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