Mysterious Light Emitted During Lunar Eclipse of Galilean Satellites Observations Using the Subaru Telescope and Hubble Space Telescope

Research Press Release | June 30, 2014

Press Release
Key Points * Observations using Japan’s Subaru Telescope and others have discovered a faint light from Galilean satellites while in the Jovian shadow.

* The phenomenon is thought to be due to sunlight passing through the Jovian atmosphere.

* The discovery is expected to provide a new key to understanding the atmosphere of planets, including those beyond the solar system.

Overview Observations with the Subaru Telescope and the Hubble Space Telescope have revealed a phenomenon in which the Galilean satellites (the four moons of Jupiter – the innermost being Io, followed by Europa, Ganymede, and Callisto in that order) entering the shadow of Jupiter shine faintly (at one-millionth of normal light levels) despite being in a state of lunar eclipse and not directly illuminated by the sun (see diagram). The phenomenon is not clearly understood, however in the opinion of the research team, it is due to sunlight scattered by mist in Jupiter’s upper atmosphere indirectly illuminating the Galilean satellites. A similar phenomenon is observed when our moon appears red when completely hidden in the earth’s shadow in a total eclipse. Investigation will continue in an effort to understand the nature of the Jovian mist, hitherto very difficult to observe, and to facilitate a new understanding of the atmosphere of the many planets discovered beyond our solar system in recent years.

Hokkaido University research personnel contributed to the current discovery through observations with the Subaru Telescope.

Reference – National Astronomical Observatory of Japan, Subaru Telescope Site


Kiyoshi Kuramoto, Professor, Graduate School of Science, Hokkaido University

TEL: +81-11-706-3827

FAX: +81-11-706-2760



ガリレオ衛星が「月食」中に謎の発光? すばる望遠鏡とハッブル宇宙望遠鏡で観測

Publications  The Astrophysical Journal (2014.7.10)