Effect of the Collision of Comet Shoemaker-Levy 9 on the Appearance of Jupiter in the IR
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Tidal Disruption and the Appearance of Periodic Comet Shoemaker-Levy 9
A unified model is presented that quantitatively interprets the observed characteristics of the nuclear train, the two dust trails, and the tail region of P/Shoemaker-Levy 9 in terms of a collisionally modified rotation velocity distribution of the comet's debris.
comets↗
(abstract) Cometary Particles as a Tracer of Jupiter's Stratospheric Circulation
The impact of fragments of comet Shoemaker-Levy 9 on Jupiter's atmosphere in July 1994 may provide an unprecedented opportunity to study Jupiter's stratospheric circulation. Recent calculations by Z. Sekanina predict that much of the comet material will be deposited in Jupiter's stratosphere. If so, and if the material is deposited in a confined region (10 000 km or less, horizontally) we can expect a situation analogous to an El Chichon or Pinatubo event for the terrestrial stratosphere. Initially the volatile material will be vaporized and will rapidly recondense. The large ice crystals and dust particles will rain out and be lost to the troposphere. The cloud of small particles which remain may have settling times of more than a year. These submicron to micron particles would probably be easily seen in methane filter images in the near-IR, and possibly in the ultraviolet. An observational program to monitor the dispersal of this cloud or clouds would reveal much about the nature of the circulation. Some predictions about the meridional evolution of the clouds can be made already, based on the meridional circulation model of West et al. unless the impact itself significantly disrupts the annual average circulation well after the initial transients die away.
comet Shoemaker-Levy 9 impact Jupiter stratosphere↗
Observations of comets with the IUE
Comet Shoemaker-Levey was observed on several dates in June and July 1992. Comparison of the relative brightness of a given emission between IUE and the Hubble Space Telescope (HST) Faint Object Spectrograph apertures provides information about the spatial distribution of the emitting species from which the excitation mechanisms can be inferred. The comparison between the HST and IUE spectra was abetted by the fact that comet Shoemaker-Levy did not show any indication of short-term temporal variability. Comet Swift-Tuttle is a moderately bright periodic comet that shows relatively strong temporal variations on a scale of hours and days. IUE observations of this comet were made in November 1992 and the detected variability was reported on IAU circular 5663. Coordinated ground-based observations led to the first detection of the CI(lambda)9850 transition that complements CI(lambda)1931 observed by the IUE short wavelength spectrograph and provides a means of indirectly determining the CO abundance.
Feldman, Paul D.↗
Aeronautics and Space Reports Number 267: Comet Impacts Jupiter
This video contains three different segments of computer generated simulations of the impact of comet Shoemaker-Levy 9 with Jupiter that will take place in July 1994. It includes interviews with Shoemaker and Levy, discussing pictures taken at Palomar Observatory, the comet's approach to Jupiter, fragment size, and the affects of the comet's impact on Jupiter and its atmosphere. The impact will be viewed by the Galileo spacecraft.
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Comet Impact Tape 1
Continued press coverage of the comet Shoemaker-Levy 9 impact on the surface of Jupiter is presented. This tape covers 16 Jul. 1994.
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Comet Impact Tape 2
Continued press coverage of the comet Shoemaker-Levy 9 impact on the surface of Jupiter is presented. This tape covers 16 Jul. 1994.
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Comet Impact Tape 4
Continued press coverage of the comet Shoemaker-Levy 9 impact on the surface of Jupiter is presented. This tape covers 18 Jul. 1994.
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Comet Impact Tape 5
Continued press coverage of the comet Shoemaker-Levy 9 impact on the surface of Jupiter is presented. This tape covers 19 Jul. 1994.
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Comet Impact Tape 6
Continued press coverage of the comet Shoemaker-Levy 9 impact on the surface of Jupiter is presented. This tape covers 20 Jul. 1994.
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Comet Impact Tape 8
Continued press coverage of the comet Shoemaker-Levy 9 impact on the surface of Jupiter is presented. This tape covers 22 Jul. 1994.
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Comet Impact Tape 9
Continued press coverage of the comet Shoemaker-Levy 9 impact on the surface of Jupiter is presented. This tape covers 23 Jul. 1994.
