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Sanchez-Lavega A.,University of the Basque Country | Wesley A.,Acquerra Pty. Ltd. | Orton G.,Jet Propulsion Laboratory | Hueso R.,University of the Basque Country | And 12 more authors.
Astrophysical Journal Letters | Year: 2010

On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55°S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory in the opposite direction and with a lower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4800km east-west and 2500km north-south, with those produced by the SL9 fragments and dynamical calculations of pre-impact orbit indicates that the impactor was most probably an icy body with a size of 0.5-1km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890nm and K (2.03-2.36 μm) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary clouds. © 2010 The American Astronomical Society. All rights reserved.

Hueso R.,University of the Basque Country | Perez-Hoyos S.,University of the Basque Country | Sanchez-Lavega A.,University of the Basque Country | Wesley A.,Acquerra Pty. Ltd. | And 20 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Regular observations of Jupiter by a large number of amateur astronomers have resulted in the serendipitous discovery of short bright flashes in its atmosphere, which have been proposed as being caused by impacts of small objects. Three flashes were detected: one on June 3, 2010, one on August 20, 2010, and one on September 10, 2012. Aims. We show that the flashes are caused by impacting objects that we characterize in terms of their size, and we study the flux of small impacts on Jupiter. Methods. We measured the light curves of these atmospheric airbursts to extract their luminous energy and computed the masses and sizes of the objects. We ran simulations of impacts and compared them with the light curves. We analyzed the statistical significance of these events in the large pool of Jupiter observations. Results. All three objects are in the 5-20 m size category depending on their density, and they released energy comparable to the recent Chelyabinsk airburst. Model simulations approximately agree with the interpretation of the limited observations. Biases in observations of Jupiter suggest a rate of 12-60 similar impacts per year and we provide software tools for amateurs to examine the faint signature of impacts in their data to increase the number of detected collisions. Conclusions. The impact rate agrees with dynamical models of comets. More massive objects (a few 100 m) should impact with Jupiter every few years leaving atmospheric dark debris features that could be detectable about once per decade. © ESO, 2013.

Orton G.S.,Jet Propulsion Laboratory | Fletcher L.N.,University of Oxford | Lisse C.M.,Johns Hopkins University | Chodas P.W.,Jet Propulsion Laboratory | And 24 more authors.
Icarus | Year: 2011

Near-infrared and mid-infrared observations of the site of the 2009 July 19 impact of an unknown object with Jupiter were obtained within days of the event. The observations were used to assess the properties of a particulate debris field, elevated temperatures, and the extent of ammonia gas redistributed from the troposphere into Jupiter's stratosphere. The impact strongly influenced the atmosphere in a central region, as well as having weaker effects in a separate field to its west, similar to the Comet Shoemaker-Levy 9 (SL9) impact sites in 1994. Temperatures were elevated by as much as 6K at pressures of about 50-70mbar in Jupiter's lower stratosphere near the center of the impact site, but no changes above the noise level (1K) were observed in the upper stratosphere at atmospheric pressures less than ∼1mbar. The impact transported at least ∼2×1015g of gas from the troposphere to the stratosphere, an amount less than derived for the SL9 C fragment impact. From thermal heating and mass-transport considerations, the diameter of the impactor was roughly in the range of 200-500m, assuming a mean density of 2.5g/cm3. Models with temperature perturbations and ammonia redistribution alone are unable to fit the observed thermal emission; non-gray emission from particulate emission is needed. Mid-infrared spectroscopy of material delivered by the impacting body implies that, in addition to a silicate component, it contains a strong signature that is consistent with silica, distinguishing it from SL9, which contained no evidence for silica. Because no comet has a significant abundance of silica, this result is more consistent with a " rocky" or " asteroidal" origin for the impactor than an " icy" or " cometary" one. This is surprising because the only objects generally considered likely to collide with Jupiter and its satellites are Jupiter-Family Comets, whose populations appear to be orders of magnitude larger than the Jupiter-encountering asteroids. Nonetheless, our conclusion that there is good evidence for at least a major asteroidal component of the impactor composition is also consistent both with constraints on the geometry of the impactor and with results of contemporaneous Hubble Space Telescope observations. If the impact was not simply a statistical fluke, then our conclusion that the impactor contained more rocky material than was the case for the desiccated Comet SL9 implies a larger population of Jupiter-crossing asteroidal bodies than previously estimated, an asteroidal component within the Jupiter-Family Comet population, or compositional differentiation within these bodies. © 2010 Elsevier Inc.

Hueso R.,University of the Basque Country | Wesley A.,Acquerra Pty. Ltd. | Go C.,University of San Carlos | Perez-Hoyos S.,University of the Basque Country | And 13 more authors.
Astrophysical Journal Letters | Year: 2010

Cosmic collisions on planets cause detectable optical flashes that range from terrestrial shooting stars to bright fireballs. On 2010 June 3 a bolide in Jupiter's atmosphere was simultaneously observed from the Earth by two amateur astronomers observing Jupiter in red and blue wavelengths. The bolide appeared as a flash of 2 s duration in video recording data of the planet. The analysis of the light curve of the observations results in an estimated energy of the impact of (0.9-4.0) × 1015 J which corresponds to a colliding body of 8-13 m diameter assuming a mean density of 2 g cm-3. Images acquired a few days later by the Hubble Space Telescope and other large groundbased facilities did not show any signature of aerosol debris, temperature, or chemical composition anomaly, confirming that the body was small and destroyed in Jupiter's upper atmosphere. Several collisions of this size may happen on Jupiter on a yearly basis. A systematic study of the impact rate and size of these bolides can enable an empirical determination of the flux of meteoroids in Jupiter with implications for the populations of small bodies in the outer solar system and may allow a better quantification of the threat of impacting bodies to Earth. The serendipitous recording of this optical flash opens a new window in the observation of Jupiter with small telescopes. © 2010 The American Astronomical Society. All rights reserved.

Sanchez-Lavega A.,University of the Basque Country | Orton G.S.,Jet Propulsion Laboratory | Hueso R.,University of the Basque Country | Perez-Hoyos S.,University of the Basque Country | And 46 more authors.
Icarus | Year: 2011

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 (Sánchez-Lavega, A. et al. [2010]. Astrophys. J. 715, L155-L159). The work is based on images obtained during 5months 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 hydrogen-methane absorption bands at 2.1-2.3μm. The impact cloud expanded zonally from ∼5000km (July 19) to 225,000km (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 500-1000km 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 impact's 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 5-10ms-1. The corresponding vertical wind shear is low, about 1ms-1 per scale height in agreement with previous thermal wind estimations. We found evidence for discrete localized meridional motions with speeds of 1-2ms-1. 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 5-100mbar) for the small aerosol particles forming the cloud is 45-200days, thus aerosols were removed vertically over the long term following their zonal dispersion. No evidence of the cloud was detected 10months after the impact. © 2011 Elsevier Inc.

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