Explosion of comet Shoemaker-Levy 9 on entry into the Jovian atmosphere

We use the astrophysical hydrocode ZEUS to compute high-resolution models of the disruption and deceleration of cometary fragments striking Jupiter. We find that simple analytic and semianalytic models work well for kilometer-size impactors. We show that previous numerical models that placed the explosion much deeper in the atmosphere failed to fully resolve important gasdynamical instabilities. These instabilities tear the comet apart, greatly increase its effective cross section, and bring it to an abrupt halt. A 1 km diameter fragment loses over 90% of its kinetic energy within a single scale height at an atmospheric pressure of order 10 bars. For all practical purposes, it explodes.     

On penetration depth of the Shoemaker-Levy 9 fragments into the Jovian atmosphere

The actual penetration depth of the Shoemaker-Levy 9 fragments into the Jovian atmosphere is still an open question. From fundamental equations of meteoric physics with variable cross-section, a new analytic model of energy release of the fragments is presented. In use of reasonable parameters, a series of results are calculated for different initial mass of the fragments. The results show that the largest fragment explodes above pressure levels of 3 bars and does not penetrate into the H₂O cloud layer of the Jovian atmosphere, and that airburst of smaller fragments occur even above the upper cloud layer.     

Positional and photometric CCD observations of the comet Shoemaker-Levy 9

Positional and photometric CCD observations of the comet Shoemaker-Levy 9 fragments were carried out at the Abastumani Astrophysical Observatory. Up to 15 named fragments were detected and their equatorial coordinates and magnitudes are reported. CCD frames were processed using DAOPHOT II. The internal precision of reference star positions down to 18^m is 0.″7 and the mean error of photometry does not exceed ±0.3 mag.     

Sodium emission from Comet Shoemaker-Levy 9 in the magnetosphere of Jupiter

On July 20, 1994, before the Q fragments of Comet Shoemaker-Levy 9 fell to Jupiter, more than 200 spectra of the Jovian features were obtained at the Crimean Astrophysical Observatory in the wavelength range 5700–7600 Å with a 26 s exposure time and a spectral resolution of 20 Å. We found a time-varying Na D line emission in the form of two components with Doppler shifts of about 30 Å. The brightest and most frequent sodium flares were detected when the Q fragments passed through the Jovian inner magnetosphere at a distance of about three the Jovian radii (3R_J) from its center, where they crossed the Io-Jupiter current tube. A frequency analysis of our data revealed a flare recurrence time scale of 1 min. We conclude that sodium was released from the cometary dust and from the surfaces of numerous cometary debris and that its amount was enough to produce the observed emission. The observed high-speed clouds of sodium atoms are assumed to have been formed through ionization, ion acceleration by the bidirectional electric fields of Alfvén waves in the Io-Jupiter current tube, and their neutralization.     

Peculiar oscillations in the microwave emission of Jupiter during the impact of K fragment of comet Shoemaker-Levy 9

In this article we report the peculiar oscillations in the intensity of microwave (4.15 GHz) emission seen during the impact of K fragment of comet Shoemaker-Levy 9 on July 19, 1994. The oscillations begin at 10h 13m 25s UT suddenly with a frequency of ~0.3 Hz and gradually the frequency of these oscillations increases to ~ 1 Hz. The oscillations are not due to local atmosphere or the radio interference from signals of geostationary satellite. They are intrinsic to the microwave emission from Jupiter during the impact of K fragment. Peak-to-peak amplitude of the oscillations is about 34% of the total microwave emission from Jupiter. If we assume that only 50% of the microwave emission is non-thermal and only the non-thermal emission suffered oscillations, then the oscillations are about 68% of the non-thermal emission from Jupiter. The observations also indicate that there are three continuum enhancements during this event and periodic oscillations almost all through. The third enhancement was the largest and during this enhancement there were some additional aperiodic variations. The aperiodic variations were of the order of few minutes and were possibly generated by the gravity waves. The periodic oscillations could be synchrotron emission modulated by the plasma oscillation in the outer magnetosphere. kg]Key words     

X-ray observation of the Jovian impacts of comet Shoemaker - Levy 9

An ASCA observation of the Jovian impact of the comet Shoemaker-Levy 9 is reported. Four impacts of H, L, Q1 and R were observed and four impacts of B, C, G, and Q2 were observed within 60 minutes after their impacts. No significant flaring of X-ray emission was observed. Upper limit X-ray fluxes of 90 % confidence level, averaged 5 minutes just after the impacts, were 2.4 × 10^–13 erg sec^–1 cm^–2, 3.5 × 10^–13 erg sec^–1 cm^–2, 1.6 × 10^–13 erg sec^–1 cm^–2 and 2.9 × 10^–13 erg sec^–1 cm^–2 for the impacts of H, L, Q1 and R, respectively, in the 0.5(0.7 for H and Q1)–10 keV energy range. However, a hint of X-ray enhancement around Jupiter from July 17 to July 19 was detected with about 2 6 × 10^–14 erg sec^–1 cm^–2 in the 0.5–10 keV energy range.     

