****************************************************************************** * T h e M a r t i a n C h r o n i c l e * * October 1990 No. 5 * ****************************************************************************** The electronic newsletter by the International Mars Patrol (I.M.P.), an observing program of the Association of Lunar and Planetary Observers (A.L.P.O.) Edited by: J.D. Beish ------------------------------------------------------------------------------ ************************** MARS OBSERVER'S HANDBOOK ************************** * * * Now available from the Astronomical League is the Mars Observer's Handbook * * by Jeffrey D. Beish and Charles F. Capen at a new low price of $8.00. This * * very important and informative book is in second printing due to popular * * demand. Formerly published for The Planetary Society's Mars Watch '88, the * * book was sold out and has been out of print for the past two years. Send * * $8.00, check or money order to: Astronomical League Sales, Four Klopfer * * Street, Pittsburgh, PA 15209. * * * ****************************************************************************** Sand Ships of Mars Among one of the most exciting moments in a Mars observer's life is to catch a dust storm on Mars on the move. It is rare indeed when one can watch one of these great red clouds slowly move over the Martian landscape covering over features that were dark and well defined just hours before. While no two dust clouds are alike they nevertheless exhibit similar characteristics. Dust clouds are frequently confused with bright white areas, frosts, or localized fogs, and some dense white clouds. In addition, after identification is made, it becomes difficult to distinguish active dust clouds from fresh surface dust deposits. Such misinterpretation can make time studies difficult. A careful diagnosis of observational records of Mars from 1877 through the seventeen perihelic apparitions since 1907 show evidence that Martian dust storms have evolved in preferred southern locations near the latitude of maximum insolation. Maximum insolation occurs during Martian southern summer which corresponds to the terrestrial months of August, September, and October of perihelic apparitions (Capen and Martin, 1972). Recent studies of Martian dust storms reveal three periods in the Martian year when dust clouds and/or storms are most likely to occur. These periods correspond to 105 dg Ls* (northern summer), 255 dg Ls (southern spring), and 315 dg Ls (southern summer). [Beish and Parker, 1990]. * NOTE: Ls is the Planetocentric Longitude of the Sun. Since 1971, the year of the "Great Dust Storm of Mars," the ALPO Mars Recorders have suspected that these disturbances come in pairs. We have seen that in 1971 a major dust storm occurred on 213 dg Ls, followed by a "planet encircling" dust storm on 260 dg Ls. Again, in 1973 a major storm began on 244 dg Ls and was followed by a "planet encircling" storm on 300 dg Ls. The Viking Lander recorded two "planet encircling" storms on 204 and 268 dg Ls. Although the two dust storms of 1988 did not reach the "planet encircling" stage, similar patterns emerged; during 206 dg Ls a major storm occurred, followed by another major storm on 313 dg Ls. Perhaps the statistical significance of the three periods above appear to mislead us when attempting to predict when these disturbances should occur. However, one should be especially alert when observing Mars during these times -- even though we have passed through the first sensitive period, be watchful in the next few weeks, alas, a major dust storm may be lurking just around the corner! REPORTING MARTIAN DUST CLOUDS AND STORMS In analyzing the IMP data, the ALPO Mars Recorders have had to exercise considerable caution in defining dust clouds. They have applied the following criteria: 1. The sine qua non of Martian dust clouds is movement with obscura- tion of previously well-defined albedo features. Absence of this criterion in the present study disqualified a candidate from inclusion under dust clouds [Beish, et al, 1990]. 2. They are bright in red light. Repeat -- bright in red light! 