HR: 1330h
AN: P12A-1047    [PDF]
TI: Io Science Opportunities From the JIMO Mission
AU: * Spencer, J R
EM: spencer@lowell.edu
AF: Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001 United States
AU: Lopes, R
EM: rlopes@isaac.jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, CA 91109 United States
AU: Smythe, W D
EM: wsmythe@lively.jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, CA 91109 United States
AB: Io is the only place beyond Earth where we can watch geological processes in action. It has much to teach us about large-scale volcanic processes in general, the history of the early Earth, which at one time may have had a heat flow approaching Io's 2 -- 3 W m$^{-2}$, and the nature of tidal heating in the Jupiter system and beyond. Though the nominal mission of the proposed Jupiter Icy Moons Orbiter (JIMO) does not include close approaches to Io, the mission can still make unique and important contributions to the understanding of Io and its active volcanism. Dynamic volcanic phenomena (e.g., active lava flows and pyroclastic events) typically evolve on timescales of hours to weeks and on spatial scales up to tens of kilometers. However, existing coverage of Io does not cover this range of spatial and temporal scales, and thus has provided very limited ability to watch volcanic activity as it happens. Galileo provided spatial resolution down to a few meters but temporal resolution no better than a few months, and Earth-based techniques provide temporal resolution down to hours or days but spatial resolution no better than $\sim$ 100 km. A 0.5 meter aperture telescope on JIMO could image Io from the distance of Ganymede with diffraction-limited resolution ranging from 1 km in the visible to 25 km at 10 $\mu$m. Io observations could be concentrated in the several-month periods of Jovicentric orbit while JIMO transfers between icy satellite orbits, causing minimal interruption to JIMO's icy satellite mapping program. If JIMO has a scan platform capable of rapid pointing, full-disk observations of Io could be taken as frequently as once per hour, for example, interleaved with observations of other targets such as Jupiter and long-range observations of the icy satellites. Io-optimized instrumentation would include the following: (i) A 0.2 -- 0.3 $\mu$m spectrograph for mapping atmospheric SO$_2$ and other species; (ii) Visible imaging in several broadband and narrowband filters from 0.35 -- 1.0 $\mu$m, for geomorphology and observations of plumes and pyroclastic deposits, and atmospheric emissions in eclipse; (iii) A 1 -- 5 $\mu$m spectrograph for both reflectance spectroscopy of surface species and measurements of the temperature and area of hot volcanic materials via their thermal emission; and (iv) thermal infrared imaging in several broadband filters from 5 -- 30 $\mu$m, for studies of lava flow cooling, surface thermal inertia, and global heat flow. With this instrumentation we could watch the complete evolution of several major eruptions on Io over the course of the JIMO mission. Science results would include, for example: (i) Magmatic temperatures during the early phases of major eruptions, providing critical constraints on magma composition and Io's interior structure; (ii) Rates of supply of gas from volcanic eruptions to Io's atmosphere, and condensed volatiles to its surface; (iii) The influence of major eruptions on Jupiter's magnetosphere, using other magnetospheric observations from JIMO; (iv) Rates of magma generation, providing constraints on volcanic "plumbing" and lava composition; (v) Accurate measurement of Io's endogenic heat flow and its spatial distribution, with implications for understanding Io's interior structure and the orbital and tidal evolution of all the Galilean satellites. While science return would be even greater if JIMO was able to approach Io closely, huge advances in our understanding of Io will be possible even from relatively distant observations, if Io science is given sufficient priority in the planning of JIMO's instrumentation and observations.
DE: 5400 PLANETOLOGY: SOLID SURFACE PLANETS
DE: 5418 Heat flow
DE: 5464 Remote sensing
DE: 5480 Volcanism (8450)
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting