TSU PRISM Seminar No. 8-7 -- 臺空人線上講座系列

400 years after Galileo pointed a telescope at celestial objects for the first time, neutral atom astronomy adds to the electromagnetic spectrum and right away reaches its horizon with the Interstellar Boundary Explorer (IBEX), launched October 19, 2008. After validation with energetic neutral atom (ENA) images of the moon, its two ENA cameras take global images of the solar system's interaction with its galactic neighborhood.
They return stunning images of the heliospheric boundary region, where the solar wind slows down in response to the surrounding interstellar medium, only penetrated thus far by the Voyager spacecraft in two directions. Unexpectedly, the ENA images show a bright and persistent "Ribbon" across the sky, serving as a compass for the local interstellar magnetic field, whose direction agrees with previous inferences, the general direction obtained from the polarization of starlight, and the observed anisotropy of TeV cosmic rays. However, the processes leading to the bright ENA emission are still under debate. Time variations in the ENA fluxes as a function of energy provide additional constraints and implicate the neutral solar wind that penetrates beyond the heliospheric boundary.
The IBEX-Lo camera catches the interstellar neutral (ISN) wind of H, He, O, and Ne atoms that blows through the solar system at a speed of ≈26 km/s. It arises from the Sun's motion relative to the very local interstellar medium (VLISM) surrounding the solar system, first identified in the Sun's ultraviolet light, followed by pickup ions in the solar wind. The observed flow distribution is an excellent probe of the VLISM. In comparison with high-resolution absorption lines from nearby stars with the Hubble Space Telescope, the recently achieved precision of the ISN velocity vector indicates that the solar system passes through an interaction region between the two closest interstellar clouds. Together, the interstellar flow and magnetic field control the size and shape of the heliosphere and the deflection of interstellar plasma around this obstacle, whose signatures are evident in the ENA images. To resolve the puzzles uncovered by the IBEX and Voyager missions, NASA has devoted to these objectives its next solar terrestrial probe, the Interstellar Mapping and Acceleration Probe (IMAP), with a planned launch in 2025.