Electromagnetic radiation outbursts from the collision of P/Shoemaker-Levy 9 comet with Jupiter

The forthcoming collision by debris of P/Shoemaker-Levy 9 comet with Jupiter during the week of July 18, 1994 has generated considerable scientific and public interest. This collision may release an amount of energy ranging from 10²⁵-10³¹ ergs in the Jovian atmosphere. Two possible phenomena associated with this event are described in this Letter to the Editor. The first one is the likely display of deformed Jovian magnetic field lines as the comet interacts with the Jovian magnetosphere. The second one is electromagnetic radiation outbursts during comet explosions over a wide frequency range from radio up to gamma ray emissions. If relativistic electrons with energies up to ~ 1000 MeV could be produced during comet explosions, then synchrotron radiations with frequencies from radio up to infrared range could be detectable. Hard X-rays and gamma rays could be produced by bremsstrahlung and inverse Compton processes. Since one cannot exclude the possible transient presence of relativistic electrons with Lorentz factor 2 × 10⁶, synchrotron radiation component might even be extended into gamma ray frequency range during intermittent short time intervals.     

Jovian emission at 18 cm during the comet S-L 9 impacts observed with RATAN-600 radio telescope

The monitoring of Jupiter synchrotron emission at 18 cm from July 15 till July 31 has shown a large flux density increase up to 29 per cents near July 22 and less but obvious disturbance in the next week.     

Effects of shape and spin on the tidal disruption of P/Shoemaker-Levy 9

I derive an approximate criterion for the tidal disruption of a rubble pile body as it passes close to a planet (or the sun): % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqyWdi3aaS% baaSqaaiaacogaaeqaaOGaeyisIS7aamWaaeaacaaIYaGaeqyWdihd% caWGWbGccaGGDbWaaeWaaeaadaWcaaqaaiaadkfamiaadchaaOqaai% aadkhaaaaacaGLOaGaayzkaaWaaWbaaSqabeaacaaIZaaaaOGaey4k% aSYaaeWaaeaadaWcaaqaaiabeM8a3bqaaiabeM8a3XGaaGimaaaaaO% GaayjkaiaawMcaamaaCaaaleqabaGaaGOmaaaaaOGaay5waiaaw2fa% amaabmaabaWaaSaaaeaacaWGHbaabaGaamOyaaaaaiaawIcacaGLPa% aacaGGSaaaaa!5229!\[\rho _c \approx \left[ {2\rho p]\left( {\frac{{Rp}}{r}} \right)^3 + \left( {\frac{\omega }{{\omega 0}}} \right)^2 } \right]\left( {\frac{a}{b}} \right),\] where _c is the critical density below which the body will be disrupted, _p is the density of the planet (or sun), R _p is the radius of the planet, r is the periapse distance, is the rotation frequency of the body, ₀ is the surface orbit frequency about a body of unit density, and a/b is the axis ratio of the body, considered as a prolate ellipsoid. For P/Shoemaker Levy 9, in its passage close to Jupiter in 1992, this expression suggests that the critical density is ~1.2 for a spherical, non-spinning nucleus, but could be >2.5 for a 2:1 elongate body with a typical rotation period of ~10 hours.     

Effects of shape and spin on the tidal disruption of P/Shoemaker-Levy 9

I derive an approximate criterion for the tidal disruption of a “rubble pile” body as it passes close to a planet (or the sun): % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqyWdi3aaS% baaSqaaiaacogaaeqaaOGaeyisIS7aamWaaeaacaaIYaGaeqyWdihd% caWGWbGccaGGDbWaaeWaaeaadaWcaaqaaiaadkfamiaadchaaOqaai% aadkhaaaaacaGLOaGaayzkaaWaaWbaaSqabeaacaaIZaaaaOGaey4k% aSYaaeWaaeaadaWcaaqaaiabeM8a3bqaaiabeM8a3XGaaGimaaaaaO% GaayjkaiaawMcaamaaCaaaleqabaGaaGOmaaaaaOGaay5waiaaw2fa% amaabmaabaWaaSaaaeaacaWGHbaabaGaamOyaaaaaiaawIcacaGLPa% aacaGGSaaaaa!5229!\[\rho _c \approx \left[ {2\rho p]\left( {\frac{{Rp}}{r}} \right)^3 + \left( {\frac{\omega }{{\omega 0}}} \right)^2 } \right]\left( {\frac{a}{b}} \right),\] where ? _c is the critical density below which the body will be disrupted, ? _p is the density of the planet (or sun), R _p is the radius of the planet, r is the periapse distance, Ω is the rotation frequency of the body, Ω₀ is the surface orbit frequency about a body of unit density, and a/b is the axis ratio of the body, considered as a prolate ellipsoid. For P/Shoemaker Levy 9, in its passage close to Jupiter in 1992, this expression suggests that the critical density is ~1.2 for a spherical, non-spinning nucleus, but could be >2.5 for a 2:1 elongate body with a typical rotation period of ~10 hours.     

