11:45 AM - 12:00 PM
[PPS01-10] Feasibility study of UV observation of water vapor plumes on icy moons for LAPYUTA mission considering influence of Geococona
Keywords:Icy moon, Europa, UV
Inside Jupiter's moon Europa, Ganymede, and Saturn's moon Enceladus, putative oceans under the ice shell could be sustained. In the previous study of Roth et al (2014), Hubble Space Telescope observed the enhancement of HI 121.6 nm and OI 130.4 nm emissions in the limb near the Europa south pole. They considered the electron impact of H2O in the plume yields HI and OI emissions. Geological conditions of ejecting gas and dust form Europa plumes are not understood because there are very few observations which succeed to detect Europa plume signatures. Although the water vapor in the plumes do not necessarily pass through the underground ocean, it may include important information to consider the habitable environment of the icy moons.
LAPYUTA (Life-environmentology, Astronomy, and PlanetarY Ultraviolet Telescope Assembly) is the future Earth-orbiting UV telescope project. Using past HST observations and the above model as a reference, we estimated the intensity distributions of the Europa plume, the atmosphere, and the reflected light. And we verified how much the presence of the geocorona around the satellite is acceptable for the signal-to-noise ratio to exceed 3 with an integration time of 10 hours. When the spatial resolution of the space telescope was about 0.1", we found that the plume could be discriminated in the observed two-dimensional distribution if the intensity of the HI 121.6 nm emission of the average geocorona was about 6,000-8,000 Raylighs. Next, satellite orbits with a perigee altitude of 500 km and an apogee altitude of 10,000 km, where the above conditions are expected to be achievable, are assumed. We created several models of the intensity of geocoronal emissions that take into account the satellite orbit, the direction of the line of sight, and the shadow of the Earth. The model shows that the satellite can observe Europa for about 150 minutes out of a orbiting period of 220 minutes. This indicates that if the satellite continuously observes Europa during its four orbits of the Earth, it can achieve an integration time of 10 hours.
LAPYUTA (Life-environmentology, Astronomy, and PlanetarY Ultraviolet Telescope Assembly) is the future Earth-orbiting UV telescope project. Using past HST observations and the above model as a reference, we estimated the intensity distributions of the Europa plume, the atmosphere, and the reflected light. And we verified how much the presence of the geocorona around the satellite is acceptable for the signal-to-noise ratio to exceed 3 with an integration time of 10 hours. When the spatial resolution of the space telescope was about 0.1", we found that the plume could be discriminated in the observed two-dimensional distribution if the intensity of the HI 121.6 nm emission of the average geocorona was about 6,000-8,000 Raylighs. Next, satellite orbits with a perigee altitude of 500 km and an apogee altitude of 10,000 km, where the above conditions are expected to be achievable, are assumed. We created several models of the intensity of geocoronal emissions that take into account the satellite orbit, the direction of the line of sight, and the shadow of the Earth. The model shows that the satellite can observe Europa for about 150 minutes out of a orbiting period of 220 minutes. This indicates that if the satellite continuously observes Europa during its four orbits of the Earth, it can achieve an integration time of 10 hours.