臼井 文彦

Abstract The Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE) is a planned M-class science space mission by the Institute of Space and Astronautical Science, the Japan Aerospace Exploration Agency. JASMINE has two main science goals. One is Galactic archaeology with a Galactic Center survey, which aims to reveal the Milky Way’s central core structure and formation history from Gaia-level (∼25 ${\mu} $as) astrometry in the near-infrared (NIR) Hw band (1.0–1.6 ${\mu} $m). The other is an exoplanet survey, which aims to discover transiting Earth-like exoplanets in the habitable zone from NIR time-series photometry of M dwarfs when the Galactic Center is not accessible. We introduce the mission, review many science objectives, and present the instrument concept. JASMINE will be the first dedicated NIR astrometry space mission and provide precise astrometric information on the stars in the Galactic Center, taking advantage of the significantly lower extinction in the NIR. The precise astrometry is obtained by taking many short-exposure images. Hence, the JASMINE Galactic Center survey data will be valuable for studies of exoplanet transits, asteroseismology, variable stars, and microlensing studies, including discovery of (intermediate-mass) black holes. We highlight a swath of such potential science, and also describe synergies with other missions.

Structural, Thermal and Optical Performance (STOP) analysis is performed to investigate the stability of the telescope to be onboard the Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE). In order to perform one of the prime science objectives, high-precision astrometric observations in the wavelength range of 1.0–1.6 µm toward the Galactic center to reveal its central core structure and formation history, the JASMINE telescope is requested to be highly stable with an orbital change in the image distortion pattern being less than a few 10 µas after low-order correction. The JASMINE telescope tried to satisfy this requirement by adopting two design concepts. Firstly, the mirror and their support structures are made of extremely low coefficient-of-thermal-expansion materials. Secondly, their temperatures are highly stabilized with an orbital variation of less the 0.1 ◦C by the unique thermal control idea. Through the preliminary STOP analysis, the structural and thermal structural feasibility of the JASMINE telescope is considered. By combining the results of the structural and thermal design, its thermal deformation is estimated. The optical performance of the JASMINE telescope after the thermal deformation is numerically evaluated. It is found that the thermal displacement of the mirrors in the current structural thermal design produces a slightly large focus-length change. As far as the focus adjustment is adequately applied, the orbital variation of the image distortion pattern is suggested to become acceptable after the low-order correction.

Abstract We have conducted numerical simulations to reproduce the observed optical energy profile of the 15 October 2021 (UT) impact flash on Jupiter, which was the largest and the most well-observed flash event detected by ground-based movie observations. The observed long-duration (∼5.5 s) optical emission can be reproduced by an impact of an object with an exceptionally small angle of entry relative to the horizontal. The apparent lack of the impact debris feature despite the large impact object was possibly due to the shallower angle of entry (≤12○), which resulted in the lower ablation per unit volume at altitudes higher than 50 km, and the volume densities of the ablated materials were too low to allow the debris particulates to coagulate. The absence of temporal methane absorption change in the observed flash spectrum is consistent with the best-fit results. The model better fits the observed optical energy profile for weaker material (cometary and stony) cases than for metallic ones. Based on the simulation results, prospects for future observations of impact flashes are discussed.