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McEwen Active Volcanism on Io Science 297, 2220-2221,2002.: McEwen Active Volcanism on Io Science 297, 2220-2221,2002. 今週の科学2002.10.4
Facts on Io: Facts on Io Jupiter’s Moon found in 1610 by Galileo Galilei Diameter: 3630km
Mass(Earth=1): 0.015
Gravity(Earth=1): 0.183
Density: 3.57g/cm3
Orbital period: 1.77day
Rotational period: 1.77day
From Jupiter: 421,600km
Voyager1 Expedition in 1979: Voyager1 Expedition in 1979 volcanoes
rugged mountains
colorful surface rich in sulfurous materials
giant plumes of gas and dust Nature of the volcanism
sulfur volcanism burying a silicate subcrust
or
silicate volcanism and crust with thin sulfurous coating ~700K 1300-1450K
(earth’s basaltic lava)
Galileo Expedition from 1989-: Galileo Expedition from 1989- First Io flyby in 1995 delay of launch failure in expansion of high-gain antenna tape recorder anomaly
NO DATA Six flybys 1999-2002 some detectors were dead
or degraded on NIMS Solid State Imaging (SSI)
Near-Infrared Mapping Spectometer(NIMS)
Galileo Image of Io: Galileo Image of Io
distant Galileo observations 1996-1998: distant Galileo observations 1996-1998 found 41 hotspots
above ~1000K
all in the dark patches
Six close Io flybys 1999-2002: Six close Io flybys 1999-2002 hot silicate sulfur dioxide frost 150-300 major hotspots
- lava flows
- lava lakes
-caldera-like depressions
Dramatic eruption at Pillan Patera in 1997: Dramatic eruption at Pillan Patera in 1997 4 April 1997 19 September 1997 400km lava flows
(Arizona-size)
120km high plume
High temperature
~1800K
High temperature volcanism: High temperature volcanism High temperature > 1500K Today’s Earth basaltic eruption: 1300-1450K Hottest terrestrial lava at 1700-1900K are ancient (age>2000my) The study of Io may thus provide important clues
to understanding the early Earth
Mg rich volcanism: Mg rich volcanism The ancien high-temperature lavas on earth are rich in Mg Spectral data shows absorption band at ~900nm in dark patches
= orthopyroxene spectra Io is an ultramafilc world? The idea seems at odds with mantle segregation…… Keszthelyi et al. (1999)
Io’s lower mantle could be a crystal-rich magma ocean
upper mantle would consists of orthopyroxene-rich magma
overlying crust is about the same density of upper mantle
hot mantle suppress convection in Io’s core - no magnetic field difficult to explain how Io first got into that state
Galileo Today: Galileo Today 32 days to Amalthea flyby Largest of Jupiter’s smaller moons
- 270*170*150km
- irregular “potato” shape
Orbit inside the orbit of Io
-Only 2.5 Jupiter radi
Reddest object in the solar system