Observation of collision of comet Shoemaker-Levy 9 with Jupiter at the Astronomical and Geophysical Observatory in Modra

A report about observations of collision of the comet Shoemaker-Levy 9 with Jupiter is presented. The observations were made both in optical and radio wavelengths. Some consequences of impacts of individual fragments of the comet were detected visually in the 20-cm refractor. 21 days prolonged series of records on a video tape was taken in the focus of the 60-cm reflector, too. 13 serious events from July 16, 1994 to July 23, 1994 on 42.7 MHz radio wavelengths were registered. Its coherence with the pair Shoemaker-Levy 9 and Jupiter in the interaction is the subject of further investigation. More comprehensive results will be published after collecting information about similar observations on radio waves all over the world.     

Submicron dust and the collision of comet SL-9 with Jupiter

Sub-micron sized dust grains released from the several fragments of the comet Shoemaker-Levy 9 could produce significant observable effects on the colour of the Jovian surface. Analysis of photometric data could lead to important insights into the nature and quantity of the dust, as well as the release mechanisms involved.     

The composition of very fine dust in the dust shell of comet halley

An analysis of the spectra from the PUMA dust-impact mass spectrometers onboard the Vega-1 and Vega-2 spacecraft shows that a large number of the observed, unidentified small-amplitude peaks are produced by impacts of very-low-mass (from 10^?17 to 10^?20 g) particles. The mass flux of very fine particles accounts for a few percent of the total dust mass flux from comet Halley. The elemental composition of the finest cometary particles is identical to the composition of large particles (10^?12–10^?16 g), in agreement with present views about the nucleus of comet Halley as an aggregate of interstellar dust.     

Jovian decametric events during the period of the impacts of SL-9

Strong decametric narrow-band radio bursts, produced by impacts of fragments D, E, G, K, N, S and W of Comet Shoemaker-Levy 1993e (SL-9) on the Jupiter, have been detected during our observations from July 17 to 22, 1994 at the Xin-Xiang temporary Jovian Decametric Station of Beijing Astronomical Observatory. Plots of relative signal intensity of these bursts at 10 frequencies between 24.0 and 28.5MHz are presented. The major features of events are sumarized and discussed.The project is supported by the National Natural Science Foundation of China.Correspondent of this paper. Dr. Han is leaving from Beijing for the Astronomical Center of Zielona Gora, Pedagogical University, ul. Lubuska 2, 65 265 Zielona Gora, Poland to be a post-doctor. Contact with him by email HJL@bao01.bao.ac.cn or by airmail to Poland.     

The charged particle in the magnetosphere of a rotating neutron star

The motion of charged particles in a pulsar magnetosphere is examined in the present paper. Using the non-relativistic approximation, the trajectories of the charged particles are investigated qualitativley both in the case of axial and in the case of incline rotator. The obtained results can be used for the construction of the pulsar magnetosphere.     

彗木相撞中的波动

1994年7月18日至24日期间，彗星苏梅克-列维9(SL-9)的超过20块碎片与木星发生了相撞．哈勃空间望远镜(HST)拍摄到的图像揭示了木星大气对撞击的动力学响应．具有重要意义的是观测到5个撞击点周围的圆环，它们以450米／秒的常速度向外运动．环的圆形性表明它们是波．因为对于不同大小的撞击，波速是常量，可以推断出传播速度与爆炸能量无关．这意味着这些波动是线性波．评述现行理论所使用的3类候选波，亦即惯性引力波、声波和地震波，介绍的重点是前面两种．     

彗木相撞中的惯性引力波

苏梅克-列维9号彗星(SL9)与木星相撞后，在木星上观测到的以常速度(～450m／s)向外扩展的圆环意味着这是碰撞在木星大气中引起的线性波动．我们选取：非旋转、无粘性、密度分层、不可压缩的木星大气模型，而且木星大气以水平速度U=b az运动；给出初始扰动压力P(r；0)作为碰撞的初始条件，用流体力学方程组求解了彗木相撞中的惯性引力波．结果表明：当木星大气以速度U=U0(～170m／s)运动时，彗星碎片的大部分能量都用来产生内波，同时还得到彗星碎片的撞击深度H与水平相速Vp的关系式．当木星大气以速度为U=b az运动时，木星大气的扰动能量不再是在动能和势能间均分。