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Comet Impact Tape 3
Continued press coverage of the comet Shoemaker-Levy 9 impact on the surface of Jupiter is presented. This tape covers 17 Jul. 1994.
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Explosions of infalling comets in Jupiter's atmosphere
In view of the expected collision of comet Shoemaker-Levy 9 (1993e) with Jupiter in 1994 July, we calculate basic properties of the initial interaction for a simplified Jovian atmosphere. The comet is expected to impact Jupiter at 60 km/sec and at an angle of 45 deg to the zenith. The shock wave generated by the bolide should be optically thick once it has penetrated to an atmospheric density approximately 10(exp -6) gr/cm(exp 3), and we calculate the post-shock conditions assuming local thermodynamic equilibrium (LTE) for shock velocities v(sub sh) in the range 10 to 60 km/sec and preshock densities rho(sub a) = 10(exp -6) to 10(exp -2) gr/cm(exp 3). Our shock calculations include molecular hydrogen, atomic hydrogen, ionized hydrogen, neutral helium, and singly ionized helium. Even at the highest shock velocity, the gas is only partially ionized and the postshock temperature rises with preshock density in order to maintain the ionization. The value of the effective shock adiabatic index gamma(sub sh) varies from 1.17 (at low v(sub sh) and rho(sub a) to 1.40 (at high v(sub sh) and rho(sub a). The ablation rate is limited by the radiative flux that reaches the bolide surface. We argue that the ablated gas does not efficiently transfer its kinetic energy to the atmosphere, and it ultimately slows in a similar fashion to the comet material. As the bolide initially falls through the atmosphere, the character of the shock emission changes. At rho(sub a) approximately 10(exp -8) gr/cm (exp 3), the gas is optically thin and we expect line emission; in the optical spectrum, Balmer emission is expected from the shocked atmosphere and low-ionization metal lines from ablated cometary material. At rho(sub a) approximately 10(exp -6) gr/m(exp 3), the shocked gas is optically thick and the shock front near the bolide produces a blackbody spectrum. The temperature is favorable for ultraviolet (1000 to 3000 A) emission and the luminosity may be approximately 5 x 10(exp 23) ergs/sec for approximately 0.6 sec for a bolide 1 km in radius. At rho(sub a) approximately 10(exp -4) gr/cm(exp 3), the bolide has passed below the ultraviolet photosphere. The shock front emits considerable ionizing radiation, but it is absorbed in a narrow preshock region. The bolometric correction for the optical luminosity is large and we expect a 3000 to 8000 A luminosity of approximately 3 x 10(exp 23) ergs/sec for approximately 1 sec. The optical emission is strongly peaked in the vicinity of the bolide. The bolide does have a somewhat less luminous, optically thick trail extending greater than or equal to 10 km, but the radiation is characterized by a temperature of 4000 to 5000 K. From the fragmentation model of Chyba, Thomas, & Zahnle (1993), the bolide deposits most of its kinetic energy at rho(sub a) approximately 10(exp -3) gr/cm(exp 3) and this is the effective explosion site. The shock wave from such an explosion can move up about one density scale height. We examine the breakout of the shock front from the Jovian atmosphere and find that the shock acceleration in the decreasing density region is slow, so that the energy flux in the shock front is small. Higher velocities might be generated by shock acceleration along the channel left by the bolide if the shock motion can occur before the channel closes off as a result of radiative cooling. Hot gas created by the explosion ultimately rises due to buoyancy on a timescale of a minute. The luminosity is highest when the bubble first rises into the optically thin part of the atmosphere and may be approximately 1 x 10(exp 25) ergs/sec in the near-infrared. Roughly 1% of the initial bolide energy may be radiated in this way; the rest of the energy is lost to sound waves from the initial explosion and to work done by the bubble on the surrounding atmosphere.
