[meteorite-list] Remnants of the 1994 Comet Crash in Jupiter

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Sep 13 17:43:49 2004
Message-ID: <200409132143.OAA08659_at_zagami.jpl.nasa.gov>

Observatoire de Paris
Paris, France

Contact:
Bruno B?zard, Observatoire de Paris, LESIA
T?l: 33 1 45 07 77 17
Fax: 33 1 45 34 76 83
E-mail: Bruno.B?ZARD_at_obspm.fr

Emmanuel Lellouch, Observatoire de Paris, LESIA
T?l: 33 1 45 07 76 72
Fax: 33 1 45 07 71 10
E-mail: Emmanuel.LELLOUCH_at_obspm.fr

3 September 2004

Remnants of the 1994 comet crash in Jupiter

In July 1994, more than 20 fragments of Comet Shoemaker-Levy struck Jupiter at a
latitude of about 45 deg S (see Figure 1). High-temperature chemical reactions
that occurred during the impacts created a suite of new compounds, such as
hydrogen cyanide (HCN) and carbon monoxide (CO). The comet also deposited water
vapor, which in presence of CO and sunlight is expected to be converted
gradually into carbon dioxide (CO2). Since the collision, these species have
been slowly spread in latitude but are still visible ten years later. A study to
which were associated researchers from Paris Observatory, and published in the
online version of the journal Science, shows that unexpectedly the latitudinal
distributions of HCN and CO2 are markedly different (Fig. 2). This result,
derived from measurements by the Cassini spacecraft as it encountered Jupiter in
December 2000, is presently difficult to understand.

The Cassini spacecraft, now orbiting Saturn, swung by Jupiter in December 2000.
The infrared spectrometer CIRS observed the planet in the spectral range 10 -
1400 cm-1 (7 mm - 1 mm) at a spectral resolution up to 0.5 cm-1 and a spatial
resolution of 0.02 of the planetary diameter at closest approach. The data
collected during the encounter allowed mapping the abundances of HCN and CO2 in
the Jovian stratosphere (Kunde et al. 2004).

HCN peaks near the impact latitude (45 deg S) and has a broad distribution (see
Figure 2). It decreases smoothly toward the north up to approximately 50 deg N.
Beyond 50 deg N or S, the abundance falls off abruptly. Once produced by shock
chemistry during the SL9 impacts, HCN is stable, so that it is a tracer of
atmospheric motions. The location of peak abundance still being around the
impact latitude indicates that equatorial spreading occurred mostly by
wave-induced diffusion rather than meridional winds. The decrease at high
latitudes could result from strong circumpolar winds (vortices), which
dynamically isolate polar regions from lower latitudes. This effect is analogous
to the polar vortex that produces a confinement vessel for the Antarctic ozone
hole in Earth's stratosphere.

In this framework, the distribution of CO2 is quite surprising, with a maximum
concentration southward of 60 deg S, three times higher than at the impact
latitude. It decreases abruptly northward of 50 deg S and is only marginally
detected northward of 30 deg S. If, as admitted up to now, HCN and CO2 are both
products of the SL9 collision (Griffith et al. 2004; Lellouch et al. 2002) and
are similarly distributed in altitude, this is extremely surprising and
difficult to understand.

Perhaps the two species got distributed at different altitudes and are therefore
transported by different atmospheric currents. An alternative interpretation is
that some non-SL9 or post SL9 chemistry is involved. Maybe the formation of
carbon dioxide is more complex than we thought. In fact, the precipitation of
oxygen ions from the Jovian magnetosphere in the auroral regions may lead to the
formation of water vapor and OH radicals. These radicals could then react with
the CO from SL9 and form, at high southern latitudes, the CO2 observed by
Cassini/CIRS. It not clear however if the oxygen influx required to reproduce
the observations is consistent or not with the loading rate of the magnetosphere
from the Galilean satellites (mostly Io).

These observations clearly give valuable insights into the dynamics and
chemistry of the upper atmosphere of Jupiter. We still need to work on the
above, or perhaps others, scenarios to really understand what the observations mean!

References

Kunde, V.G., Flasar, F.M., Jennings, D.E., B?zard, B., Strobel, D.F. et al.
2004. Jupiter's atmospheric composition from the Cassini thermal infrared
spectroscopy experiment. ? para?tre dans Science (10 septembre 2004). Online
version accessible at http://www.sciencexpress.org (19 august 2004)

Griffith, C.A., B?zard, B., Greathouse, T., Lellouch, E., Lacy, J., Kelly, D.,
Richter, M.J. 2004. Meridional transport of HCN from SL9 impacts on Jupiter.
Icarus 170, 58-69

Lellouch, E., B?zard, B., Moses, J.I., Drossart, P., Feuchtgruber, H., Bergin,
E.A., Moreno, R., Encrenaz, T. 2002. The origin of water vapor and carbon
dioxide in Jupiter's stratosphere. Icarus 159, 112-131

Several co-investigators from LESIA are participating to the analysis of the
CIRS data.

IMAGE CAPTIONS:

[Figure 1:
http://www.obspm.fr/actual/nouvelle/sep04/jupiter-f1.jpg (44KB)]
In July 1994, more than 20 fragments of Comet Shoemaker-Levy 9 (SL9) collided
with Jupiter. New gas compounds, produced through shock chemistry along with
dark solid particles, were then deposited in the stratosphere. Some species,
such as HCN and CO2, are still detectable today. [Credit NASA/Hubble Space
Telescope Comet Science Team].

[Figure 2:
http://www.obspm.fr/actual/nouvelle/sep04/jupiter-f2.gif (23KB)]
Latitudinal distribution of HCN and CO2 as determined from measurements by the
CIRS instrument aboard Cassini in December 2000. The plotted intensities are
proportional to the column abundance of the species. The original source of
these two compounds is thought to be the SL9 impact in 1994, around 45 deg S.
The differences in their latitudinal variations are thus unexpected and not
clearly understood.
Received on Mon 13 Sep 2004 05:43:46 PM PDT