David Valls-Gabaud, from Observatoire de Paris, gave a presentation at NAOC on July 16, 2014. In his talk, he said that low surface brightness objects are the last unexplored frontier in observational astronomy because these objects are difficult to observe with ground-based telescopes. According to Valls-Gabaud, ground-based telescopes have approached a barrier in terms of their limiting magnitude of 29.5, regardless of their size, because of a combination of atmospheric effects and diffraction. To overcome this limit, he described the proposed MESSIER satellite which would be jointly managed by the Chinese Academy of Sciences and the European Space Agency.

MESSIER will try to answer two main questions: Do large galaxies form by accreting smaller galaxies and what is the nature of the cosmic web. Although MESSIER will only carry a mirror that is 50 cm in diameter, its simple but innovative design, which has no moving parts, will help answer these questions. It will incorporate an off-axis reflector design that will not have obstructions in the field of view, yielding a precise point spread function (PDF) with virtually no tail. Because this PDF will be so precisely defined, extended low surface brightness objects can be resolved as overdensities in the observational data. It will scan the sky in drift mode with 16 CCDs, in total having 128 million pixels. He expects that MESSIER will enjoy a limiting visual magnitude of 32 and a limiting magnitude in ultraviolet of 37, exceeding the capability of ground-based facilities. In addition, he expects that three-million galaxies will be recorded over five years of operation, with many showing streams and smaller satellite galaxies. These results will give astronomers insights into the evolutionary history of galaxies and large scale structures which trace the cosmic web.

Valls-Gabaud ended the talk by mentioning that MESSIER presents opportunities for synergistic research with other projects, such as GAIA, LAMOST and in the field of time-domain astronomy. He hopes that plans for the project can be finalized by 2020, and then the satellite can be built and launched soon afterward.