Georeferenced M-CAM images from BepiColombo’s first Mercury swingby

Auteur

Institution

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Abstract

On 1st October 2021, the ESA/JAXA BepiColombo spacecraft completed its first Mercury swingby. Closest approach was at 23:34 UTC at 199 km altitude. Two of the three engineering Monitoring Cameras (M-CAMs) on BepiColombo’s Mercury Transfer Module captured images of Mercury. Since BepiColombo approached on Mercury’s nightside, only images captured later than five minutes after closest approach, when the spacecraft’s altitude had risen to ~1180 km, observed the planet’s illuminated surface. Illumination varies from local dawn to noon across these images, which include tracts of the Kuiper and Discovery quadrangles. In this work, we georeferenced four M-CAM images and compared them with MESSENGER data.

We used ArcGIS Pro to georeference M-CAM images. To minimise projection distortions, we used individual “Vertical Near Side Perspective” projections for each image. These simulate a planet’s surface as seen from a spacecraft’s altitude along camera boresights. We used manually placed control point networks to georeference the M-CAM images to MESSENGER MDIS basemaps. With this approach, we created accurately georeferenced products and we were able to check for surface changes since the MESSENGER images were taken.

The first M-CAM2-M-CAM3 image pair (images 1 and 2), taken ~5 minutes after closest approach, shows the Kuiper and Discovery quadrangles with high incidence angle solar illumination, highlighting lobate scarps such as Astrolabe Rupes. The second image pair (images 6 and 8) shows more of the Kuiper and Discovery quadrangles, with mutual overlap resulting in a continuous view of Mercury’s terminator. We searched for MESSENGER images of these locations taken under similar illumination conditions. We found that there are not many equivalent images, which means BepiColombo has imaged parts of the Kuiper and Discovery quadrangles uniquely. For example, MESSENGER WAC image EW07617663G has similar illumination conditions to, but lower spatial resolution (2593 m/pix) than, MCAM image 1 (1370 m/pix) where they overlap.

There will be five more swingbys of Mercury before orbital insertion on 5th December 2025. M-CAM will capture new images of Mercury covering a range of latitudes and longitudes, under various illumination conditions. We will use these to identify and interpret features not, or imperfectly, revealed in MESSENGER images and to revise recent geological mapping. This will be particularly important for fault scarps and catenae, whose detection is highly dependent on illumination conditions (1). M-CAM images will also be useful for defining BepiColombo observations, particularly those of the SIMBIO-SYS instrument (2).

(1) Fegan, E. R. et al. (2017). Late movement of basin-edge lobate scarps on Mercury. Icarus, 288, 226-234. https://doi.org/10.1016/j.icarus.2017.01.005.
(2) Cremonese, G. et al. (2020). SIMBIO-SYS: scientific cameras and spectrometer for the BepiColombo mission. Space Science Reviews, 216. https://doi.org/10.1007/s11214-020-0