On August 13, 2015, a shape model of Rosetta’s comet was released by ESA, along with a new interactive viewer that allows the public to explore the shape and surface of Comet 67P/Churyumov-Gerasimenko. In addition, close to 7,000 images taken with Rosetta’s NAVCAM navigation camera are available for download from the ESA Archive Image Browser, and that number continues to increase with regular additions of many more as the Rosetta mission continues. Since November 2014, these images have been released under a Creative Commons license, which allows them to be shared with anyone and published anywhere, and also allows users to adapt, process and modify them.
“At the most basic level,” the Rosetta Flight Dynamics team explained in a recent blog, “a shape model is a geometrical representation of an object. Shape models are commonly used in computer programmes where the motion or change of shape of a complex object needs to be represented. Applications can vary from medical imaging of organs, creating characters in cartoons and computer games, or — closer to home (at least for the Rosetta team) — modelling how the surface of a comet changes as it rotates.”
A year ago, as it became clear that this comet has an unusual shape, ESA “saw the need for an interactive way of exploring the surface of the comet. More recently, we started to wonder about what could be done with the Rosetta images and 3-D computer models of the shape of the comet.”
ESA project scientist Oliver Jennrich came up with a simple prototype tool using a shape model that had been developed by image processing expert and space enthusiast Mattias Malmer. Mattias used publicly available NAVCAM images to generate his model and then made it available via his own Web site. With this tool, users could zoom in and out, rotate and pan across the comet.
Over the next few weeks, new features were added, including a texture map made to add regions identified in scientific analysis of 67P/C-G, and a trail of points along Rosetta’s trajectory to show where images of the comet had been taken by NAVCAM — making it possible to link the tool to the NAVCAM database and to view and allow downloads of corresponding images.
Over time, the code was optimized and the interface was fine-tuned until a beta version was released to the public at the time of perihelion. (The period around perihelion is scientifically important, since the sunlight’s intensity increases, and parts of the comet previously cast in years of darkness are flooded with sunlight). The code is available as open source, and ESA is encouraging the public to take it and develop it further.