This report, including a collage of colour CCD images, was published in the BAA Journal for 2003 October

General

During the past few months the Director has been deluged with observations – mostly in the form of e-mailed CCD images – requiring much time on a daily basis to sort, file and classify.

      Mars was at opposition on August 28, right on martian perihelion (Ls = 250 deg., D = 25.1 arcsec) and was marginally closer to Earth on August 27. The large apparent diameter allowed even those observers with the smaller telescopes to obtain excellent results. Observing from near Paris, Crussaire obtained remarkable images with his 102-mm fluorite OG (Figure 1, below). Even more detail can be seen visually with a large aperture under a high enough magnification, but to draw it accurately is truly difficult! Judging from the bias towards imaging in the observations this year, it seems that many visual observers have been discouraged. But they should continue to send in their work, for their contributions have not diminished in value. Visual observations of martian clouds, sudden changes and delicate colourations continue to be of great value, in addition of course to high resolution drawings.

      During August the writer changed his routine to staying up late rather than rising in the early hours, and continued to enjoy some good views from rural Northamptonshire, despite the slight southward change in Mars’ declination. One of his best views was obtained on August 20 against a slightly hazy sky (Figure 2). More of his detailed drawings will be published later. A deep red filter will help to show the fine details in the dark areas, and will eliminate any nuisance due to atmospheric dispersion. Mobberley was also pleasantly surprised by the state of the seeing at his observatory on the previous night – his best planetary viewing for many years – and made good use of it (inside front cover). Unfortunately the English weather immediately prior to opposition did not cooperate.

      The present account is a continuation of that published in the August issue of the Journal and on this web site. This report covers early to late spring in the martian southern hemisphere, encompassing the period 2003 July 1 (Ls = 213 deg., D (disk diameter) = 16.7 arcsec, tilt = – 21 deg. S) to August 31 (Ls = 251 deg., D = 25.0 arcsec, tilt = – 18 deg. S), considering all work received at the time of writing (August 31).

Surface features

Never before have there been so many fine images of the surface of Mars obtained during one apparition. These reveal the surface in great detail. Recent images show a minor extension of, and a further dark nucleus in, the Aetheria secular darkening on the W. side of the Elysium shield. There have been several surface feature changes as a result of the regional dust storm which began in Hellas in early July (see next section).

Atmospheric activity

Regional dust storm in Hellas

BAA electronic Circular No.109 (July 1) contained the following announcement by the Director: ‘Visual and CCD observations for July 1 reveal considerable albedo changes since the previous day in the areas of Iapigia, Hellas and environs. Several small discrete dust clouds have been observed. Dr D.C.Parker reports as follows in an email dated July 1: ‘Significant changes have occurred over the past 24 hours: 1. Mare Tyrrhenum, Syrtis Minor, and Crocea–Oenotria have lightened considerably, appearing to be covered by a thin whitish cloud… These features were dark and ‘normal’ on June 30… and throughout June. 2. Bright ochre spots [were] rimming Hellas and obscuring Deltoton–Iapygia… Little detail noted on the floor of Hellas.’’

      This activity was due to a rather typical regional dust storm, and its emergence from northern Hellas/Iapigia can be seen from the comparative CCD images by Grafton (Figure 3). A further report appeared in BAA Circular No. 791 (July 10): ‘Over the next few days the dust storm expanded t the east over part of Mare Tyrrhenum and Ausonia and Eridania, with dust veiling Hesperia and part of Mare Cimmerium. Some dust obscured the southern part of Syrtis Major. The SPC has not been affected. Dust also expanded to the west, into Noachis, and some dust cut across the E. end of Sinus Sabaeus. In the last few decades, very similar events have occurred (for example) in 1971, 1986 and 1988… Illustrations of the storm (CCD images by Don Parker)… were sent to the BBC for its web site at the request of Dr David Whitehouse’: http://news.bbc.co.uk/1/hi/sci/tech/3051548.stm

      In the event, after one week, the storm began to subside without spreading beyond the above limits. By mid-July Hellas showed an absence both of bright clouds as well as the subtle floor details that had been visible earlier. (Figure 4) But a new development on the surface could also be seen to have occurred on the western border of the disturbance: Mare Serpentis was greatly broadened, and the E. end of Deucalionis Regio was seen to have darkened, due to dust removal from the surface. (Figure 4 and colour CCD images) There were other changes, too. The aspect of the southeast part of Mare Tyrrhenum was altered somewhat, being invaded in several places by bright matter from the Ausonia side due to dust newly settled on the martian surface. Such developments – witnessed in considerably more detail this apparition than in the past – are typical results of there having been storms in these longitudes.

