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sl9-jpl.09
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9. What Do Scientists Expect to Learn from All of This?
To give a simple and succinct answer to the title of
this section, scientists hope to learn more about comets, more
about Jupiter, and more about the physics of high velocity impacts
into a planetary atmosphere. Something has already been learned
about comets from the behavior of Shoemaker-Levy 9 during its
breakup, as discussed in Section 4. Bits and pieces of what
everyone hopes will be learned have been noted in Sections 5
through 8. A more complete summary follows.
If the fragments explode above the clouds, there should be enough
light reflected from various Jovian satellites to take spectra of
the explosions. Since the atmosphere of Jupiter contains very few
heavier elements to contaminate the spectra, they could give a
great deal of information about the composition of cometary
solids. If the fragments explode below the clouds, then
spectroscopy must wait until the impact sites rotate into view
from Earth. By that time everything will have cooled a great deal,
and the cometary component will have been diluted by mixing with
the Jovian atmosphere, making such study difficult. In that case
the Jovian material itself may prove of interest, with
spectroscopic study giving new knowledge of Jupiter's deeper
atmospheric composition.
It seems somewhat more certain that new knowledge of Jupiter's
atmosphere will be obtained, even if predictions differ as to
exactly what that new knowledge will be. There is nearly unanimous
agreement that the impacts will cause observable changes in
Jupiter, at least locally at the impact sites. These may include
changes in the visible appearance of the clouds, locally or more
widely, measurable temperature fluctuations, again locally or more
widely, composition changes caused by material brought up from
below the clouds (if the fragments penetrate that deeply), and/or
chemical reactions brought about by the thermal pulse and the
introduction of cometary material. Any dynamic processes such as
these will give a new and better understanding of the structure of
Jupiter's atmosphere, perhaps of its motion as well as its static
structure.
If sufficient material impacts Jupiter's rings or especially the
ring satellites, then there should be local brightening caused by
the increase in reflecting area due to the introduction of new
material. These new ring particles will each take up their own
orbits around Jupiter, gradually spreading out and causing local
brightening followed by slow fading into the general ring
background. Careful mapping of that brightening and fading will
reveal a great deal about the structure and dynamics of the rings.
Many believe that impacts on those small inner satellites are the
source of the rings, the reason or their existence. Enhancement
of the rings from Shoemaker-Levy 9 impacts would be strong
confirmation of this idea. Similarly, the interaction of cometary
dust with the magnetosphere and with the Io torus will be quite
informative, if the dust density proves sufficient to cause
observable effects. Radio telescopes will be active in the
magnetospheric studies, along with optical spectroscopy of the
ions and atoms in the torus.
Last, but far from least, the physics of the impact phenomena
themselves, determined from the reflected light curves and from
spectra, will be most instructive. Note the inability of
scientists to agree on the level of Jupiter's atmosphere at which
the terminal explosion will occur. (A few even believe that there
will be no terminal explosion or that it will occur so deep in
that atmosphere as to be completely unobservable.) Entry phenomena
on this scale cannot be reproduced, even by nuclear fusion
explosions, and have never before been observed. Better knowledge
of the phenomena may allow scientists to predict more accurately
just how serious could be the results of future impacts of
various-sized bodies on Earth, as well as to determine their
effects in the past as registered by the fossil record.