Chevalier, Roger A.↗
Global oscillation amplitudes excited by the Jupiter-comet collision
The energy released during the collision of fragments of comet Shoemaker-Levy 9 with Jupiter in 1994 July may excite a spectrum of global oscillation modes. We estimate the maximum amplitudes to which the p-modes, discontinuity modes, inertial modes, and r-modes can be excited by assuming that the full kinetic energy of the fragment, which we take to be 10(exp 30) ergs, is converted into the energy of each individual mode. We have used two realistics Jovian models as the basis for our estimates: one with and one without the predicted 'plasma phase transition' (PPT) of hydrogen. A density discontinuity in the planet's hydrogen-helium envelope is associated with the PPT. We find that high-frequency p-modes, with periods approximately less than 15 minutes, may be excited to sufficiently large amplitudes to be observable as Doppler shifts (velocity amplitudes approximately greater than serveral m/s) or temperature variations (delta(T) approximately greater than 0.01 K) at the planetary surface. Inertial modes may also be observable. If the PPT exists in Jupiter, inertial modes with periods approximately 8 hr or approximately 2.2 days trapped in the surface region of the planet, above the PPT, may be detectable as temperature fluctuations of order delta(T) approximately 0.01 K. Inertial modes with periods of order 8-8.5 hr appear to be particularly strongly excited if the PPT exists. If the PPT does not exist in Jupiter, intertial modes with periods approximately 8-8.5 hr have much lower amplitudes. In this case, inertial modes with periods longer than approximately 18 hr may produce temperature fluctuations of order delta(T) approximately 0.01 K. Discontinuity modes associated with the PPT and r-modes unfortunately may not reach observable amplitudes.
Lee, U.↗
New jovian ring?
We follow the orbital evolution of small dust particles generated from the break up of comet Shoemaker-Levy 9 (SL9). In addition to the usual perturbations, we also consider electrostatic charging and the consequent magnetospheric effects. We show, that in about ten years following the break up, a small fraction of the dust will settle into orbits well inside the magnetosphere. The forming ring will be comprised of dust particles with radii in the range of 1.5 less than alpha less than 2.5 micrometers that follow retrograde orbits in the radial range of 4.5 less than r less than 6 R(sub J). We estimate the peak optical depth of this new ring in the range of 10(exp -8) less than tau(sub max) less than 2 x 10(exp -6).
Horanyi, Mihaly↗
Long-range consequences of interplanetary collisions
As Comet Shoemaker-Levy 9 races toward its mid-July collision with the planet Jupiter, considerable public attention is focused on catastrophic impacts with the Earth -- in the past and in the future. In recent years calls have been made to develop technologies that could deflect any asteroid or comet on a collision course. Careful consideration must be given to the nature and time scale of the risk and to the cost-effectiveness and possible problems in the suggested solutions. Risk assessment, threat removal, and resources misuse are examined. The greatest concern is to have a poorly informed public -- exerting pressure for means to mitigate even non-existent threats. The only foreseeable solution is a combination of accurate orbit estimation, realistic threat assessment, and effective public education.
Sagan, Carl↗
Impacts with the Earth and Jupiter
The Earth has been subject to impacts from comets and asteroids since its formation, and such impacts have played an important role in the evolution of life on our planet. We now recognize not only the historical role of impacts, but the contemporary hazard posed by such events. In the absence of a complete census of potentially threatening Earth-crossing asteroids or comets (called collectively Near Earth Objects, or NEOs), or even of a comprehensive current search program to identify NEOs, we can consider the hazard only from a probabilistic perspective. In general, the larger the object the greater the hazard, even when allowance is made for the infrequency of large impacts. Most of the danger to human life is associated with impacts by objects roughly 2 km or larger (energy greater than 1 million megatons), which can inject sufficient submicrometer dust into the atmosphere to produce a severe short-term global cooling with subsequent loss of crops, leading to starvation. Hazard estimates suggest that the chance of such an event occurring during a human lifetime is about 1:5000, and the global probability of death from such impacts is of the order of 1:20000, values that can be compared with risks associated with other natural hazards such as earthquakes, volcanic eruptions, and severe storms. The widely-observed impact of Comet Shoemaker-Levy 9 with Jupiter in July 1994 provides a graphic example of such an interplanetary collision and is stimulating worldwide interest in protecting our planet against cosmic impact catastrophes.
Morrison, David↗