Mars Section Report No. 7

1997 March 1–15

General

D: 13.2 to 14.1 arcsec. UK weather improved. Jean Dijon joined the BAA team.

North Polar Region

No N. polar haze was evident (Int. light). Hyperboreus Lacus, Rima Borealis and Olympia were still visible.

Surface features

As earlier. The disk has now reached maximum diameter, so please observe intensively over the next few weeks. The Director could glimpse the complex mottled structure of Mare Acidalium in fine seeing; the Mare seemed darkest on the Nf. side. Niliacus Lacus was large and Achillis Pons obvious. Fine details in the nearby deserts were also caught, such as a half-tone shading marking the S. part of classical Gehon. To the north, Iaxartes connected Mare Acidalium to Hyperboreus Lacus.

Dust storms (yellow clouds) and white clouds

Re. the possible dust storm over Tempe alluded to in Circular No. 6, Jim Bell informs me that this was suspected by Dr Leonard Martin on Feb 14 and 15. However, IRTF data on Feb 16 and 17 show no dust. Tempe has not been especially light on the morning side, but Devadas found a bright afternoon cloud over Tempe on Mar 2 (under CM 86 deg.) as well as a small, bright cloud over Alba on the a.m. side. None of the BAA observers reported dust in Tempe in February or March.

White cloud activity is now quite marked. The areas described in the last report remained active, with Chryse and Xanthe both exhibiting a.m. and p.m. cloud. On Mar 3 Knott (22-cm refl., CML 61 deg.) saw a very bright discrete white patch on the a.m. limb over Olympus Mons, visible in blue, but not in red light. The orographic clouds over the Tharsis volcanoes and Olympus Mons continued to show up clearly on the evening side. The Director on Mar 10 and 11 saw Argyre (I) whitish on the morning limb (surface frost?), with white cloud over Tharsis–Ophir–Candor: the latter white cloud extended further onto the disk by running along the S. part of classical Xanthe. Indeed, white cloud upon mid-disk tended to extend east–west along the equatorial border of Sinus Sabaeus (with Edom sometimes separately bright). A number of reports of the ‘equatorial cloud bands’ (ECB) have ben received. Thus with Syrtis Major near the evening terminator, evening cloud over Aeria has been thought by some observers to be thinly connected to morning cloud over Chryse/Xanthe by a bright E–W streak approximately along the martian equator. However, some such observations are simple optical illusions. The Director on Mar 10 and 11 under CML circa 20 deg. did not see ECB connecting the morning and evening bright patches. Objective wispy ECB clouds were imaged by the HST in 1995, and by visual observers for many years previously. Most recently Troiani on Mar 12, CML 65 deg., reported an ECB connecting evening cloud with morning cloud over Memnonia and Tharsis. Southern limb haze was also present. Troiani remarked that a large number of thin white clouds were partly veiling the albedo features. HST images in 1995 showed wisps of white cloud crossing M.Acidalium and thus reducing its intensity. The foreshortened Mare Sirenum may be affected by the haze present along the S. limb at some CML.

Future European missions to Mars

ESA publication D/SCI/96(2), Intermarsnet: Report on the Phase A Study, considers the scientific benefits of a network of martian groundstations. The study is based upon the 2003 launch windows for the ESA M3 opportunity; the idea is to place three groundstations in a triangle of side 1000 km. Proposed sites are: A; Gusev crater [in classical S. Zephyria] at lat. –15 deg., long. 184.5 deg., alt. 0 km; site B: Uranius Patera plains at +29 deg., 93.5 deg., alt. +1 km; site C: Coprates highlands [S. Xanthe] at –2 deg., 49.5 deg., alt. +2 km.

Richard McKim, Director

1997 March 19