Mars Section Report No. 2

1996 November 1–30

General

During November 1–30, the disk diameter increased from 5”.4 to 6”.5. UK observers Gavin, Gray and Weldrake joined the contributors. OAA data from CMO #181 are included for comparison.

North Polar Region

D. Gray (42-cm refl.) showed an indentation in the cap on November 22 (laxartes/Chasma Boreale). No rifts have been seen in the telescopic observations; the cap is still in the slow regression stage. No return of the NPH has been detected.

Surface features

Gray saw Ganges and Nilokeras well, with hints of Idaeus/Achilles Fons and Lunae Lacus on November 22. Margaritifer Sinus, Meridiani Sinus and Mare Acidalium were all normal and dark, and were captured on Gavin’s red-light CCD images on November 24 (30-cm refl.). The published HST images for September 18 and October 15 showed Propontis I (with its comma-shaped f. end) clearly but the E. and SE (IAU) borders of Elysium, including Trivium Charontis–Cerberus continue to be faint. The Aetheria darkening – or secular enlargement of Morpheos Lacus – remains visible to the NW of Elysium, and that part of Mare Cimmerium visible on the images has the same contour as before, Parker’s November 8 CCD images show the survival of the little dark spot Nodus Alcyonius just S. of Casius–Utopia, the appearance of this region not having altered significantly since 1982.

Dust storms (yellow clouds)

I understand that Parker’s CCD images confirm the September 18 dust storm over the NPC south edge. The narrative of the recently-finished BAA Martian Yellow Cloud Catalogue (1659 to 1993) centains no similar incident. The dense orange colour and lack of brightness of the 1996 event is both striking, and – apparently – unique! I would speculate that the event was associated with the final dispersal of the N. polar hood (see the first report). On 1996 November 22 Gray found two clouds over Ophir and Candor respectively, the former the larger, impinging upon Aurorae Sinus. Both clouds were marginally luminous in yellow (W15) and orange (W22) filters, but rivalled the NPC in brightness in red light (W25). Dust? Gray had the same impression next day in poorer conditions. The Director has contacted the OAA (Minami) and ALPO (Troiani): further observations are awaited.

White clouds

Elysium was not light on the September or October HST images, apart from a few tiny whitish clouds in its NE corner, probably below the resolution limit of ground-based telescopes. The same images showed the orographic clouds over the martian volcanoes at the evening terminator, but no ground-based observations in November received by the Mars Section had adequate resolution to show them. Elysium was not seen bright in the morning or evening in the November observations. Also in November, Gray and Gavin observed strong morning limb haze under CML = 37–44 deg., whilst Chryse–Xanthe and Thymiamata were lighter on the evening side. To the OAA observers, Argyre was light near the CM, but not bright.

Richard McKim, Director

1996 December 3