(IAAC) Upcoming Research Observing Opportunity
Observation Opportunity Toward Analysis of the Atmosphere of Io
It would seem that no one has ever predicted any mutual eclipses
of the Four Great Moons of Jupiter. Discovering this, I attacked
this immensely complex problem in 1996. After several months of
calculations, computer processing, and cross-checking, I came up
with a series of predictions. A group of events will occur during
1997, with the next such series late in 2002.
Quite a few occultations are predicted, most of which are partial
events. A lesser number of eclipses are predicted, 23 of which are
total or annular. (of the 1997 series)
Of these, two are events where Io blocks the Sun's light from
Europa. These two events, predicted for 4/12 and 4/16, are
unique in allowing potential analysis of any atmosphere Io may have.
A fraction of a second before totality, the only light which could
get to Europa had to pass within a few miles of Io's surface, on
its way from the Sun. If Io has an atmosphere (sulfurous, perhaps?),
additional absorbtion lines should appear in the spectrum of light
impinging on Europa's surface. This spectrum could then be compared
with a standard spectrum of the light reflected off Europa to
discover these differences, which imply gases in Io's atmosphere.
If a rapid series of spectra were taken as totality approached, it
may be possible to identify the vertical distribution of components
of Io's atmosphere.
As mentioned above, there are only two of these opportunities available
prior to Dec 2002. The first, on Apr 12, will only be viewable from
parts of Russia and the Mid-east (about 85řE long. to 50řE long.) The
time of this event is JD 2450551.4384. The second event will
only be viewable just before astronomical dawn along the
west coast of the U.S. on Apr 16. (time JD 2450554.9847)
In both cases, both moons are West of the planet, Io about 1.6
radii away and Europa about 4.3 Jupiter radii from the center of
It is my hope that some of the equipment available in west coast
observatories might be done with their night's work due to the
impending dawn's light. If so, please direct a telescope with a
spectrograph at Europa. The event is rather brief. Totality is
predicted at about 17 seconds, with the entire eclipse phenomenon
being completed in about 4 minutes. There is a slight chance that
a 1% sliver of the North edge of Europa may not be eclipsed. This
should not materially affect the experiment described above.
The other 21 total or annular mutual eclipses involve various
combinations of the four moons. These occur later this spring and
summer. Several would allow similar analysis of the atmospheres
of Ganymede and Callisto.
If nothing else, it seems that it would be memorable to even just
visually observe such a rare event. A few historical references
exist where an astronomer was observing Jupiter and one of its
moons briefly 'blinked out', but no one has EVER observed a
predicted example of it.
If the differential spectrum concept develops useful results, a
careful study of Saturn's system would be appropriate to predict
when Titan might eclipse one of the other moons, thereby disclosing
its atmosphere's constitution. In addition, rapid sequence spectra
of Jupiter's moons being eclipsed by the planet might give upper
atmosphere details of Jupiter.
A full list of the 450 partial and total occultations and eclipses
of the 1997 series is available on request.
There are some really odd events in this series. On May 2, Io will
appear to be substantially East of Jupiter while Callisto is ever
further West of the planet. An annular event will occur where Io
will eclipse Callisto. During the annular 'totality', Callisto will
go into Jupiter's shadow. The combined shadow pattern should be
REALLY peculiar looking!
Finally, regarding Io again, a significant partial eclipse is predicted
for the morning of April 9, visible in the Mid-west and West coast of
the United States. The time is JD 2450547.8921, which is near
astronomical dawn for the Midwest. A sliver of the South edge of Europa
should remain lit by the Sun, about 7% of Europa's diameter. This
should cause Europa to drop about 4 magnitudes in brightness for
about 20 seconds.
BA Physics, University of Chicago
PO Box 93
Thornton, IL 60476