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| Titel |
Spectroscopic Evidence for the Asteroidal Nature of the July 2009 Jovian Impactor |
| VerfasserIn |
Carey Lisse, Glenn Orton, Padma Yanamandra-Fisher, Leigh Fletcher, Imke de Pater, Heidi Hammel |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042419
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| Zusammenfassung |
| The collision of a large object with Jupiter on July 19, 2009, heated its atmosphere, modified
its composition and generated a prominent field of deposited particulate debris.
Low-resolution 7-24 μm spectroscopy of the impact field obtained using the T-ReCS
mid-infrared camera/spectrometer on Gemini/South on 24 July 2009 has revealed an excess
9-μm absorption in the impact debris in addition to that supplied by hot ammonia created in
the impact.
We have searched for candidate materials that would best fit the spectral feature near 9
μm, and find that the feature cannot be matched with candidate materials in Jupiter’s
atmosphere. A search through a large suite of gaseous and solid absorption spectra (c.f Lisse
et al. 2008, 2009) revealed that the major competent matches were for (a) obsidian, a glassy
silica, and (b) quartz and cristobalite, crystalline silicas, kinetic alteration products of
primitive body ferromagnesian silicates formed at high pressures and temperatures over 1500
K. There are also weak features at 10 – 11 um consistent with olivine absorptions. While the
high temperatures required to create silicas are also high enough to destroy the non-refractory
water and organics dominating icy cometary bodies, and thus destroy their spectral signal,
there was no detectable absorption due to pyroxene materials, which, along with
olivines in roughly equal measure, comprise the majority of refractory silicaceous
species found in comets (Lisse et al. 2007). This suggests that the impacting body
was not a comet, but an olivine-rich differentiated body similar to asteroids that
are abundant in the outer regions of the main asteroid belt (Lodders and Fegley
1998). We speculate that the weak structural strength of bulk cometary material
causes a comet impactor to catastrophically disrupt at higher altitudes and lower
temperatures than a strong, dense asteroidal body, so that the cometary refractory dust
component remains relatively cold and unaltered through blowback and Jovian surface
deposition, while asteroidal dust is heated enough to be transformed from silicates to
silicas.
Ancillary evidence for the asteroidal nature of the impactor arises from the singular
nature of the impact site, the existence of asteroidal orbits consistent with the observed
geometry (Chodas 2009, Orton et al. 2010), and the differences between the observed 2009
opacity spectra of the debris and the observed debris opacity created in July 1994 by the SL9
fragments. Nicholson et al. (1995) noted the presence of a non-gaseous component of their
spectrum of the SL9 R fragment impact, which they fit with the “astronomical silicate” of
Draine (1985). Griffith et al. (1997) also required an opacity source besides NH3 gas in order
to explain the spectral continuum associated with debris from the L fragment, inferring that it
was most likely the result of a silicate feature similar to those in comets (Hanner
et al. 1994). Both of these are consistent with increased opacity in the 10-12 μm
region due to a mix of stratospheric debris consisting of olivines and pyroxenes,
typically found in comets, without any additional opacity at ~9 um due to silica. |
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