BAA Circular 791

2003 July 7

Hellas dust storm alert

Mars has been experiencing a certain amount of dust storm activity recently. The small-scale activity observed up to June 30 will be reported in the August number of the BAA Journal. Since late June, the advancing southern hemisphere spring season has brought more activity as the SPC begins to regress and perihelion approaches.

On July 1 visual and CCD observations revealed a number of small dust clouds around the Hellas basin, with greater activity just N. of the basin in Iapigia. The event was immediately reported as a BAA e-circular. Over the next few days the dust storm expanded to 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. As of July 7, the storm appears to have stopped expanding. Unless another event begins quickly at another longitude, it seems that the dust will slowly settle and the albedo features will regain their usual darkness.

Illustrations of the storm (CCD images by Don Parker) together with some colour drawings by the Director (showing Mars before the Hellas event) were sent to the BBC for their web site at the request of Dr David Whitehouse, and the resulting page (created on July 7) may be viewed at http://news.bbc.co.uk/1/hi/sci/tech/3051548.stm

Another local storm also appeared on or about July 1 over Chryse Planitia. This dust event expanded somewhat to veil parts of Nilokeras and southern Mare Acidalium. A similar event occurred in 1986.

Observers in the UK will be able to watch the western end of the Hellas storm as it appears on the morning terminator, and as many observations as possible should be obtained.

Richard McKim, Director

2003 July 7