................................................................. . = T H E M A R T I A N C H R O N I C L E = . . . . The electronic newsletter by the International Mars Patrol, . . an observing program of the . . Association of Lunar and Planetary Observers . . Edited by: J.D. Beish . . June 1991 No. 6 . ................................................................. 1990-1991 OBSERVATIONAL SUMMARY Although participation fell short of the 7,063 observations turned in during 1988, the Association of Lunar and Planetary Observer's International Mars Patrol program successfully con- vinced seventy-five Mars observers to watch the Red Planet in 1990 and 1991. Using 95 telescopes, these dedicates astronomers contributed 1,669 visual, multi-colored photographic observations of Mars, polar cap measurements, and 44 video tapes of CCD images during the 1990-91 apparition of Mars. During this period, the planet's south pole was tilted toward Earth, allowing detailed observations of the highly cratered and topographically interesting southern hemisphere of the Red Planet Mars. A Mars apparition is a period that useful observations the Red Planet can be obtained and usually covers one or more Earth years. Mars has an average 15.8-year seasonal opposition cycle, which consists of three or four aphelic oppositions and three consecutive perihelic oppositions. The 1990-91 apparition was considered transitional because opposition occurred almost exact- ly 90 degrees of perihelion. Mars reached opposition on November 27, 1990 and was closest to Earth on November 20, 1990 with a distance of 48,050,617 miles (77,330,127 km) and an apparent disk diameter of 18.10 arcsecs. Gerard Teichert of Hattstatt, France was the first and last to send observations of Mars during the last apparition. Apparition observational coverage was adequate, with 54% of the Martian year being observed. The study of dust storms has been one of the priorities of the IMP. The dust program has two goals: 1) to alert professional astronomers as soon as dust clouds are detected, and 2) to moni- tor the progression and boundaries of the dust clouds. The system worked well for the two dust storms of 1988, but it was the 1990 apparition that provided the opportunity to demonstrate the true international character of the IMP. MARTIAN DUST STORMS OF 1990 One of the most exciting events for the Mars observer is to catch a dust storm on the move. It is rare indeed when one is abler to watch great dust clouds slowly move over the Martian landscape, covering features previously were dark and well defined, just hours before. While no two dust clouds appear the same 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. TRANSIENT DUST CLOUDS OF OCTOBER During the first week of October 1990 the phone at ALPO's International Mars Patrol (IMP) 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 led them to a more con- servative approach and 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 these dust disturbances may be a sudden increase in meteorology in one of the dust sensitive areas on Mars. Reporting from Paragould, Arkansas, Kermit Rhea noted, on September 25, 1990, that Chyrse (where Viking 1 Lander sits) appeared brighter than usual over an extended period of time. His observations indicated unusual meteorological activity in several regiopns on Mars. On 03 October, Dan Troiani observed Chryse as very bright in red light, indicating possible dust activity. The next day, 04 October, calling from New York, Frank Melillo reported to the ALPO Mars Recorders a dust cloud in Chryse. On October 4th, the Recorders observed a bright streak bordering northern Aromatum Promontorium, in the south of Chryse, and suspected it might be the beginning of a dust storm. The following night the we watched with delight as the dust cloud had moved southwest of Chryse. The morning side of Mars had lost its usual effect of limb darkening and was replaced by a bright pole to pole haze. Subsequent visual reports and photographs show that a dust cloud extended 575 miles further southwest. The next day, 07 October, the main dust cloud had moved west southwest another 475 miles to a longitude of 50W and latitude of 20S. A peculiar Y-shaped dust cloud hung over Aurorae Sinus that extended into Ophir, (regions near the great canyon Vallws Mari- neris). At last, the next day the small Martian dust storm appeared to be over. With perfect "seeing" on October 8th the Mars Recorders saw a familiar Martian landscape. Only a few alterations to the usually dark and well defined "maria" were obvious. The morning limb was bright with blue and reddish hazes. TRANSIENT DUST CLOUDS OF NOVEMBER Observational reports of unusual atmospheric activity in Chryse on 31 October. CCD images by T. Platt of England reveals what must be a dust cloud over Chryse-Candor. Dust clouds were definitely identified on 04 November by ALPO's Frank Melillo. Don Parker's photographs from 04 through 09 November show several small bright and well defined dust clouds crossing from Chryse over Aurorae Sinus onto Solis Lacus (The Eye of Mars!) By 04 November 1990 observers reports agreed remarka- bly as to the size and distribution of three dust clouds located over the Solis Lacus region. Analyzing the IMP drawings and photographs from 5 and 6 Novem ber suggested that there was more than one dust storm occurring- on Mars. The multiple character of the storm was verified by a CCD photo taken at the Pic-du-Midi Observatory on 5 November (see top right photo on cover of S&T, June 1991). With the Martian central meridian at approximately 30 dg, this image shows numer- ous foci of dust obscuring: 1) western Nilokeras and Lunae L., 2) Agathadaemon, Melas L., and southern Aurorae S., 3) the north eastern border of Solis L., and 4) southeastern Thaumasia Foelix, approximately 80W, 40S. In addition, Chryse and Xanthe