought back to Earth. This is important in ensuring that the samples are later interpreted in the correct context in the laboratory on Earth. The pictures that the camera acquires of the surface thus serve as the bridge between the lower-resolution images provided by the Hayabusa2 probe, at a distance from the asteroid, and the laboratory images of the samples brought back to Earth.##markend##
What kind of camera is it?
The MASCOT camera was developed and built by the DLR Institute of Planetary Research together with Airbus Munich. MASCAM is a small, compact camera measuring 117 x 77 x 96 millimetres, and weighing 403 grams fitted with a wide-angle lens. It is positioned directly in front of MASCOT's 'feet', and looks obliquely downwards from this vantage point, with its view stretching to the horizon. At close range, it can pick up details on the surface at up to 0.15 mm. The sensor is a CMOS sensor with a resolution of one megapixel (1,024 × 1,024 pixels). These days, all standard mobile phone cameras offer higher resolution than this, but for space missions we have to opt for sturdy, proven technology able to withstand extreme conditions such as temperature and radiation. Moreover, the images that we want to transmit from MASCOT to Hayabusa2 cannot be too large, as it will take too long to transfer them. For this reason, the recordings are additionally compressed before being transmitted.
Image sensors in commercially available digital cameras have sensors with RGB colour filters that use the Bayer pattern. MASCAM is different. In order for the camera to be able to produce colour pictures, we have fitted it with an LED lighting unit made up of 4x36 LEDs, which can illuminate a narrow area directly in front of the lander in four different colours (red, green, blue, IR).
This has two advantages. The camera can also acquire images during the night or in shadow. Ryugu has no atmosphere, so there is no diffused light, with the result that it is completely dark in the shade of any boulders. We have included light-emitting diodes (LEDs) for this purpose, as they are able to light up the surroundings. This also allows us to take single exposures in different limited wavelength ranges. Taking images in all four of the wavelength ranges makes it possible to create images in natural colours. Single exposures of the surface in different colours show us different materials on the surface and their spatial distribution. As a rule, the soil on an asteroid appears greyish. However, colour variations give us clues as to changes on the asteroid surface. For instance, if reddish shades occur, this indicates oxidation (from iron in the rock), while bright white tones may suggest the presence of ice. Variations between blue and red, or green and red indicate that the surface has been weathered by radiation and bombardment by micrometeorites. Together with the data from the French infrared spectrometer MicrOmega, which measures the composition of the asteroid surface with precision, we can gain an accurate picture of the material present within the camera’s range of vision.
What are we looking to discover?
When MASCOT separates from Hayabusa2 on 3 October, MASCAM will already be switched on. The camera will take pictures at regular intervals during the descent and landing. If we are lucky, we will end up with a series of images of the asteroid as the lander descends to the surface. Why does luck come into it? MASCOT will be ejected from Hayabusa2 using a spring mechanism. If the lander does not separate completely smoothly and symmetrically, it may wobble and spin during the descent, which would mean that MASCAM will be looking in the wrong direction. So it will be a tense moment. After the impact, MASCOT is not likely to simply lie on the surface, but will first spring back up, then bounce around on the surface for a little while, depending on the properties of the soil, before coming to rest. MASCAM will also take images during this time. As soon as MASCOT is in its final landing place and has uprighted itself, the ‘on-asteroid’ phase will automatically begin, during which we will take pictures in different sequences throughout the day and during the night.
These images are not only intended to serve as reference and comparison pictures for the measurements performed by Hayabusa2 and the soil samples; we also want to glean considerable insights about the asteroid from them, for example about its composition, the physical properties and the condition of its surface, and the microstructure of the surface material. Combining and comparing our images with the measurements from the other MASCOT instruments will allow us to also learn something about the origin, structure and formation of Ryugu. Another example is the analysis of rocks on Ryugu. If MASCOT sets down on the MA-9 landing site as planned, MASCAM should have several large rocks within its range of vision, which we will be able to see side-on. Hayabusa2 is only able to see these rocks from above. As we can see them from the side, we can also look at the structure, fissures and cracks in the rock. By examining the fractures in a rock, we can deduce the tension within it and possibly also work out the impact velocity. In an interview, our Principal Investigator Ralf Jaumann already stated that he is particularly excited about these side-on views of large boulders, as such observations could also help to improve our understanding of how these rocks got here in the first place. “Are they inside the soil, or simply lying on the surface? Do they come from the inside of the asteroid or are they the remains of something that has broken up? We know that Ryugu was once bigger than it is now. How were these boulders formed?” Comparing our findings with measurements from another MASCOT experiment will also help us to examine the strength of the rocks. The MARA radiometer will measure the surface temperature. We know that the heat capacity of fine material is different from that of solid material. MARA can measure whether the temperature of the rocks within MARA and MASCAM's field of vision is different from that of the surrounding area. In other words, we can deduce the density of these rocks from the measurements indicated by the camera and the MARA experiment.
It's extremely exciting!