From spencer Tue Aug 22 12:48:13 1995
From spencer Tue Aug 22 12:48:13 1995
To: oleroemer
Subject: Io Volcano News
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Status: RO

More on Io's current active state...

I have reduced the August 19th 2.3 micron lightcurve of Io's Jupiter
occultation reappearance, that Michael Hicks and I obtained at the
Lowell 72" with OSIRIS, and have confirmed that there are *two* bright
hot spots currently active on the Jupiter-facing hemisphere.

The brightest hot spot (contributing 48% of the 2.3 micron flux) is the
same one that I noted at 3.5 microns at the IRTF on July 25, and which
was presumably responsible for the 2.1 micron brightening first seen by
Murray Silverstone at UCLA on July 20th (but not seen by Jay Goguen and
Diana Blaney at 4.8 microns on July 18th).  It has thus been active for
a full month.  It is in the northern hemisphere and is probably at the
unnamed caldera at 22 N, 351 W.

The second new hot spot contributes 30% of the total 2.3 micron flux
and is further west, near longitude zero if it's at the equator, though
we have no information on its latitude.  A very faint spot,
contributing about 8% of the total 3.5 micron flux, emerged at the
exact same relative time in our July 25 IRTF lightcurve, and is likely
to be the precursor to this spot.  The 0.3-magnitude 2.1 micron
brightening seen by Murray Silverstone between July 27 and August 12 is
of about the right magnitude to be due to the onset of this second
eruption.

The remaining 22% of the August 19 2.3 micron flux comes mostly from
two additional faint hot spots.  One is probably Loki and the other,
on the leading hemisphere, may be Kanehekili.

Including the March 23 - April 8 event that may have been at Surt, we
have now seen three major high-temperature events on the Jupiter-facing
hemisphere in 1995: at least two of these have lifetimes of several
weeks.  In my five previous years of Io monitoring I never saw any
events like these: all major brightenings that I saw on the
Jupiter-facing hemisphere before 1995 were at Loki (which has been
quiet this year).  Interesting...