were much lighter than normal, suggesting diffuse dust in these regions. By 6 November the character of the dust storm complex began to repidly change. Detailed drawings by Rogers, Jacobson, and Boyar and high resolution photographs by Parker and Beish, who was employing the University of Hawaii's 24-inch Cassegrain on Mauna Kea, showed three brilliant spots in the vicinity of Solis Lacus. All were very bright in red light. The first lay over northwest Solis Lacus, at 90W, 22S, obscuring approximately 30% of this feature. European observations of regions to the east of Solis Lacus revealed a return of visibility of Aurorae Sinus and Ganges, although some dust remained in Eos, with bright fingers of cloud extending northeastward into Chryse. Some dust was also reported crossing Bosporus into Argyre I. Nearly all observers commented on the dullness and irregular shape of the North Polar Hood (NPH). By 11 November members of the OAA had taken up the study of this southern dust cloud. It appeared as a whitish mist across Bosporos. Superb drawings and photographs by Minami and Miyazaki place its western boundary near 120W on 11 November. By 13 Novem- ber this boundary was still 115 dg., but the cloud had thinned considerably. Bosporos became faintly visible on 14 November, and the western boundary of the Thaumasia Foelix dust cloud was estimated at 65-70 dg.W. By 15 November Bosporus was again well defined, and Mars appeared free of obscurations. Both U.S. and Japanese observers failed to find evidence of residual dust. The Martian atmosphere had cleared very rapidly indeed. POLAR REGIONS During both the October and the November storms, most observ ers reported that the North Polar Hood (NPH) underwent signifi- cant changes, becoming dull and broken. Photographs and drawings from both periods show albedo features visible beneath the hood, suggesting a thinning of the canopy at those times. The NPH appeared to diminish in size and intensity between 5 and 7 Octo- ber. On 8 October the Martian north polar region was again bril liant, but in reviewing the observations, there is some question about whether it was the hood that was seen or perhaps the North Polar Cap shining through a thinned hood. Unfortunately not enough color filter work was done on the polar regions to answer this question. The behavior of the NPH followed much the same pattern during the November dust outbreaks. It became dull on 5 November and by 7 November albedo features in Mare Boreum could be seen through it, giving the hood a broken appearance. By 9 November the hood appeared somewhat brighter in red and integrated light than in violet, suggesting the appearance of the cap. Over the next several days this condition persisted, but by 18 November the North Polar Hood had returned to normal. The South Polar Cap (SPC) was visible throughout both the October and November dust storms. Although antarctic hazes were frequently sighted during these periods, observers employing large apertures and color filters were able to see the SPC through early December. THE 1990 - 1991 METEOROLOGY OF MARS Classified by the color, bright Martian atmospheric clouds and hazes are best observed using a blue or violet filter and fre- quently cross-checked with those made in red light for atmospher- ic penetration. Without the aid of color filters, condensates in the atmosphere of Mars is difficult, if not impossible, to de- tect. Clouds and hazes were rare during the first ten months of the apparition. It is not unusual for Mars' atmosphere to be clear during its southern spring and summer. Cloud activity increases during Martian southern autumn. (NOTE: Mars has four seasons similar to Earth, we see both hemispheres and becomes confusing if the hemisphere is not labeled). The atmosphere of Mars became dusty after two transient dust storms appeared during October and November 1990 (discussed above). As result, an in- crease in meteorology became apparent from late November onward. Martian meteorological activity remained minimal until September 1990. Observers employing blue and violet filters were able to detect a few interesting clouds and hazes in Chryse, Candor, and Tharsis. Intermittent morning limb hazes recorded by IMP observers during April, May, and June 1990. By the end of July morning limb hazes began to be reported with increasing frequency. Photo- graphs by Isao Miyazaki, Parker, and others, and visual reports during August and September show morning limb hazes had developed from the south polar region to the north polar region. Morning limb hazes fell off during late Martian southern summer. As a result of the dust storm in October, morning limb haze increased in extent and brightness beginning on 05 October. Again, the morning limb haze became bright and prominent on 04 November. Evening limb haze only reported only a few times during mid-November 1990. By late summer and early spring, evening limb became increasing hazy. Martian clouds were also reported after the November dust storm. Recurrent topographic clouds are dense whitish clouds of limited extent. They occur seasonally and regionally and persist for days, showing growth and displacement within a region. Topographic clouds tend to appear in or near large, deep craters, and great plains and valleys. Four areas on Mars, Aram, Edom, Libya, and Ophir, form white clouds during most apparitions. Inspection of this area with blue-green (W64), blue (W38A), or vilot (W47) filters will aid in their detection. One topographic cloud that appears in Libya nearly every apparition was reported cloudy from 08 October through 14 October 1990 and again from 16 November though 07 December 1990. White areas are bright surface or near surfase frosts and/or fogs that are seen in all colors. Bright white areas were re ported in Edom (345 W, 4 S) frequently from mid-October through November 1990.