Other smaller scale dust storm activity

At least four dust storm events of brief duration and extent have appeared over portions of Valles Marineris (see the image by Ikemura, in colour CCD images) and in Chryse (see the image by Grafton, ditto). The latter events were located within the Chryse Planitia basin. The first began on July 1, dust expanding to veil parts of Nilokeras and streaking across southern Mare Acidalium. The second began in late July. All were typical storms, reminiscent of several past events. Full details will feature in the final Section Report. Together with the Hellas event these storms caused a small amount of suspended dust to be distributed over large regions of the planet. Although not detectable directly, the suspended dust could be seen to tinge the morning limb (over a wide range of longitude) a distinct yellow colour until mid-August. Furthermore, white cloud activity was very low throughout July.

Will there be a great dust storm in 2003?
 

Although crystal ball gazing will be frowned upon in some quarters, the Director will briefly indulge, even though (as will be seen) our ability to make dust storm predictions based upon past records is not much better than guessing future London weather by observing a piece of seaweed nailed to the door of Burlington House. It is often written that in perihelic oppositions, any great storm is preceded by a regional event. This is generally true, at least in those oppositions when the great storm does not occur close to the start of southern spring. The converse, however, does not necessarily follow. Some perihelic oppositions proceed with a string of local and regional events only. Thus in 1988 there were significantly large regional storms at Ls = 212 deg. (starting in Hellas) and Ls = 313 deg. (Thaumasia) but no great storm.

      Selecting only those oppositions displaying a planet-encircling storm well observed from Earth we have 1909, 1924, 1956, 1971, 1973, 1975 and 2001. The events of 1909 and 2001 began unusually early just after the start of southern spring. The start of the encircling storm in 1975 was fairly well documented, but the period immediately beforehand was hard to observe due to the tiny disk diameter. We are left with three adequately observed years – 1924, 1971 and 1973, in which there were significantly large regional events observed in advance of encircling storms:

Terrestrial date of start       Ls          Terrestrial date of start                 Ls        Interval(s)      
of regional storm                              of planet-encircling storm                        in Ls

1924 June 11 (Hellas)        200
1924 October 8 (Hellas)     274        1924 December 9 (Hellas)           311      74, 37
1971 July 10 (Hellas)         213        1971 September 22 (Hellas)        260      47
1973 July 16 (Hellas)         244        1973 October 13 (Thaumasia)     300      56

Thus the interval in Ls between the last significant regional event in the S. hemisphere and the start of the encircling storm is 47+10 degrees in Ls. The writer’s experience is that a significant amount of time is needed between the larger events for dust to settle, and for the atmospheric opacity to drop to a level at which dust-raising may again proceed.

      The 2003 July Hellas regional storm described began at Ls = 213 deg. Extrapolating from the 1924–73 data suggests a plausible terrestrial date range of August 28 (Ls = 250 deg.) to September 27 (Ls = 269 deg.) during which a planet-encircling event might begin. This range is of course a very reasonable one to predict, because Ls = 250 deg. corresponds to perihelion and the later limit corresponds with the summer solstice for the S. hemisphere, which will be reached on September 29 (Ls = 270 deg.). This is not, however, a serious prediction. We must remember that our sample available for forecasting is not very large, and that in any case history teaches us that the chance of a planet-encircling storm following a large regional event is only about 32%, or about one in three (see R.J.McKim, Telescopic Martian Dust Storms, Mem. Brit. Astron. Assoc., 44 (1999)). All we can really say is that if there is to be a great storm, it will begin before Ls = 360 deg.

White clouds

Throughout July there was little sign of crystal clouds in the martian atmosphere, the Hellas dust having warmed the planet’s atmosphere. But as dust fallout continued into August, coupled with the release of volatiles from the SPC, white cloud activity began to appear. The NPH also returned to prominence.

