4 research outputs found
Debris Field of the July 19, 2009, Impact in Jupiter and Its Long-term Evolution
A multi-platform suite of imaging and spectroscopic observations of Jupiter\u27s atmosphere tracked the evolution of the debris field of an unknown impactor on 2009 July 19. The initial debris field is similar to those of intermediate Shoemaker-Levy 9 fragments, suggesting a body hundreds of meters in size, if icy, entering from the west and slightly north. The field is detectable in the visible as dark material and in the near-IR by high-altitude particulate reflectivity; it was quickly redistributed by different zonal flows across its latitudinal range. At first, the particulate field was highly correlated with areas of enhanced temperatures and enhanced ammonia and ethane emission, but this was no longer true by mid-August. As of Sept. 2, the debris field was undetectable in the thermal, detectable in the visible with good seeing, and still prominent near 2 microns wavelength. Visibly, the impact scar consists of two dark regions along the same latitude, ostensibly different from the central bright region associated with the near-IR debris pattern. Both morphologies show eastern and western extensions propagating away from the original impact site, which appear to be influenced by flows around vortices previously undetected in Jupiter atmosphere. These observations define the flow field just north of Jupiter\u27s southern polar vortex at higher altitudes than tracked in Jupiter\u27s main cloud deck
Long-Term Evolution of the Aerosol Debris Cloud Produced by the 2009 Impact on Jupiter
We present a study of the long-term evolution of the cloud of aerosols produced in the atmosphere of Jupiter by the impact of an object on 19 July 2009 (SĂĄnchez-Lavega, A. et al. [2010]. Astrophys. J. 715, L155âL159). The work is based on images obtained during 5 months from the impact to 31 December 2009 taken in visible continuum wavelengths and from 20 July 2009 to 28 May 2010 taken in near-infrared deep hydrogenâmethane absorption bands at 2.1â2.3 ÎŒm. The impact cloud expanded zonally from âŒ5000 km (July 19) to 225,000 km (29 October, about 180° in longitude), remaining meridionally localized within a latitude band from 53.5°S to 61.5°S planetographic latitude. During the first two months after its formation the site showed heterogeneous structure with 500â1000 km sized embedded spots. Later the reflectivity of the debris field became more homogeneous due to clump mergers. The cloud was mainly dispersed in longitude by the dominant zonal winds and their meridional shear, during the initial stages, localized motions may have been induced by thermal perturbation caused by the impactâs energy deposition. The tracking of individual spots within the impact cloud shows that the westward jet at 56.5°S latitude increases its eastward velocity with altitude above the tropopause by 5â10 m sâ1. The corresponding vertical wind shear is low, about 1 m sâ1 per scale height in agreement with previous thermal wind estimations. We found evidence for discrete localized meridional motions with speeds of 1â2 m sâ1. Two numerical models are used to simulate the observed cloud dispersion. One is a pure advection of the aerosols by the winds and their shears. The other uses the EPIC code, a nonlinear calculation of the evolution of the potential vorticity field generated by a heat pulse that simulates the impact. Both models reproduce the observed global structure of the cloud and the dominant zonal dispersion of the aerosols, but not the details of the cloud morphology. The reflectivity of the impact cloud decreased exponentially with a characteristic timescale of 15 days; we can explain this behavior with a radiative transfer model of the cloud optical depth coupled to an advection model of the cloud dispersion by the wind shears. The expected sedimentation time in the stratosphere (altitude levels 5â100 mbar) for the small aerosol particles forming the cloud is 45â200 days, thus aerosols were removed vertically over the long term following their zonal dispersion. No evidence of the cloud was detected 10 months after the impact