Аннотация
Galileo's Near-Infrared Mapping Spectrometer (NIMS) obtained its final
observations of Io during the spacecraft's fly-bys in August (131)
and October 2001 (132). We present a summary of the observations
and results from these last two fly-bys, focusing on the distribution
of thermal emission from Io's many volcanic regions that give insights
into the eruption styles of individual hot spots. We include a compilation
of hot spot data obtained from Galileo, Voyager, and ground-based
observations. At least 152 active volcanic centers are now known
on Io, 104 of which were discovered or confirmed by Galileo observations,
including 23 from the 131 and 132 Io fly-by observations presented
here. We modify the classification scheme of Keszthelyi et al. (2001,
J. Geophys. Res. 106 (E12) 33 025-33 052) of Io eruption styles to
include three primary types: promethean (lava flow fields emplaced
as compound pahoehoe flows with small plumes < 200 km high originating
from flow fronts), pillanian (violent eruptions generally accompanied
by large outbursts, > 200 km high plumes and rapidly-emplaced flow
fields), and a new style we call "lokian" that includes all eruptions
confined within paterae with or without associated plume eruptions).
Thermal maps of active paterae from NIMS data reveal hot edges that
are characteristic of lava lakes. Comparisons with terrestrial analogs
show that Io's lava lakes have thermal properties consistent with
relatively inactive lava lakes. The majority of activity on Io, based
on locations and longevity of hot spots, appears to be of this third
type. This finding has implications for how Io is being resurfaced
as our results imply that eruptions of lava are predominantly confined
within paterae, thus making it unlikely that resurfacing is done
primarily by extensive lava flows. Our conclusion is consistent with
the findings of Geissler et al. (2004, Icarus, this issue) that plume
eruptions and deposits, rather than the eruption of copious amounts
of effusive lavas, are responsible for Io's high resurfacing rates.
The origin and longevity of islands within ionian lava lakes remains
enigmatic. (C) 2003 Elsevier Inc. All rights reserved.
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