Mars Section Report No. 5

1997 February 1–15

General

The disk diameter increased from 10.6 to 12.0 arcsec. New contributors were Mrs Sally Beaumont, David Storey and K.M.Sturdy (UK), and ALPO Mars Coordinator Carlos Hernandez (USA). No attempt has been made to analyse all the observations submitted, some of which relate to earlier months (!).

North Polar Region

The North Poalr Cap retains its dark collar but is shrinking appreciably all the time. There are indications thgat it is slightly asymmetric about the rotational pole. Schmude (15-cm refl.) found the cap rather dull under CML 185 deg. on Feb 1, but Warell under CML = 71 deg. on the same night found it bright. Hyperboreus Lacus is now visible near the NPC; Ishadoh (OAA, Jan 31) reported the observation of Olympia.

Surface features

Devadas (36-cm refl.) found Meridiani Sinus well marked, but the prongs of Dawes’ Forked Bay were not well separated, the region between them being shaded. Both Devadas and the Director could see the streak of Deuteronilus well-marked to the north. On Feb 8 the Director found the E. end of Sinus Sabaeus just as it appeared in 1995, with Deltoton Sinus still faded. Nepenthes was invisible. Warell saw Ganges dusky, but paler than Nilokeras. Achillis Pons is a half-tone. Solis Lacus is dark, as are Melas Lacus and Oxia Palus.

Dust storms (yellow clouds)

In an email dated Feb 11, Jim Bell, MarsWatch Coordinator notes that ‘dust activity is remaining rather minimal’ and goes on to write that as the American probes get closer to their encounter dates, NASA ‘will be getting more and more nervous about dust opacity, as this will affect the entry and operations of Pathfinder an the aerobraking manoeuver of Global Surveyor.’

In CMO 184 M.Minami (OAA) queries the source of my statement in Mars Section Circular No. 2 that Parker imaged the September 18 dust storm. I quote from an emailed November ALPO Mars Circular (which had also been sent to the OAA): ‘On Sept. 18, 1996, Don Parker, with help from Carlos Hernandez, imaged a dust storm that was associated with the NPC.’ In the same CMO it is reported that G.Quarra et al. (30-cm Cass.) obtained infrared CCD images showing that NW Elysium apparently contained a small dusty patch on Jan 17. BAA visual data for mid-January do not show this brighter area at lower resolution. Hernandez emailed the Director to report a suspected dust storm in Thaumasia on Jan 29 under CML = 132 deg: Solis L. was seen to be surrounded by a bright region in red, but not in blue light. However, no obscuration was shown on his drawings, and the region was adjacent to very bright S. limb haze. CCD images by Parker on Jan 29 and Quarra on Jan 31 showed no dust activity, whilst BAA visual observations by Devadas, Gray, Storey and Sturdy (Jan 20–26) show only white morning and evening cloud over Thaumasia, so it must be concluded that there was no storm. The brightness of Thaumasia at this season is typical: see the 1980 and 1982 BAA Mars Reports.

White clouds

The morning limb showed more diurnal cloud than the evening terminator. The Director on Feb 8 (22-cm refl., CML = 306–315 deg.) found Libya–Isidis Regio quite bright at the evening terminator, but Hellas to the south was not conspicuously light. On Feb 1 (CML = 71 deg.) Warell (45-cm refl.) saw a broad a.m. limb haze with a local brightening over Olympus Mons. Devadas failed to see Edom as a separate bright area but several times found the general N. border of Sinus Sabaeus rather bright, perhaps affected by light hazes. Edom–Thymiamata was light to McKim on the morning limb on Feb 8. Chryse remained rather bright both at the evening terminator and on the morning limb.

Richard McKim, Director

1997 February 16