Beagle 2 needs no introduction to UK observers. Everyone will know of the work of the Open University’s Professor Colin Pillinger, the driving force behind this British initiative. Beagle 2 will search for evidence of martian life when it lands in Isidis Regio in late 2003. A regular newsletter is edited by Professor Pillinger and his wife Judith. The following article was written by the Mars Section Director at the request of Professor Pillinger, and an an abstract of it was published in the Beagle 2 newsletter.
Dust storm activity at the Beagle 2 landing site: the telescopic story
Telescopic observers refer to Beagle 2’s landing site as Isidis Regio, which is the name given to this region by Giovanni Schiaparelli in the nineteenth century. It is an impact basin some 2 km deep, with a sharply rising escarpment on the S. and W. sides, bordered by the classical albedo markings Mare Tyrrhenum and Syrtis Major, respectively.
The telescopic records for the last three centuries up to and including 1993 were exhaustively searched by myself in my BAA Memoir on telescopic dust storms. For convenience of analysis I grouped Isidis Regio together with the nearby Libya, Hesperia and N. Ausonia. These dust storm ‘emergence sites’, dominated by the activity in Libya and Isidis Regio, exhibited telescopic activity during the period 1877–1959. Indeed, in 1964 the Lowell Observatory veteran Earl C. Slipher described Libya (and therefore this group of sites) as having been the most active of all the dust storm sites on the planet. But since 1959 the area and its surroundings have become more of a dust sink than a dust source, the dust settling over the once formidable dark albedo feature called Nepenthes, and totally obscuring it by the 1980s. In the past, activity over Libya or Isidis had often led to a marked darkening of this feature.
2001 marked a possible turning point in martian climate patterns. The 1970s was an unusually dusty epoch, and Mariner 9 and the Vikings witnessed an atypically dusty Mars. Since 1983 there had been no great planet-encircling storm: that is, until 2001 June 26. The latter event started at Ls = 185 degrees, seasonally the earliest ever by a narrow margin. (Ls, the areocentric longitude, is a seasonal indicator for the martian year. The seasons occupy 90 degrees each, and N. spring starts at Ls = 0. Thus at Ls = 185, S. spring had just begun.) The 2001 event also had approximately the same duration as the greatest ever historical storm: the truly global event of 1971. And of relevance to us here, although the 2001 activity began over the traditional emergence site of N. Hellas, there were early discrete dust clouds over both Hesperia and Libya. A full preliminary description appeared in the BAA Journal for 2002 June (J. Brit. Astron. Assoc., 113, 119–121 (2002)).
Historically, Isidis Regio ‘events’ have been limited to local or regional status. The site is clearly under strong solar control for the larger events clump into two groups in Ls, corresponding to periods of high insolation with the Sun nearly overhead. Seasonally the site has produced events from Ls = 171 through 360, up till 34 degrees. The events there have been described in great detail in the BAA Memoir. The local events showed little movement, but the more major regional events rapidly grew in size, the storm front progressing mostly S. and SE, obscuring the albedo markings Mare Tyrrhenum, Hesperia and Mare Cimmerium. The largest of these events have thrown dust into suspension around at least half the circumference of the planet.
Unless the 2001 encircling storm represented a real turning point in martian climatic terms, Isidis Regio is unlikely to produce any telescopic storms during Beagle 2’s mission in 2003. But the smallest dust devils are not visible form Earth, and so do not constitute part of the historical statistics, and it is such phenomena that could be a source of trouble. Like all forecasters we must wait and see, and, above all, keep our fingers crossed!