Beyond Neptune II

The outer solar system beyond Neptune’s orbit is a relatively unfamiliar world to the human being, and yet it is believed to contain debris of the primordial solar disk, and therefore carries much information about the early solar system. We propose to study the trans-Neptunian objects (or Edgeworth-Kuiper Belt Objects, EKBO’s), using the stellar occultation method. We have acquired an experience and leadership in that domain, for which very few teams exist world-wide. In the last three years, we have been able to become leaders in prediction, observations and analysis of stellar occultations by distant solar system objects. We have also developed or acquired state-of-the-art fast and sensitive instruments for future campaigns. These achievements are illustrated by our successful recent observations of stellar occultations by (20000) Varuna, 2003 AZ84 and dwarf planet Eris, providing shapes, surface properties and atmospheric limits for those bodies, and breaking records as most distant solar sytem objects ever studied by stellar occultations. In parallel, we have built an innovative multi-fiber high-speed photometer (MIOSOTYS) which may discover new and exciting astrophysical phenomena. Building on this expertise, we now propose a two-fold project to pursue and amplify those achievements: One side of the project is the study of the largest EKBO’s using predicted occultations. This will allow us to (a) monitor Pluto’s (and its twin Triton’s) atmospheric seasonal variations over years, (b) improve the orbital elements of Pluto's and other EKBOs’ satellites, (c) measure sizes and shapes of several EKBO’s at sub-kilometric accuracy, thus pinning down fundamental physical parameters such as densities, albedos and rotational states, and (d) discover new EKBO’s with atmospheres. The other aspect of the project is the detection of serendipitous EKBO occultations, revealing 0.1 to 1km-sized objects during unpredicted events. This would allow us to (a) reconstruct the EKB (and possibly Oort cloud) structure from statistical studies of those occultations and (b) give the size distribution of those small bodies, an important parameter for constraining formation scenarii. We now want to develop a Fast Multi Object Photometer (UltraPhot) on the ESO Very Large Telescope « Kueyen » at Cerro Paranal, Chile, for simultaneous fast photometry of one hundred stars, in collaboration with our colleagues of the National Tsing Hua University (NTHU) in Taiwan. Key words: Astronomical Instrumentation, Optical Observations, Trans-Neptunian Objects