Mars Section Report No. 11

1997 May 1–31

General

Between May 1 and May 31, Ls increased from 111 to 126 deg., whilst the apparent diameter shrank from 11.5 to 9.0 arcsec. Mars Pathfinder is still functioning well, and camera tests have been carried out. Larger meteorological and albedo features should remain observable given good seeing. New contributors included John Rogers (UK), Frank Melillo (USA) and Sam Whitby (USA). A Mars Telescopic Workshop (the second of its kind) is planned for October 2–3 in the Tucson mountain foothills, in order to define the state of the martian atmosphere and surface just prior to the Pathfinder landing, and to compare the atmospheric activity in 1997 with recent apparitions. The Director has details for anyone interested in attending.

North Polar Region

The NPC summer remnant appears static; Hyperboreus Lacus was still easy to see at the close of the month. Olympia was still reported by the OAA (Japan) in early May. There was still no real sign of polar haze.

Surface features

Alan Heath’s April drawings showed the Lunae Lacus large and diffuse; the Director had described it as conspicuous in a previous Circular, meaning large rather than dark. Several observers with relatively small apertures have seen the martian volcanoes as albedo features: they are also shown on the newly released Hubble image described above. For instance, Michael Hendrie on May 14 saw Ascraeus Mons as a diffuse dusky smudge (15-cm OG, x330), as did several others. Cave on May 9 saw Nodus Alcyonius tapering to the south.

Dust storms (yellow clouds)

Nothing positive to report.

White clouds

Throughout May, the Tharsis and Nix Olympica orographic clouds remained visible. However, the preceeding limb no longer corresponds with the sunset terminator, and so (since April) the most favourable conditions for viewing the clouds under evening illumination have passed. Elysium appeared lightish near the disk centre and brighter at the limb or terminator. Some observers were lucky enough to see the small Elysium Montes cloud (e.g., Arthur Bowyer (30-cm refl.) on May 1, under CML = 242 deg. Hellas remained bright throughout the martian day. Eridania, Ausonia and Argyre were also light. Libya–Isidis–Aeria and Chryse–Xanthe exhibited diurnal cloud activity, as did Tempe. The Libya–Isidis–Aeria cloud caused Syrtis Major to appear faint in whole or in part at the limb or terminator during May (and April).

More HST images

The HST images described in Report no.10 will feature in the August number of the Journal. Further HST images were acquired on March 20 but not released until May 20. One with CM long. 94 deg. (not reproduced here) shows Acidalium–Hyperboreus, several volcanic calderas, the complex Valles Marineris area and Solis Lacus. The Solis Lacus is still conspicuous, but it is clear that the north-western (e.g., Nf.) part has faded, becoming overlaid with dust. The Phasis area has also faded out. Thus the whole region has returned to something more like its classical appearance, in contrast to the long sequence of changes from 1973 to the present. Greatly foreshortened this year, it has only been well-resolved in the HST images. A blue-light image (same CML) shows Tempe–Arcadia dark, confirming the telescopic impression of a rather strong reddish colour thereabouts. There was no polar haze. The next HST images are due on June 4 , and June 26–29.

Richard McKim, Director

1997 June 2