3. Often, when these clouds reach heights of several kilometers, they may cast shadows -- that are observable from Earth. There are numerous reports of anomalous transient dark surface markings appearing near dust clouds, espe- cially when the solar phase angle was reasonably large [Slipher, 1962]. A DUST CLOUD IN OCTOBER 1990 During the first week of October 1990 the phone at ALPO's International Mars Patrol headquarters began to ring. News of bright spots on Mars, "maybe a dust cloud or something," scoffed the cautious observers. Their words were restrained and with good reason -- past experience has taught them not to jump to conclusions, especially about this Martian dust storm business. After all, these storms are very rare and often mislead the most experienced Martian dust storm watchers! The genesis of the latest disturbance began on September 25, 1990. Re- porting from Paragould, Arkansas, Kermit Rhea noted that Chryse appeared brighter than usual from the 25th. of September through October 2nd. His observations indicate unusual activity in the regions of Chryse and Xanthe. Don Parker, fearful of awaking my family, avoided calling me while he observed Mars at 0400 UT on October 4th (310 dg Ls), suspected that the bright streak bordering northern Aromatum Promontorium in the south of Chryse might be the beginning of a dust storm. The following night (310.5 dg Ls) this Mars Recorder watched with delight as the dust cloud, correctly identi- fied by Parker the night before, had moved southwest onto Eos, partially obscuring Aurorae Sinus with what appeared as a bright oval spot followed by a long streak. The morning side of Mars had lost its usual effect of limb darkening and was replaced by a bright haze extending 10 degrees into its morning. Subsequent visual reports and photographs show that a dust cloud extended from eastern Margaritifer Sinus (30W, 0N) to just south of Aurorae Sinus. October 6th. (311 dg Ls) brought more meteorological delights, white clouds now laced much of the morning limb and portions of Chryse, even a bright white cloud was seen on the limb just to the north of Sabaeus Sinus. Morning hazes were even brighter, extending 15 to 20 degrees away from the limb. The dust cloud of October 5th. had moved 575 miles further southwest, now obscuring the southern half of Aurorae Sinus and completely covered Eos (40W, 12S). A dull streak or "dusty trail" was observed to extend from the southeast of Aurorae Sinus over into Ophir -- one of the brightest areas on the planet Mars. Observers on October 7th. (311.8 dg Ls) reported an increase in meteorol- ogy on Mars. Clouds had formed over Deucalionis Regio, Aram, and in the crea- tor Eros. Several discrete clouds in Chryse mixing with white morning limb clouds and hazes. The main dust cloud had moved west-southwest anther 475 miles to 50W, 20S). A peculiar Y-shaped dust cloud hung over Aurorae Sinus extending into Ophir as if transferring dust particles in that region from the main disturbance. One asks what would have crossed Ray Bradbury's mind while viewing such splendor -- might he think it was Martians on the run in their sand ships? At last, the next day the small Martian dust storm appeared to be over. With perfect on October 8th. (312 dg Ls), this Mars observer saw a familiar Martian landscape, with only a few alterations to the usually dark and well defined Aurorae Sinus. Eos appeared to have grown a little. As expected, a dull dusty haze covered the south polar region and the morning limb was bright with blue and reddish hazes [Beish et al, 1984]. Oh yes, all was quite again on Barzoom, lest we not forget Edgar Rice Burroughs. CONCLUSION Although the October 4th. - 7th. dust disturbance is not considered a major storm it was a significant meteorological activity. Moving over 1,000 miles of the Martian landscape it did alter small portions of previously dark and well defined features. A secondary dust cloud appeared in Ophir, an area over 650 miles west of the main dust cloud, on October 7th. We can theorize that dust clouds on Mars may erupt in more than one place if the conditions are right. Past observations of Martian dust storms indicate that the Red Planet was very near its peak dust storm period at 315 dg Ls. [Beish et al, 1990]. Remember, 315 dg Ls will fall on October 18, 1990! REFERENCES Beish, J.D., and D.C. Parker, "Meteorological Survey of Mars, 1968-1985," Journal of Geophysical Research, Vol. 95, B9, August 20, 1990. Beish, J.D., Parker, D.C., and Capen, C.F., "A Major Martian Dust Storm in 1984", J.A.L.P.O., Vol. 30, Nos. 9-10, August 1984. Capen, C.F., and L.J. Martin,"Survey of Martian Yellow Storms." Bull. Amer. Astron. Soc. 4, 374, 1972. Capen, C.F., "A Martian Yellow Cloud - July 1971." Icarus, 22, 345-362, 1974. Slipher, E.C., "Mars, The Photographic Study. Northland Press, Flagstaff, AZ, 108-109, 1962. ******** Introduction to Observing and Photographing the Solar System ******** * * * Picked as one of the top twelve non-technical astronomy books of 1989 by * * the ASP, Introduction to Observing and Photographing the Solar System, * * by T.A. Dobbins, D.C. Parker, and C.F. Capen contains both theoretical and * * observational information on Solar System objects. Very detailed chapters * * on Mars, astrophotography, micrometry, etc. Forward by A.L.P.O. founder * * Walter H. Haas. Hardcover, $19.95 from Willmann-Bell, Inc., P.O. Box 35025 * * Richmond, VA 23235, (804) 320-7016. * * * ******************************************************************************