From PWC@GRAVI.JPL.NASA.GOV Tue Jul 5 23:04:44 1994 From PWC@GRAVI.JPL.NASA.GOV Tue Jul 5 23:04:44 1994 Below is the July 5 edition of our Predicted Impact Parameters table. This set of predictions is particularly important because the Galileo observation sequences will be keyed to the these impact times. The orbit solutions for these predictions were based on very recent astrometric positions, some of them obtained as late as yesterday, July 4! Helping matters further, some of the new measurements were reduced using the pre- release Hipparcos star catalog, making them highly accurate. We thank the many observers and measurers who worked long hours over the weekend to provide us with the very latest data. The predicted impact times are generally about 5 to 10 minutes earlier than those in our table of June 24, at least for the major fragments. The times for fragments A and D made the largest jumps (24 and 29 minutes later), and the time for W jumped 19 minutes earlier. Jumps like these are generally due to small measurement errors in the latest data used in the solution. Because of the new data, the impact time uncertainties have dropped substantially, down into the 6-8 minute range for many of the fragments. We expect future jumps in predicted impact times to be correspondingly smaller. Starting with this version of the table, we provide impact times to the nearest second, even though that is well below our current level of accuracy, and we provide impact time uncertainties to the nearest tenth of a minute. Paul Chodas 1994 July 5 ============================================================================== Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9 --------------------------------------------------------------- P.W. Chodas, D.K. Yeomans and Z. Sekanina (JPL/Caltech) P.D. Nicholson (Cornell) Predictions as of 1994 July 5 Date of last astrometric data in these solutions: 1994 July 4 The predictions for all fragments except Q2 are based on independent orbit solutions; our orbit reference identifier is given. The orbit solution for fragment Q2 was obtained by applying a disruption model to the orbit for Q1, and using astrometric measurements of Q2 relative to Q1. Except for fragment Q2, uncertainties in the impact parameters are given immediately below the predicted values. These uncertainties are 1-sigma values obtained from Monte Carlo analyses; we have made an effort to make them realistic: they are not formal uncertainty values. NOTE: To obtain a 95% confidence level, one should use a +/- 2 sigma window around the predicted values. The uncertainties for Q2 have not been quantified, but are probably comparable to those for fragment T. The dynamical model used for these predictions includes perturbations due to the Sun, planets, Galilean satellites and the oblateness of Jupiter. The planetary ephemeris used was DE245. ------------------------------------------------------------------------------- Frag- Impact Jovicentric Merid. Angle Satellite Longitudes ment Date/Time Lat. Long. Angle E-J-F Orbit at Impact (deg) July (UTC) (deg) (deg) (deg) (deg) Ref. Amal Io Eur Gany ------------h--m--s------------------------------------------------------------ A = 21 16 19:53:40 -43.08 175 64.05 99.04 A18 203t 344 106+ 76+ 8.4 .19 5 .77 .57 4 1 1 0 B = 20 17 02:49:03 -43.04 67 63.54 99.40 B17 52+ 42+ 136+ 91+ 8.3 .20 5 .75 .56 4 1 1 0 C = 19 17 06:55:36 -43.22 215 64.85 98.42 C14 175t 77+ 153+ 99+ 8.4 .17 5 .74 .55 4 1 1 0 D = 18 17 11:41:50 -43.45 27 65.27 98.08 D16 319 117+ 173 109+ 8.7 .18 5 .77 .57 4 1 1 0 E = 17 17 15:03:51 -43.42 149 65.78 97.72 E31 61+ 146+ 187 117+ 8.0 .08 5 .48 .34 4 1 1 0 F = 16 18 00:28:15 -43.52 131 64.49 98.61 F22 344o 226 226 136+ 6.8 .12 4 .57 .41 3 1 0 0 G = 15 18 07:28:00 -43.58 23 66.60 97.09 G30 194t 286 255 151+ 5.7 .07 3 .38 .27 3 1 0 0 H = 14 18 19:25:48 -43.70 96 66.87 96.86 H29 194t 27+ 305 176 5.6 .07 3 .38 .27 3 1 0 0 K = 12 19 10:17:58 -43.77 275 67.76 96.21 K30 282 152+ 8+e 207 6.5 .07 4 .40 .28 3 1 0 0 L = 11 19 22:06:58 -43.88 343 68.11 95.93 L31 278 253 59+ 232 6.1 .07 4 .39 .28 3 1 0 0 N = 9 20 10:18:37 -44.19 65 67.80 96.09 N19 285 356 o 111+ 257 8.6 .12 5 .68 .48 4 1 1 0 P2= 8b 20 15:05:10 -44.53 240 66.40 97.01 P17 69+ 37+ 132+ 267 7.4 .09 4 .59 .41 4 1 1 0 Q2= 7b 20 19:31:36 -44.31 39 68.86 95.32 202t 74+ 150+ 277 Q1= 7a 20 19:59:04 -44.02 55 69.28 95.07 Q34 216 78+ 152+ 278 7.3 .07 4 .41 .29 4 1 1 0 R = 6 21 05:22:04 -44.05 35 69.28 95.06 R28 138 157 191 297 7.2 .08 4 .47 .33 4 1 1 0 S = 5 21 15:07:13 -44.13 28 69.72 94.73 S38 72+ 240 232 318 6.9 .08 4 .42 .29 3 1 0 0 T = 4 21 18:04:14 -44.99 138 67.37 96.23 T12 161t 266 244 324 15.2 .16 9 1.00 .70 8 2 1 1 U = 3 21 21:47:00 -44.47 271 68.68 95.41 U13 273 297 259 332 16.1 .19 10 1.13 .79 8 2 1 1 V = 2 22 03:57:25 -44.31 135 68.43 95.60 V13 99+ 349 285 345 12.4 .17 7 1.00 .71 6 2 1 0 W = 1 22 07:53:17 -44.17 276 70.23 94.36 W30 217 23+ 302 353 9.1 .10 6 .53 .37 5 1 1 0 Satellite Codes: + impact is visible from satellite o satellite is occulted by Jupiter at impact e satellite is eclipsed but not occulted at impact t satellite is in transit across Jupiter ------------------------------------------------------------------------------- Notes: 1. Fragments J=13, M=10, and P1=8a are omitted because they have faded from view. The March'94 HST images show that P2=8b and G=15 have split; we do not have sufficient data to obtain independent predictions for the sub-components. 2. The impact date/time is the time the impact would be seen at the Earth (if the limb of Jupiter were not in the way); the date is the day in July 1994; the time is given as hours and minutes of Universal Time. The impact time uncertainty is a 1-sigma value in minutes. 3. The impact latitude is Jovicentric (latitude measured at the center of Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative. 4. The impact longitude is System III, measured westwards on the planet. The large uncertainty in impact longitudes is due to Jupiter's fast rotation. 5. The meridian angle is the Jovicentric longitude of impact measured from the midnight meridian towards the morning terminator. This relative longitude is known much more accurately than the absolute longitude. At the latitude of the impacts, the Earth limb is at meridian angle 76 deg and the terminator is at meridian angle 87 deg. 6. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater than 90 deg indicate a farside impact. All impacts will be just on the farside as viewed from Earth; later impacts will be closer to the limb. 7. Satellite longitudes are given for Amalthea, Io, Europa, and Ganymede. The longitudes are measured east from superior conjunction (the anti-Earth direction). Longitude uncertainties listed as "0" are simply < 0.5 deg. 8. According to these predictions, the only impact certain to occur during a satellite eclipse is K=12 with Europa eclipsed. --------------------------------------------------------------------------- NATURE ARTICLE ON THE COMET CRASH BY PAUL WEISSMAN