      White evening clouds appeared over the Tharsis volcanoes and Olympus Mons. Most prominent was the little cloud near Phoenicus Lacus (Figure 5). Morning clouds of a bluish tint were recorded over the rising Syrtis Major in August, and both morning and evening clouds were noticed over Aeria.

The polar regions

By August, the retreat of the SPC had noticeably quickened, and changes in the contour of the cap could be seen in observations a few days apart. The dark surroundings of the cap persisted through July and August. As the cap retreated its well-known axial asymmetry developed, and the bright patches formerly within the cap became projections or outliers. Thus Novus Mons became separated from the cap in accord with the usual seasonal cycle, and Argenteus and Thyles Mons (Figure 5) appeared as outstandingly bright areas near the cap periphery. (See the images, inside front cover.) High resolution observations revealed smaller, unnamed, bright spots, fine rifts and darker patches within the SPC, and such observations are certainly the most detailed every obtained from Earth. There will be plenty of material to discuss the cap recession when a detailed analysis is made later.

      The north polar hood was quite prominent again in August. As in past years it was highly asymmetric about the rotational pole and tended to be displaced to a higher latitude in the longitude of Mare Acidalium (a region of high thermal inertia).
 

Grazing occultation of Mars
 

This event (July 17) was not observable from the UK. Reports came from Parker and Beish (Figure 6 and colour CCD images), and from Phillips, all observing from the USA. The dark limb partly cut across the martian disk.

The martian satellites
 

Phobos and Deimos were both imaged on August 23 by Akutsu with a 32-cm Newtonian, and Biver reported seeing them on several occasions with a 400-mm aperture.

Figure 1 : CCD image by Daniel Crussaire, 102-mm OG, Philips Vesta Pro, Champigny-sur-Marne, France, August 19d 01h 51m, CML = 76 deg. (Originally submitted as a colour composite.) Remarkably fine details of the regions of Solis Lacus, Valles Marineris, etc. The smallest details are not perfectly resolved by this aperture and are recorded as slightly enlarged oases, etc.
    

 
Figure 2 : Drawing by Richard McKim with 410-mm Dall–Kirkham Cass., x410 with W25 red filter, August 20d 23h 25m, CML = 23 deg. Hellas light on the evening terminator; Argyre dull near the CM. Intricate fine detail seen, the observer remarking upon the coarse mottling of the dark areas of Margaritifer Sinus, Mare Erythraeum and environs. Notice the small dark ‘oases’ in southern Chryse–Xanthe.

Figure 3 : Red-light CCD images by Ed Grafton, 355-mm Schmidt–Cass., ST5, Texas, USA. Left: 2003 June 28d 09h 25m, CML = 302 deg. Right: 2003 July 2d 09h 43m, CML = 268 deg. On the right-hand figure the initial dust clouds of the Hellas regional storm can be seen around the great basin, especially at the northern periphery over Iapigia.
    

 
Figure 4 : Red-light CCD image by Damian Peach, 203-mm refl., Philips ToUcam, July 28d 02h 23m, CML = 281 deg. Fine details around Syrtis Major. The Mare Serpentis region is much broader and darker than it was before the regional Hellas dust storm. Hellas shows less floor detail than it did before the storm.

   
Figure 5 : CCD image by Clay Sherrod, 410-mm Schmidt–Cass., Philips ToUcam, Arkansas, USA, August 19d 07h 37m, CML = 160 deg. (Originally submitted as a colour composite.) Note the bright orographic evening cloud near Phoenicus Lacus and another fainter one to the north over Olympus Mons (Nix Olympica).
    

 
    
Figure 6 : Sketch by Jeff Beish, 152-mm refl., x185, Florida, USA, July 17d 08h 32m, showing the grazing occultation of Mars by the Moon.

The next report

Our next report (scheduled for the December Journal) will deal with the post-opposition observations of September and October. Any material for consideration must reach the Director by the last week of October. The arrival of ESA’s Mars Express (carrying Beagle 2) at Mars in late December/early 2004 January is awaited with much interest. This mission is expected to map the distribution of water and to measure the thickness of the polar deposits as well as studying the martian ionosphere.
 

Richard McKim, Director